Energy - edisciplinas.usp.br · intensities; material, energy, CO2, capital and land area. Includes Coal and Gas pow- ... 12,000–18,000 . 800–1130 : 35–50 . Tidal, barrage :

Mike Ashby(1), Julia Attwood(1), and Fred Lord(2)1. Engineering Department, Uni-versity of Cambridge, UK2. Department of Materials Sci-ence and Metallurgy, University of Cambridge, UK2nd edition, January 2012, © 2012 Granta Design

A description of the Low Carbon Power edition of CES EduPack. Discusses different low carbon power systems and their resource intensities; material, energy, CO2, capital and land area. Includes Coal and Gas pow-er for comparison. Keywords: Renewable ener-gy, Low carbon power, Re-source intensities, Materials, Area, Capital, Energy, CO2, Lifetime, Current installed supply.

M. F. Ashby a,b and Michael Smidman a a. Engineering Department, Uni-versity of Cambridge, UKb. Granta Design, Cambridge, UK Version 1.1, January 2010, © 2010 Granta Design

A background on Nuclear Power Systems. Describes the different reactor types, their associated materials and the nuclear properties in the Elements database. Keywords: Nuclear, Fission, Fusion, Reactors, Materials, Selection, Design.

Discusses the need for Energy Storage Systems and the process of selection. Describes different types of Energy Storage Systems and their resource intensities. Keywords: Energy storage systems, Resource inten-sities, Materials, Energy, Capital, Material, CO2, Con-struction.

Mike F Ashby and James Poly-blankEngineering Department, Universi-ty of Cambridge, UK Version 2.0, January 2012, © 2012 Granta Design

Materials for Low Carbon Power

Materials for Nuclear Power Systems

Materials for Energy Storage Systems

White Paper Series

Energy

ECO DESIGN

Low carbon power © Granta Design, February 2011

A White Paper

Materials for Low-Carbon Power

Mike Ashby and Julia Attwood

Engineering Department and Granta Design, Cambridge, UK First published January 2011, This Version (1.1) February 2011

© 2011 Granta Design Ltd

Table of Contents 1. Introduction and synopsis ........................................................................................................................... 1

2. The resource intensity of power sources–the big picture ........................................................................... 2

3. Conventional fossil-fuel power: gas and coal ............................................................................................. 8

4. Nuclear power .......................................................................................................................................... 10

5. Solar energy: thermal, thermo-electric, and photo-voltaics ...................................................................... 11

6. Wind power ............................................................................................................................................... 13

7. Hydro power ............................................................................................................................................. 15

8. Wave Power ............................................................................................................................................. 16

9. Tidal Power ............................................................................................................................................... 17

10. Geothermal power .................................................................................................................................... 18

11. Biomass .................................................................................................................................................... 19

12. Summary and conclusions ....................................................................................................................... 20

13. Appendix: Approximate material intensities for power systems ............................................................... 21

14. Appendix: Definitions ................................................................................................................................ 25

15. Appendix: Further reading ........................................................................................................................ 27

Low carbon power © Granta Design, January 2011 1

Table 1: Alternatives for power generation with current (2008) installed capacity and growth.

1. Introduction and synopsis If you want to make and use materials the first prerequisite is energy. The global consumption of primary energy today is approaching 500 exajoules (EJ)1

• to adjust to diminishing reserves of oil and gas

, derived principally from the burning of gas, oil and coal. This reliance on fossil fuels will have to diminish in coming years to meet three emerging pressures:

• to reduce the flow of carbon dioxide and other greenhouse gases into the atmosphere

• to reduce dependence on foreign imports of energy and the tensions these create

The world-wide energy demand is expected to treble by 2050. The bulk of this energy will be electrical. How will it be generated when oil and gas reserves become depleted? And how much time will the transition take? The options are listed in Table 1.

1 1 MJ = 0.28 kW.hr = 948 Btu. 1 quadrillion (1015) Btu is called a “Quad”, symbol Q. Thus 1 EJ ≈ 1 Q.

We have history as a guide for transition times. Figure 1 shows the way in which the energy sources for delivered power have change in the last 150 years (IEA, 2010). Past transitions have taken about 40 years for 50% replacement. Speed, of course, depends on urgency and ability to manage change, and both, in the coming years, may be greater than in the past. But the message of the figure is clear: a major shift in a major underpinning technology such as power generation takes decades.

Renewable power systems draw their energy from natural sources: the sun (through solar, wind, and wave), the moon (through tidal power), and the Earth’s interior (through geothermal heat). But it is a mistake to think that they are in any sense “free”. They incur a capital cost, which can be large. They require land. Materials and energy are consumed to construct and maintain them, and both construction and maintenance have an associated carbon footprint.

Power system Current installed capacity

Growth rate Delivered cost

(GW) (% per year) ($/kW.hr)

Conventional (coal) 2800 1.5 0.003–0.009

Nuclear–fission 400 2.2 0.01–0.02

Nuclear–fusion 0 0 Unknown

Wind 204 20-40 0.003–0.010

Solar PV 154 40 0.025–0.03

Hydro 675 4.5 0.003–0.014

Wave 0.004 50 0.02–0.07

Tidal 0.26 10 0.009–0.15

Geothermal 8.9 20 0.003–0.01

Biomass 35 16 0.007–0.02


Figure 1: The replacement of one source of power by another over the last 150 years (data from IEA, 2010).

How can these alternative power systems be compared? We do so by examining their resource intensities2

The main findings are introduced in Section

. By this we mean the quantity of capital, land area, energy and carbon-release per kW.hr generated. This allows a calculation of the “pay-back” time energy: the number of years of plant operation before the energy delivered first exceeds those committed to build and operate the plant. Equally importantly, each system has a material intensity, meaning the quantities in kg of materials required to construct it. If a chosen power system were adopted globally on a scale that could deliver significant amounts of power it would create a demand for materials that could distort the materials supply chain. We explore this by comparing the possible material demand with current production, highlighting potential supply shortages.

2. Subsequent sections develop the background and examine the implications. The data form part of the CES EduPack database for Low Carbon Power, which can be used to construct many of the figures shown in this paper.

A warning before we start. The resource intensities of a given power generating system depend on many things–on the type and scale of the system, on its location and on the way it is managed. The intensities are tabulated and plotted as representative ranges, but there is no guarantee that they enclose all members of a given system.

2 Similar metrics are used by IAEA (1994) and San Martin (1989), reviewed by Rashad and Hammad (2000).

2. The resource intensity of power sources–the big picture

The current world electric power-generating capacity is 2,200 GW. At present about 66% of this derives from fossil fuels, about 16% from hydro-power, 15% from nuclear, and 3% from other renewable sources (IEA, 2010). Electric power appears to be the future for almost everything except air and space transport. Before examining individual systems for generating it, we should look at the electric energy-mix to which individual nations have committed themselves. The fossil / nuclear / renewable triangle of Figure 2 shows that this is diverse. The green arrows indicate the way changes of the mix reduce carbon emission or reduce dependence on fuels, fossil or nuclear. The smaller triangle and the caption explain how to read the diagram.

In one way this is a reassuring picture. We are not all stuck in one corner. Nations particularly endowed with natural energy sources (Norway, Brazil, Canada, Iceland) have developed cost-efficient ways of using them. The high commitment to nuclear power in France demonstrates that it is a viable option. Most of the nations in the bottom-left corner have renewable or nuclear options, but few have large untapped hydro or geothermal resources, and even fewer have the confidence in nuclear technology on which France has built its energy-generating base.


Figure 2: A map of the distribution of electric power generation from fossil fuel, nuclear and renewable sources. The map is read in the way shown in the smaller triangle:

a vector at 3 o’clock for nuclear, one at 7:30 for renewables, and one at 10:30 for fossil.

Power system Capital intensity

Area intensity

Material intensity

Construction energy

intensity

Construction carbon

intensity

Capacity factor

(k$/kWnom) (m2/kWnom) (kg/kWnom) (MJ/kWnom) (kg/kWnom) (%) Conventional, gas 1–1.5 1-4 605–1080 1730–2710 111–211 75–85

Conventional, coal 2.5–4.5 1-4 520–1800 3580–9570 308–628 75–85

Nuclear, fission 3.5–6.4 1-3 170–625 2000–4300 105–330 45–55

Solar PV, single crystal

20.5–44.3 45–100 73–120 25,700–43,700 1,400–2200 8–12

Solar PV, poly-silicon 12.5–20.5 50-200 120 -220 23,700–33,700 630–1400 8–12

Wind, land-based 1.1–2.4 200–350 200–600 4380–9014 156–692 25–28

Wind, off-shore 5.5–8.0 200–330 1016–2000 12,000–20,000 840–1232 35–45

Hydro, earth dam 4.5–6.0 91–200 900–2000 7260–15,000 630–1100 45–65

Hydro, steel reinforced dam

5.5–7 80–150 1000–5700 30,000–66,000 2000–7000 50–70

Wave 1.2–4.4 42–100 1000–2000 22,950–31,540 1670–2070 25–40

Tidal, current 10–15 150–200 350–500 12,000–18,000 800–1130 35–50

Tidal, barrage 1.6–2.5 200–300 5,000–50,000 30,000–45,000 2400–3520 20–30

Geothermal, shallow 1.15–2 1–3 61–500 2400–3500 160–250 75–95

Geothermal, deep 2–3.9 1–3 500–1200 25,000 -65,700 1700–3900 75–95

Biomass 2.3–3.6 5,000–10,000 69–500 4,000–15,800 400–1800 50

Table 2: Average approximate global resource intensities for power generating systems.


Table 2 summarizes the resource intensities and typical capacity factors of alternative power systems. The data from which they are derived appear in subsequent sections of this paper. We define resource intensity as the quantity of each resource per kW of nominal, power generating capacity, nominal meaning the power rating of the system. The actual power generated by the system is less than the nominal rating because the capacity factor–the fraction of time that the system operates at full power–is low. Thus for nuclear power the capacity factor is typically 50%. That for hydro power is about 55%, for off-shore wind about 35%, for land-based wind about 25% and for photo-voltaic solar power, about 10%. These factors are not included in calculating the intensities in Table 2 because they vary with location, but they are included in later estimates of the actual energy produced.

Some of the data in Table 2 are easy to find but others are not. Some have to be estimated from diagrams or schematics of the system, some deduced by analogy with other systems with similar structural requirements, and some inferred from the physics on which the system depends. The material intensities vary greatly with the design and location of the system–alternatives choices exist for magnetic materials for generators, for the semiconductor panels for solar cells, and for other specialized sub-systems,

allowing wide variation. That means that the precision is low. But the differences between the resource intensities of competing systems is sufficiently great that it is still possible to draw meaningful conclusions.

The remainder of this section examines what can be learnt from the data in Table 2.

The capital intensity is least for biomass, land-based wind, favorably-located geothermal sources, and conventional fossil-fuel burning stations–all others at present cost more per unit of nominal generating capacity. More striking are the great differences in area-intensity. The energy densities of wind and solar power are low. Capturing this energy requires systems that cover a much larger area than conventional or nuclear power. With this goes large differences in material intensity, construction energy and the carbon emissions associated with construction. Because of this, deploying renewable power systems on a scale that would provide even half of the expected energy demand of 2050 will require very large quantities of materials. We explore the materials consequences in more depth in subsequent sections.

Figure 3: The area and material intensities of power systems, based on actual power output during life.


Figure 4: The capital and energy intensities of construction of power systems, based on actual power output during life. The low capacity factor of solar PV systems in temperate climates makes them expensive in both

capital and energy.

The data of Table 2 are displayed in the next four figures. The first (Figure 3, on page 4) shows the material and area intensities. For a meaningful comparison the nominal power will not do; instead we need the intensities associated with the actual power output averaged over a year. To calculate these we divide each nominal intensity in Table 2 by the capacity factor expressed as a fraction to give “actual” material and area intensities. The most striking thing about the figure is enormous differences between the area intensities of different systems. Gas and coal-fired power stations, nuclear and geothermal have small footprints of around 3 m2/kWactual. All others require an area 50 to 500 times greater. For offshore wind and wave power this may not be a problem, but for land-based systems the loss of land that could be used for other purposes may present difficulties. Conventional, nuclear and geothermal systems also have lower material intensities than many of the others, but to understand the material implications of alternative power systems we must examine their bills of materials in more depth. This we do in subsequent sections of this paper.

The capital and energy intensities for the construction of the power systems, plotted in

Figure 4 (above), are calculated by dividing the nominal intensities by the capacity factor, as with material and area. The two actual intensities are approximately proportional. This arises partly because systems that are energy-intensive to construct are (inevitably) more expensive than those that are not, and partly because the actual power delivered by those with low capacity factors (like solar photo-voltaics) is much less than the nominal rating of the system, inflating both intensities.

Figure 5 (below) shows the balance between the energy to construct the power system and the energy it generates per year in MJ of electrical energy, per nominal kW of generating power (31,400 x capacity factor MJelec/kWnom). The alternative scales show the energy in kW.hr instead of MJ (1 kW.hr = 3.6 MJ). It should be remembered that the construction energy is expressed in oil equivalent, whereas the delivered energy is electrical. Contours show the energy pay-back time, equal to the time in years before the delivered energy exceeds that invested in construction of the plant. The data suggest an energy pay-back time of 1–2 years for wind and hydro, rising to 3–6 years for solar and tidal barrier.


Figure 5: Energy pay-back: the balance between construction and delivered energy.

Figure 6: Approximate release of carbon to the atmosphere from the building and operation of alternative power systems, assuming a 20 year life.

None are carbon free, but all emit less than coal.


Figure 7: Current (2008) annual world production of twenty nine strategic elements. Many of them are used in power generation.

A major shift from one power system to another can put pressure on their supply.

Figure 6 (page 6) brings out the large differences in carbon emissions of power systems, measured in kg of CO2 per kW.hr of delivered energy, based on a system life of 20 years. Each bar describes the sum of three terms:

• construction carbon intensity (kg/kWnom) pro-rated by the energy delivered over the system life in kW.hr/kWnom, taking the life to be 20 years3

• carbon release associated with plant operation, estimated at 0.03 kg/kW.hr for coal and 0.02 kg/kW.hr for the others (White and Kulcinski, 2000)

• carbon release from fuel (where used), per kW.hr of delivered electrical power4

The figure demonstrates that no power system is completely carbon free because of the contributions from construction and maintenance, but renewable systems produce 5 to 30 times less carbon than a fossil-fuel station.

In subsequent sections we examine power systems in turn, focusing on the underlying physics of their operation and the implications for material supply if they are deployed on a large scale. One concern that emerges is the demands 3 Equal to (construction carbon intensity / 1.75 x 105 C) where C is the capacity factor. 4 For coal this is equal to 0.088 kg/MJ x 3.6 MJ/kW.hre / 0.33 (conversion efficiency from coal to electric power) = 0.96 kg/kW.hr. For gas it is equal to 0.055 kg/MJ x 3.6 MJ/kW.hre / 0.38 (conversion efficiency of gas to electric power). For nuclear fuel it is approximately 0.022 kg/kW.hre.

made on materials deemed to be strategic, either because the global supply is limited or because the main ore-bodies are localized in such a way that a free market does not operate. Figure 7 (above) provides background for discussing this. It shows the 2008 world production of 29 elements that are considered to be strategic. Later sections compare the demand of each power system for these elements with the world production, highlighting where material constraints are likely. To do this we examine a hypothetical scenario: that 2,000 GW, roughly equal to the current world generating capacity or one third of that projected for 2050, were to be replaced by a given alternative power system over a period of 10 years. From this we calculate the fraction of current world production of each strategic material that would be required to make the replacement, revealing where material supply might be a problem.

The CES EduPack database for Low Carbon Power The latest CES EduPack system includes a database of low-carbon power systems and the materials of which they are made. It is a specially adapted version of the CES EduPack Level 3 database, expanded to have a new data-table, that for “Low-carbon energy systems”. The additional data-table, with which the software opens, contains records for the power systems described in this Paper. Each starts with a description and schematic followed by selectable fields containing the data of Tables 1 and 2. Each power system record is linked to records for the principle materials of which it is made, which in turn are linked to the processes that can shape, join and finish them.


The Low Carbon Power database allows students to:

• explore the individual systems

• create resource-intensity charts (like those of Figures 3 through 6), and world production plots (of which Figure 7 is an example)

• adjust these by the capacity factors to show real demand and how much capacity factor matters

• plot actual resource demand for a given required power from any one of the systems (by multiplying intensity by proposed demand to find the absolute requirement)

• access, with one mouse-click, datasheets for the materials involved in the construction of each system, with general, mechanical, thermal, electrical, and eco-properties

• from these material datasheets, access datasheets for the processes that can shape, join and finish them

The CES EduPack database for Low Carbon Power is designed to support teaching and stimulate independent thinking by giving students fast access to relevant information and the ability to move further via the links to much more.

3. Conventional fossil-fuel power: gas and coal

The use of fossil fuels as a source of energy started in the 1700s and has grow in scale ever since. The high energy-density of fossil fuels makes them easy to transport and allows a large amount of power to be generated in a compact plant taking up little land area. Today, they are our principal source of power but they are also a source of political and social tensions as the limits to their supply become more apparent. And there is concern about the emissions that attend their use. Fossil fuel power generation is the bench-mark against which alternatives must be judged.

Natural gas It is said that natural gas, leaking from the ground and burning, so awed the people of Delphi that the place became both a shrine and an appropriately mysterious seat for an oracle. Be that as it may, natural gas is the superstar among fossil fuels. It is the cleanest-burning, the easiest to transmit, and in transport the least polluting. Natural gas is primarily methane, with small amounts of ethane, propane, butane, hydrogen sulfide, and other impurities that are removed in the refining process. Gas was at one time made from coal but today is drawn from gas/oil reservoirs, where it is found along with heavier

hydrocarbons. Many gas reserves are now depleted. While others remain to be exploited, most are deep and lie beneath water or ice.

For electricity generation, gas is either burnt in a furnace to produce steam, or combusted in a gas turbine. In combined cycle units, a gas turbine produces electricity and the waste heat generates steam to drive a secondary steam turbine, giving conversion efficiencies above 50%. Gas can be used as a fuel for reciprocating engines, and on a small scale, either commercially or residentially, natural gas fuel-cells allow small-scale electricity generation. In addition to its use as a fuel, natural gas is also crucial for the manufacture of plastics, fabrics and other chemicals and materials. It is, however, a finite resource, the production of which is expected to peak and then decline before 2050. The number of high-tech industries that rely on natural gas highlights the importance of conserving it for the future. This conservation imperative and the emissions associated with burning gas for energy motivate the efforts to find alternative sources of power, described below.

Coal Coal is the sun’s energy in fossil form. There are four basic types, classed by their carbon content and calorific (heat) value. In order of decreasing carbon content, they are anthracite, bituminous, sub-bituminous and lignite. Anthracite is the hardest of the four, with 86–98% carbon and a calorific value of 6.5–7.5 MJ/kg. It is the cleanest-burning, making it attractive for heating and electricity generation. Bituminous coal, the most common type, contains 46–86% carbon and has a calorific value of 5.3–7.2 MJ/kg. It is used for power generation and to make blast-furnace coke for iron-making. The final two classes are soft and burn with much smoke and flame. Both have a carbon content of 46–60% but sub-bituminous coal gives a higher energy return with a calorific value of 4.0–6.2 MJ/kg compared to 2.4–4.0 MJ/kg for lignite. All forms of coal are used to generate electricity in large plants, but they also have important secondary uses: many plastics and organic chemicals rely on the distillation of coal for feedstock.

The global reserves of coal far exceed those of oil or gas. If we are to generate power from fossil fuels then we will be driven to build coal-fired stations. Coal contains hydrogen, nitrogen, sulfur and many other elements besides carbon. Combustion releases not only green-house gases such as carbon dioxide but also the oxides of sulfur and nitrogen that cause acid rain. These environmental concerns have prompted the development of clean-up technologies. Washing reduces the nitrogen content of coal. Scrubbing, spraying a lime-water mix into the smoke, removes acidic oxides of sulfur by neutralizing them. Carbon capture and storage (CCS), an


Figure 8 Coal fired power station (Based on an original by BillC, Wikipedia)

Figure 8: Coal fired power station (based on an original by BILLC, Wikipedia).

Figure 9: Resource demands for strategic materials used in conventional power systems.

emerging technology, captures the carbon dioxide, compresses it and stores it in spent oil and gas reservoirs. This possibility allows coal-derived power to be included in the list of low-carbon power sources, although the immaterial implications of CCS are not yet known.

Electricity is generated in coal fired power stations by using the heat of combustion to turn water into steam. The steam then drives turbines to generate electricity that is fed to the grid. The typical thermal efficiency of coal power generation is 37%. Figure 8 shows the layout and identifies the material used in the largest quantities. An approximate bill of materials for a coal fired power station appears in the Appendix. It is expressed as material intensities per rated kW of generating capacity, kg/kWnom. As already explained, the actual output of any power source, averaged over life, is less than the nominal or rated value because the capacity factor–the fraction of time

that the system operates at full power–is less than one. Thus the actual material intensities, kg/kWactual, are larger than the nominal ones.

If a sufficient number of new coal fired power stations were built over the next 10 years to provide 2,000 GW of additional capacity, would the drain on material supply be significant? As an indicator we divide the annual material demand that this implies by the current annual global production of that material, expressing the resulting demand ratio in %. Thus a demand ratio of 1% means the construction would require a mere 1% of global production; a demand ratio of 100% means the entire global production would be consumed. The results, for strategic materials, are plotted in Figure 9. Only chromium gives cause for concern.


Figure 10: The pressurized water reactor.

Figure 11: Demand ratios for strategic materials used in nuclear power systems.

4. Nuclear power Nuclear power is seen by some as a viable means of generating the electrical power needed to meet future needs. Others perceive it to be only an interim solution and one with incipient risk of accident and nuclear proliferation. Today, many governments take the view that, despite the risks, nuclear power offers the fastest, cheapest way to reduce dependence on imported hydrocarbons, cut carbon emissions and assure energy supply to 2050.

Nuclear power derives from the energy release on the fission of a nuclear fuel–typically uranium-235–when it captures neutrons. The briefly formed uranium-236 is unstable and breaks into lighter nuclei, releasing more neutrons to give a chain reaction. The energetic neutrons are slowed by a moderator, usually water, converting their kinetic energy to heat. Fuel consumption is roughly 1 mg of uranium per kW.hr of electrical energy. Fuel is

replaced every one or two years, during which time the plant is shut down.

Currently there are 436 nuclear power stations world wide, of which 60% are pressurized water reactors (PWRs) and 21% are boiling water reactors (BWRs). The remaining 19% include older CANDU and gas-cooled reactors and new, more advanced 4th generation reactors. The most controversial issue surrounding the large scale use of nuclear power is that of dealing with radioactive waste, which requires secure storage for up to 1000 years.

The core of a pressurized water reactor (Figure 10) has some 200 tube assemblies containing ceramic pellets of enriched uranium dioxide (UO2) or of a mixture of both uranium and plutonium oxides known as MOX (mixed oxide fuel). These are encased in a cladding of a zirconium alloy, Zircaloy 4. Either B4C-Al2O3 pellets or borosilicate glass rods are used as


burnable poisons to limit the neutron flux when the fuel is new. Water, pumped through the core at a pressure sufficient to prevent boiling, acts as both a coolant and a moderator, slowing down high energy neutrons. The power is controlled by control rods inserted from the top of the core and by dissolving boric acid into the reactor water. The boron carbide (B4C) or Ag-In-Cd alloy control rods are clad in Inconel 627 or Type 304 stainless steel tubes. The primary pressurized water loop carries heat from the reactor core to a steam generator under a pressure of about 15 MPa, which is sufficient to allow the water in it to be heated to near 600 K without boiling. The heat is transferred to a secondary loop generating steam at 560 K and about 7 MPa that drives the turbine. An approximate bill of materials appears in the Appendix. Installing 2,000 GW of additional nuclear capacity over the next 10 years carries the implications for strategic materials plotted in Figure 11.

5. Solar energy: thermal, thermo-electric, and photo-voltaics

If you think of the earth as a flat disc facing the sun, then the energy the sun beams onto the disc is a prodigious 1 kW/m2. Multiplying this by the disc area (roughly 1014 m2) gives 100,000 TW (1017 W), more than a million times more than we at present use. Not all this energy is accessible: some is reflected, some absorbed in the atmosphere, and much falls where it can’t be reached. Nor is it evenly distributed: the length of day and the angle that the surface presents to the sun differ between the poles and the tropics. Even so, the sun’s energy per unit area in a temperate country averages 100 W/m2; that in the tropics can be three times larger.

Thermal systems If a black panel is placed so that photons fall onto it, their energy is absorbed as phonons–lattice vibrations–raising its temperature. The energy can be harvested by passing water or air through the panel, providing low-grade heat for water or space heating. Focused systems concentrate the radiation sufficiently to create steam to drive turbo-generators. Some of the incoming energy is lost by reflection, and some is lost by parasitic conduction or convection giving overall conversion efficiencies of 30–50%. If this heat is then used to generate electricity there is a further conversion loss, reducing the efficiency to 8–15%.

The main materials issues here are those of durability and cost. The materials of the panel must survive for the design life (30 years) without maintenance, and they must be sufficiently cheap that the cost of the panel is quickly offset by the value of the energy that is captured.

Thermal systems are not viable as a substitute for conventional fossil-fuel power generation. For power generation direct conversion to electric power is more attractive.

Thermo-electric systems Two dissimilar metal wires, joined at one end, develop an emf (a voltage difference) TSV ∆=∆ between the two un-joined ends when the joined end is heated. S is the Seebeck constant, with units of volts/K, a characteristic of the materials of the couple. The technology can be used in combination with photo-voltaics to generate useful power from otherwise wasted heat.

The efficiency of a thermoelectric system depends on the materials that form the junction and the temperature difference between the junction and the free ends of the wires. It is measured by a figure of merit, Z:

λκeSZ

2

=

where eκ is the electrical conductivity, and λ the thermal conductivity. This is more commonly expressed as the dimensionless figure of merit ZT by multiplying Z by the average temperature

2/)( 21 TTT += of the extremes of the wires. Greater values of TZ indicate greater thermodynamic efficiency. Values of ZT = 1 are considered high, but values in the 3–4 range are needed for thermoelectrics to compete with conventional power generation. Compounds of bismuth (Bi), selenium (Se), tellurium (Te), ytterbium (Yb), and antimony (Sb) have the highest values of TZ but none as high as 4. These are materials with small reserves and localized sources, making large scale deployment of thermo-electric generation problematic.

Photo-voltaic (PV) systems Although photo-voltaic power is expensive, world capacity is growing rapidly, spurred on by ambitious targets for renewable contributions to electricity generation. In remote locations where transmission costs are high, solar power can compete with power from fossil fuels. But, as Figure 4 showed, it is capital and energy intensive to build.

The semiconductor that forms the active element of a PV collector has an energy gap (the gap between the conduction band and the valence band) comparable with the energy of the sun’s photons. Solar radiation arrives as photons with wavelengths λ between 0.3 and 3 microns, peaking at 0.5 microns. The corresponding photon energy is λ/ch (here h is Planck’s constant, 6.6 x 10-34 J/sec and c is the velocity of


Figure 12: A silicon-based photo-voltaic panel.

Figure 13: Demand ratios for strategic materials used in photo-voltaic power systems.

light 3 x 108 m/sec). If an electron with a charge e absorbs a photon it acquires a higher electric potential echV λ/=∆ . For solar photons,

V∆ is between 0.5 and 2.5 volts. If the energized electron now flows through an electric circuit across this potential difference it can deliver electrical energy to an external load.

Most photo-voltaic cells today use silicon as the semiconductor (Figure 12). A base layer of p-type silicon is joined to a thin emitter layer of n-type silicon that is exposed to the sun’s rays, which are absorbed in a layer near the p-n junction. The n-layer is doped with electron donors (5-valent elements such as phosphorous or arsenic) that readily give up an electron. The p-layer is doped with electron receptors (3-valent elements such as boron or gallium) that readily accept an electron, creating an electron “hole”. The mobile electrons in the n-layer and mobile holes in the p-layer provide charge carriers that allow an electric current to flow through the cell. At the p-n junction a potential difference exists because of the excess electrons on one side and holes on the other. When solar photons with an energy greater than the band gap penetrate this junction they create electron-hole pairs. The electrons move to

the negative electrode and the holes to the positive one to provide the current in the external circuit.

Only a fraction of the incoming solar energy is captured because long-wavelength photons have too little energy to create electron-hole pairs and are simply absorbed as heat; short wavelength photons have more than is needed and the difference, again, is absorbed as heat. The result is that the efficiency of conversion is low and it is reduced further if the panel does not face the sun but lies at an angle to it. Static thin-film devices made of amorphous silicon are the cheapest and give an efficiency of 8–9%. Poly-silicon crystals have efficiencies of 12–14%. Single crystal silicon cells (the most expensive) provide an efficiency of 15–17%, though they are energy-intensive to make. The average output is increased further by tracking the panels so that they face the sun continuously, allowing up to 20% conversion efficiency. Concentrators in the form of lenses or mirrors can improve the efficiency further. Newer systems use cadmium telluride (CdTe) or copper selenide Cu(In,Ga)Se2 semiconductors.


Figure 14: A wind turbine (Figure developed from a diagram of the US Department of Energy,

www1.eere.energy.gov/windandhydro).

Figure 15: Demand ratios for strategic materials used in wind power systems.

Once installed, solar PV power is effectively carbon-free. Although conversion efficiency declines over time, it requires little maintenance and has a long life. The difficulty with solar power in temperate climates is the low capacity factor, about 10%. This is because the rating of a panel (1 kW for example) is the power it produces when the incoming solar power density is 1000 W/m2, a value only reached at midday on a completely clear day. The average incoming power density, allowing for hours of darkness, cloud cover and other factors, is about 100 W/m2. This low capacity factor drives up the capital and material intensities and stretches the energy pay-back time to between 3 and 10 years (Figures 4 and 5). When installed in a dry, tropical location the capacity factor increases by three-fold or more, with a proportional drop in these intensities and times.

A bill of materials for a typical PV system is given in the Appendix (details vary with panel type and manufacturer). Many of these, such as indium, gallium, selenium, tellurium, and silver, are critical (Figure 13). A major expansion in photo-voltaic power generation would put their supply under pressure. Current research focuses on cheaper, more plentiful alternatives such as copper or iron sulfides.

6. Wind power Wind has been used as a source of power for centuries. Today wind turbines are the fastest-growing sector of the renewable power business. Currently 2% of global energy is generated through wind with global capacity doubling every three years. The problem with wind power, like that of most other renewable energy sources, is the low power density, that is, power per unit area.


On land, it averages 2 W/m2; off-shore it is larger, about 3 W/m2. The average land area per person averaged across a country with a population density like that of the UK is about 3500 m2. That means that if the entire country were packed with the maximum possible number of wind turbines, it would generate just 7 kW per person. Placing them off-shore helps solve the overcrowding problem, but maintenance costs are high.

When wind comes into contact with the rotor of a wind turbine, some of its kinetic energy is imparted to the blades, driving their rotation (Figure 14). This rotation is transmitted through a gearbox to a generator, creating electricity. The blades, made from laminated wood, GFRP or CFRP, carry both wind loads and self weight, requiring that they be light, stiff and strong. Motors in the nacelle of the turbine control pitch and yaw.

Wind speed v increases with height h above ground level:

( )14.0

10 10

≈

hvhv

where 10v is the wind speed at a height

m10=h . Very roughly, increasing the height of a wind turbine by a factor of two increases power by 30%, since power depends on wind speed cubed, as we show in a moment. Wind turbines have a cut-in and cut-out wind speed (typically 3 m/s2 cut-in and 20 m/s2 cut-out) to prevent damage.

The maximum power generated by a turbine is limited to 58% of the kinetic energy of the wind stream passing though it (the Betz limit, BC ). It is calculated by considering mass and energy conservation across the turbine, shown in Figure 16. Here the approaching wind velocity is 1v , the exit velocity is 2v , the swept area is S , and the mean velocity in the plane of the turbine is )( 212

1 vvv += . The energy flux per second (power) of an uninterrupted air flow of velocity 1v across an area S is:

31

211

21 2

1)(21

21 vSvvSvmPin ρρ ===

where ρ is the density of air, assumed constant and m is the mass per second passing through S . Thus input power increases with the cube of the velocity.

Figure 16: Control volume across a wind turbine.

Flow in an ideal (non-viscous) incompressible fluid is governed by Bernouilli’s equation:

constant21 2 =++ hgvp ρρ

where p is the pressure, v the flow velocity, g the gravitational constant, and h the height. Thus the pressure difference p∆ across the turbine caused by the drop in flow velocity from

1v to 2v at constant h is:

)(21 2

221 vvp −=∆

The air velocity in the plane of the turbine is v so the work done by p∆ per second, and thus the power P delivered to the turbine, is:

)()(41 1

22121 vvvvSvSpP −+=∆= ρ

The power coefficient is found by dividing this by the kinetic energy per second of the uninterrupted air flow passing across an area S giving:

−+=

2

1

2

1

2 1)1(21

vv

vv

PP

in

The maximum value of this ratio is the Betz limit, BC . Differentiating and equating to zero to

find the maximum gives the value BC = 0.59. The peak (rated) power of a turbine thus varies as the swept area S times the cube of the incoming wind speed 1v :

31

31 3.0

21 vSvSCPCP BinB ρρ ≈==

The power rating of a wind turbine (e.g. 2 MW) is its peak power. The actual power output depends on its capacity factor, the fraction of the peak power generated on average over a year, and this depends on turbine design and location. Off-shore turbines can achieve a capacity factor of 50% but they are expensive to build and maintain. The average capacity factor for land-based turbines is closer to 25% but they use less material, are cheaper to build, and easier to service.


Figure 17: Demand ratios for strategic materials used in hydro power systems.

Wind energy is free, but harvesting it is not. There is an energy investment cE associated with the construction of a wind turbine. The energy pay-back time bpt − required to return this energy

depends on the amount of energy gE generated by the turbine over a year:

g

cbp E

Et =−

Figure 5 showed that this, typically, is one to two years. The problem with wind power is not energy pay-back time but the small power output per unit. Even with an optimistic capacity factor of 50%, about 1000 2 MV-wind turbines are needed to replace the power output of just one conventional coal-fuelled power station, so the capital intensity, and that of land and materials is high (Figure 3 and Figure 4).

The drive to ever longer blades places constraints on the choice of materials. The self-weight of the blade creates alternating bending loads at the blade root as the turbine rotates. Superimposed on these is an axial load caused by centrifugal force. Both are best carried by materials with the largest values of the material index ρσ /y ,

where yσ is the yield strength and ρ the density Woods and GFRP perform well. Best of all is CFRP, making it the material of choice for the blades of large wind turbines.

The resource-demand ratios for critical materials appear in Figure 15. Both that for CFRP, the blade material, and for neodymium, a component of the permanent magnets of the generator, far exceed current production capability. It may be necessary to find substitutes for both.

7. Hydro power More energy is generated from hydropower than from any other renewable energy source. It supplies nearly all of the electricity for thirteen countries, including Norway and Brazil (IEA, 2000). The technology is simple, the power is always available (provided it rains), and dams built without hydroelectric capacity can be retro-fitted with turbines and generators. Lifetimes can exceed 100 years and the technology is mature, making it a safe investment, and the increase in material demands for large scale implementation are manageable (Figure 17).

The water-wheel provided power for irrigation and milling until the Industrial Revolution triggered its replacement by steam. Today, small water turbines produce electricity for local consumption. Large dams (Figure 18) create reservoirs for water that store enough energy to power entire cities. Hydro plants are particularly flexible because they both store energy and generate power, either continuously or intermittently to deal with spikes in demand.

The energy to fill reservoirs comes from the sun, but it is gravity that drives the water through the turbine. The flow of water through a water turbine, like that of air through a wind turbine, is governed by Bernoulli’s equation. When the water flow is from an essentially stationary reservoir to an essentially stationary out-flow pool, the equation reduces to hgp ∆=∆ ρ , where h∆ is the difference in surface height between the reservoir and the out-flow pool. The power captured by the turbine is then:

hQgP ∆= η

where Q is the volumetric flow rate in m3/s and η is the efficiency of the system (over 90% for large hydro plants and roughly 50% for small, (EST 2003)). The capital cost of a hydro plant can


Figure 18: Diagram of a hydroelectric dam.

be high, and its construction may damage natural and human habitat. But its lifetime is long, it requires little maintenance, it creates no emissions, and its fuel is free. It is a long-term investment.

8. Wave Power Energy can be captured from waves by placing something in their path. For instance, a fixed barrier with a turbine driven by the water whooshing in and out. Waves carry an energy per unit length rather than an energy per unit area. This is large: as much as 40 kW per meter. Capturing it, however, is not easy: it is unlikely that any wave machine would trap more than a third of this. Few countries have long coast-lines (some have none). However, for those that do, wave power is an option. But once again the scale of the operation has to be vast to make a real contribution: to provide 1 kW per person to a country of 50 million inhabitants needs 3,700 km of barrier. And any wave-driven device takes a considerable battering; maintenance is a problem.

There are three basic designs of wave-energy converters, and three options for siting them. Machines can be designed to generate electricity onshore, capturing the power of waves as they advance onto land. They can be moored near-shore allowing easy access. Or they can be sited offshore, where the higher waves increase capacity, but survivability is more of an issue (Scarr et. al., 2001).

The three schemes for harvesting wave power are know as buoyancy and hinged contour devices, overtopping devices, and oscillating water-column devices. The first uses the motion of waves to pump a working fluid through a turbine. Overtopping devices use a vertical axis turbine with a floating ramp; waves ride up the ramp and

spill into the turbine below. Oscillating water-column devices trap water and air within the structure. As the waves pass under it, the air is alternately compressed and allowed to expand through a turbine. Two of the more-developed designs are described below. Both are examples of hinged contour devices.

The total world installed capacity of wave power is currently a mere 4 MW but many devices are under development.

Pelamis The Pelamis buoyancy wave energy converter (Figure 19) is the most recognizable of wave technologies. The bulk of the machine floats on the surface, with cables securing it to the seafloor. Links in the body allow it to flex with the motion of the waves, driving pistons that pump oil through a turbine inside the unit. To survive the harsh environment the Pelamis uses a great deal of steel, making it material and energy intensive to construct. Studies are underway to reduce both intensities.

Oyster The Oyster wave energy conversion system is a near-shore device with most of its electricity generating equipment sited on land. It uses a flap device and the horizontal motion of the waves to pump water ashore, where it drives a turbine to generate electricity. In extreme conditions, the machine ducks under the water to avoid the strongest waves, so it does not need to be shut down. The name refers to the opening and closing mechanism by which it creates pumping pressure. The advantage of the design is its simplicity and ease of maintenance. The material intensity of the systems is kept low by allowing multiple Oysters to link to a single generator.


Figure 19: Schematic of Pelamis wave-power device.

The demand for critical materials for harvesting wave power is relatively low with the exception of copper. The small power per unit, and the long cables connecting them to shore means that building sufficient capacity to generate 2,000 GW over the next ten years could consume 20% of current production.

9. Tidal Power The moon orbits the earth and the earth orbits the sun. As they do so, gravitational and centrifugal forces act on seawater, pulling it into tidal bulges. As the Earth rotates on its own axis, these bulges sweep across the planet’s surface creating two tides each day. When sun, Earth and moon are aligned the forces work in conjunction, creating particularly high and low “spring” tides. When the moon is at right angles to the sun with respect to the Earth, the gravitational fields work against each other giving smaller “neap” tides. Since the moon orbits the Earth approximately once a month, there are two spring and two neap tides in this period.

The highest tidal range in the world is in the Bay of Fundy in Nova Scotia, Canada, where tidal water funnels into a narrowing channel. The same effect creates high tides in the Severn Estuary in Britain, a prime location for tidal power. Both tides are reinforced by tidal “resonance”: the reflection of tidal water from one coastline to another coinciding with the tidal pattern. Tidal power where tides are high can deliver 3 W/m2 by making both the incoming and the outgoing tidal flow drive turbines. This is about the same as wind power, but few countries are in a position to capture much of it. To those with tidal estuaries or at the mouths of large land-locked seas (like the Mediterranean) harnessing tidal power is an

option. But it is not one that will, by itself, provide all the energy as we need.

Tidal stream power–Seagen A Seagen tidal power generator is an underwater wind turbine (Figure 20). When the ocean becomes particularly turbulent or the machine needs maintenance the cross arms are lifted clear of the water by a hydraulic jack. The first Seagen is located in Strangford Lough, in Northern Ireland, UK. Table 3 shows the vital statistics of this machine. Tidal stream farms are still in the prototype and development stages, however much of the technology can be drawn from the marine, offshore, and the wind turbine industries.

Rated power 1200 kW

Capacity factor 48 %

Lifetime 20 years

Overall efficiency 89 %

Cut-in speed 0.7 m/s

Cut-out speed 2.25 m/s

Table 3: Statistics for the Seagen tidal power generator.


Figure 20: A Seagen tidal power generator.

Tidal barrage power A tidal barrage works in the same way as hydroelectricity and uses essentially the same equipment. A dam traps water as the tide rises, later releasing it through a turbine to generate electricity. The largest tidal barrage is the 240 MW unit on the river La Rance in France, where the tidal range is 8 m. The lifetime of tidal barrages is longer than that for tidal stream technologies because the machinery is less complicated and more mature.

As with wave power, demand for critical materials for harvesting wave power is relatively low with the exception of copper. The small power per unit, and the long cables connecting them to shore, means that building sufficient capacity to generate 2,000 GW over the next ten years could consume 5% of current production. Because the tidal range is small, tidal power is more capital and material intense than hydro power.

The attraction of tidal power is that, unlike wind, wave, and solar power, it is completely predictable. The drawback, as Figures 3, 4 and 5 show, is that its construction is material, energy and capital intensive.

10. Geothermal power The core of the Earth remains at a temperature above 5000ºC, heated by the slow radioactive decay of elements at its centre. Heat is carried to the Earth’s surface by conduction and by convection of the magma in the mantle, the layer between the core and the crust. This heat leaks out at the surface but little of it is in a useful form.

On average the near-surface temperature gradient is 20oC/km, delivering 50mW/m2 at the surface. To generate electricity it is necessary to heat water to at least 200oC, and for most of the earth’s crust that means drilling down to about 10 km making it expensive to harvest. Where magma wells up close to the surface the gradient rises above 40oC/km. In such places geysers and hot springs are generated where aquifers exist below the surface. Where this is so (Iceland, hot springs in the US, New Zealand, and elsewhere) extracting geothermal heat is a practical proposition.

To do so, water is injected into the hot rock from which it is recovered as hot water or steam (Figure 21). High-temperature plants feed steam directly to a turbine, then pump the condensate back into the rock. Low temperature plants pass the hot water to a heat exchanger where it vaporizes a working fluid, commonly isopentane or isobutane, that drives the turbine. Typical flow rates for the fluid are 75-100 kg s-1 and power outputs 0.1 to 2 GW. Geothermal power is renewable only if used sustainably. Current geothermal plants are pumping heat out faster than it is being replaced from below. At current capacity, the sites in Iceland, for example, will last about 100 years. As the best sites are exhausted, new, less good ones have to be exploited.

The cost of a geothermal power plant is primarily in the construction of the plant and the locating and drilling of the wells. The higher the near-surface temperatures, the lower the cost of drilling, and therefore the cheaper the plant. Aside


Figure 21: Geothermal power plant.

Figure 22: Soybean crop in Ohio, USA.

from the small cost of maintenance, the electricity it supplies is free. As with wave and tidal power, the only critical material used in large quantities is copper. Using the same demand structure as before, the deployment of 200 GW per year of geothermal power (could it be found) would require about 2% of current copper production

11. Biomass Green plants (Figure 22) capture the sun’s energy and use it to photosynthesize carbohydrates, oils and proteins from atmospheric CO2. The carbohydrates can be dried and burned to release the energy, or they can be fermented to give olefins (methane, ethane) and alcohols (methanol, ethanol) that can be used as fuels. Seed oil (soybean, sunflower, palm oil) can be burnt or

processed into bio-diesel. Plant growth requires little fossil fuel energy, is relatively clean, and–until it is burnt–it sequesters carbon. But the efficiency of energy-capture by plants is low, typically 0.5%. The average annual flux of solar radiation in a temperate climate is about 100 W/m2, so the area-intensity of biomass, before it has been converted to a useful fuel, is about 2000 m2/kW. This is already greater than that of any other source of power and it is not yet in useful form. Allowing for the inefficiencies and energy-penalties of drying or fermentation to bio-diesel the useful energy density falls and the area intensity rises to 5,000–10,000 W/m2.


Biomass as a source of power

The simplest way to use biomass is to burn it. It is said to be a carbon-neutral fuel because the carbon dioxide it emits when burnt was drawn from the atmosphere during its growth. But this is not quite true because farming and transport generates some CO2. To minimize this, dedicated biomass plants use local fuel sources but are small and unable to exploit the economies of scale (in respect to both cost and energy) of other power systems. Co-firing power plants use solid biomass to supplement coal, or methane to supplement gas, reducing dependency on imported fuels and providing a bridge from fossil to renewable energy generation.

Land farmed for biomass production is arable land that could be used to grow food instead. The competition with food production can be avoided by cultivating algae (marine plant-life) in farms offshore, which can either be dried and burned or fermented for biofuels. Table 4 shows the energy densities of several common biofuels. Oilseed and barley are the crops which contain the most energy and therefore are the most efficient grains to plant.

Crop kg/kW

Barley 0.19

Wheat 0.21

Oilseed grain 0.14

Woodchip 0.29

Woodpellet 0.20

Table 4: Energy densities of common biofuels.

The resource-demand ratios for materials to create and run a bio-fuel plant are relatively low, comparable with those for conventional gas or coal-fired power stations.

12. Summary and conclusions If the world is to have the electrical power that extrapolation suggests will be needed in 2050, it may mean building an additional generating capacity of 12,000 GW. The power available from natural resources is very large. The global flux of solar, wind, wave, and tidal energy each comfortably exceed this. The estimates for the accessible coal and nuclear fuel, might also meet it, if properly managed. But each has its difficulties and even a balanced combination of all presents problems.

All renewable power systems carry a carbon footprint, that is 10 to 30 times less than the gas and oil based systems on which we now largely depend. But almost all require greater surface area and it takes more capital and energy to construct the same nominal generating capacity. Worse, most have a lower capacity factor (the fraction of life over which they operate at full capacity). The exception is geothermal power: wonderful if you’ve got lots of it, but few countries have.

A high material intensity would be manageable if the material in question were one with large reserves and low embodied energy and carbon footprint. Some materials meet this ideal: iron and carbon steel, concrete, wood, and commodity polymers. The resource demand plots have assumed that one sixth of the predicted 2050 energy requirements will be met over a period of 10 years from new installations providing an additional 200 GW of power per year. But the sheer scale of this demand would put pressure upon material supply, greatly exceeding the current production capacity of the scarcer ones.

The conclusions: no single renewable source can begin to supply energy on the scale we now use it. A combination of all them might. But think of the difficulties. There is the low power density, meaning that a large fraction of the area of the country must be dedicated to capturing it. If you cover half the country with solar cells you cannot also plant crops for biofuel on it, nor can you use it as we now do for agriculture and livestock for food. There is the cost of establishing such a dispersed network and–in the case of off-shore wave and wind farms–of maintenance (even on land some 2% of wind turbines are disabled each year by lightning). And there is the opposition, much of it from environmentalists, that paving the country and framing the coast with machinery would create. MacKay’s (2008) book examines all this in greater depth; for now we must accept that the dream of copious cheap, pollution-free energy from sun, wind and wave, is not going to become a reality.


13. Appendix: Approximate material intensities for power systems

Bills of materials for the power systems are assembled here. They are expressed as material intensities, mI , meaning the mass (kg) of each materials per unit (kW.hr) of nominal generating capacity. There is no systematic, self-consistent assembly of such data of which we are aware, so it has to be patched together from diverse sources. These differ in detail and scope. Some, for instance, are limited to the system alone, others include the copper and other materials needed to connect the system to the grid, large for distributed systems like wind, wave and solar power. Others give indirect information from which missing material content can be inferred. So be prepared for inconsistencies.

Despite these there is enough information here to draw conclusions about the demand that a commitment to any one of them will put on material supply. The resource-demand plots in the text use the data in these tables. They are based on an imagined scenario: that the global electric power demand in 2050 will be 6,000 GW (three times that of now, 2010) and that to meet it the capacity of a chosen system has is expanded by 200 GW (equal to 2 x 108 kW) per year, which, allowing for retirements in the intervening 40 years, will provide about the expected demand. The metric for resource pressure sR is the mass of each material required for the expansion of the system per year, mI8102× , expressed in kg/year divided by the current (2008 – the most recent available) global production per year, aP , also expressed in kg/year.

a

ms P

IR

××=

8102

The plots show this as the per-cent demand of current production.

The resource demand is not interesting when it is trivial. The plots show the demand on the materials that are deemed to be “critical”, as explained in Section 2. Their global annual production in 2008 appears in Figure 7. They are starred (*) in the tables below.

Coal-fired station

Material Intensity (kg/kWnom)

Aluminum 2.58–4.5

Bitumen 0.33–0.37

Brass 0.24–0.27

Carbon steel 30–614

Ceramic tiles 0.39–0.44

Chromium* 2.33–3.2

Concrete 460–1200

Copper 1.47–5.17

Epoxy 0.21–0.23

GFRP 0.55–0.605

Glass 0.026–0.029

Glulam 0.004–0.005

HDPE 0.16–0.17

High alloyed steel 0.5

Iron 50.2–809

Lead 0.04–0.23

Low alloy steel 13.6–15.1

Manganese * 0.084

Molybdenum* 0.032

Nickel 0.01

PP 0.08–0.09

PVC 1.82–2.02

Rock wool 3.9–4.3

Rubber 0.12–0.13

SAN 0.026–0.031

Silver* 0.001–0.007

Stainless steel 37–41

Vanadium* 0.003

Zinc 0.06–0.08

Total mass, all materials 520–1800

Materials and quantities from White and Kulcinski (2007).


Wind power, off shore


Aluminum 0.85–15 Carbon steel/cast iron 380–532 CFRP* 10.5–54 Cobalt* (alternative magnets)

1

Concrete 1200–1600 Copper* 10–22 GFRP 14–20 Neodymium* (magnets) 0.9 Polymers 0.7–9 Stainless steel 36–50 Total mass, all materials 1100–2000 Materials and quantities from Vestas (2008) and Martinez et al (2007).

Wind power, land-based


Aluminum 0.85–15 Carbon steel/cast iron 273–350 CFRP* 10.5–54 Cobalt* (alternative magnets)

Concrete 360–800 Copper* 0.84–8 GFRP 14–20 Neodymium* (magnets) 1 Polymers 0.7–9 Stainless steel 36–50 Total mass, all materials 200–600 Materials and quantities from Vestas (2008) and Martinez et al (2007).

Photo-voltaic power Material Intensity

(kg/kWnom) Aluminum 62.32 Antimony (dopant) 0.10 Copper* 0.8 EVA 41.33 Gallium* (dopant) 0.50 Galvanized mild steel 40.67 Indium* 0.08 Lead tin solder 0.08 Silane (amorphous silicon)

0.49

Silver* 0.08 Stainless steel 18.70 Tellurium* (dopant) 0.10 Ytterbium* (dopant) 0.10 Total mass, all materials

100–220

Materials and quantities from Keoleion et al (1997) and Tritt et al (2008).

Pressurized water reactor Material Intensity (kg/kWnom)

Aluminum 0.02–0.24 Boron 0.01 Brass/bronze 0.04 Cadmium 0.01 Carbon steel 10.0–65 Chromium* 0.15–0.55 Concrete 180–560 Copper* 0.69–2 Galvanized iron 1.26 Inconel 0.1–0.12 Indium* 0.01 Insulation 0.7–0.92 Lead 0.03–0.05 Manganese* 0.33–0.7 Nickel* 0.1–0.5 PVC 0.8–1.27 Silver* 0.01 Stainless steel 1.56–2.1 Uranium* 0.4–0.62 Wood 4.7–5.6 Zirconium* 0.2–0.4 Total mass, all materials

170–625

Materials and quantities from White and Kulcinski (2007).


Geothermal power


Bentonite 20.9–45 Calcium carbonate 37.9 Carbon steel 10.8 Cement 3.3–41 Chalk 31 Concrete 21.9 Copper* 1.2–2.2 EVA 1 High alloy steel 342.4 LDPE 20.4 Low alloy steel 2–476 Portland limestone cement

133

PVC 0.1 silica sand 39.6

Total mass, all materials

61–1200

Materials and quantities from Saner et al (2010)

Tidal barrage power


ABS 30% glass fiber 0.019 Cement 1728 Copper* 0.004 Gravel 996 Pre-stressed concrete 3416 Rock 28686 Sand 20488 Stainless steel 0.026 Steel 33 Total mass, all materials

55,350

Materials and quantities from Roberts (1982) and Miller et al (2010)

Tidal current power: Seagen


CFRP (blades) 3.25 Copper* 3.88 Epoxy 0.25 GFRP (enclosure) 4.5 Iron 28.3 Neodymium or cobalt 0.9 Stainless steel 2.33 Steel 344 Total mass, all materials

387

Materials and quantities from Douglas et al (2008).

Wave power Material Intensity (kg/kWnom)

Aluminum 25–30 Copper* 10–20 Nylon 6 8–12 Polyurethane 12–18 PVC 25–31 Sand (ballast) 640 Stainless steel 50–60 Steel 410 Total mass, all materials 1145–2000

Materials and quantities from Anderson (2003).

Hydro power Material Intensity (kg/kWnom)

Aluminum 0.76–5.81 Brass 0.09 Carbon steel 13.48–792 Chromium* 2.19–2.47 Concrete 3927–5869 Copper* 0.18–14.6 Iron 14.1–564 Lead 0.06–1.04 Manganese * 0.33–2.44 Molybdenum* 0.0005 Nickel based alloys * 0.06–0.43 Plastics 1.46–5.74 Silica 2.11–25 Silver* 0.0007 Stainless steel 1.95–19.2 Stone 321–410 Tin 0.0004–0.001 Titanium dioxide* 0.04 Wood 120 Zinc 0.07–4.73 Total mass, all materials 891–5741

Materials and quantities from Ribeiro et al (2010) and Vattenfall (2008).


Biomass


Aluminum 1.1–6.7

Bitumen 0.5

Brass* 0.37

Cast iron 1.47

Ceramic tiles 0.59–9.3

Chromium* 0.0024

Cobalt* 0.0018

Concrete 36–790

Copper* 1.04–3.5

Epoxy resin 0.31

GFRP 0.82

Glass 0.04

Glulam 0.006

HDPE 0.23

LDPE 3.25

Lead 0.104

Low alloy steel 20

Low carbon steel 33–112

Nickel* 0.02

PP 0.12

PVC 0.45–2.74

Rock wool 1.65–6

SAN 0.04

Stainless steel 4.5–5.5

Steel (electric) 0.82

Synthetic rubber 0.18

Titanium dioxide* 0.4

Zinc 0.16

Total mass, all materials

69–922

Materials and quantities from Bauer (2008) and Mann and Spath (1997)


14. Appendix: Definitions Keeping track of units and the meanings of the various resource intensities can be a bit confusing. The definitions on these pages will help keep them clear.

Energy and power Energy MJ or kW.hr (1 kW.hr = 3.6 MJ)

Energy appears in more than one form in this White Paper. It is important to choose one of these as the basis for comparison of conventional and renewable systems. By convention, the basic unit is MJoe, meaning megajoules, oil equivalent. Oil (like coal and gas) has a calorific value or heat content, 38 MJoe/litre or 44 MJoe/kg. The conversion efficiency when oil is used to generate electricity is about 36% (it depends on the age and type of generator), so one MJ of electrical energy (MJelec) requires the consumption of 1/0.36 = 2.8 MJoe. Thus 1 kW.hr of electrical energy is equivalent to 3.6 x 2.8 = 10 MJoe.

Power kW, MW or GW Power is energy per unit time, meaning J/sec (= Watt, W) or, in the context of power systems, kW, MW, GW or even TW (Terawatt = 1012 J/sec)

Rated or nominal power output kWnom, etc The rated power output of a power system is the power it delivers under optimal conditions. Oil and coal fired power stations operate optimally for much of the time, but renewable power systems do not because they depend on a certain minimum level of solar radiation, wind velocity, wave height or tidal flow, and for much of the time this minimum is not met.

Actual / real average power output kWactual, etc The optimal conditions required for a power system to provide its rated power occur for only a fraction of the time, so the actual power output of the system, averaged over (say) a year, is much less than the rated value. The ratio of the real, averaged power output to the rated power output is called the capacity factor, expressed as a %. Some systems have capacity factors as low as 10%, meaning that to generate 1 kW of power it is necessary to install a system with a rated capacity of 10 kW.

Resource intensity Resource intensities

Construction and commissioning of a power system requires resources: capital, materials, energy and space, meaning land or sea area. A resource intensity is the amount of the resource required to create one unit of power generating capacity. Power systems have a rated power (kWnom, see above), but none operate at full

capacity all the time so it is convenient to define also the average delivered power (kWactual). Because of this we need two intensities for each resource. The first is the intensity of the resource per unit of rated capacity – a well defined quantity since the rated power is a fixed characteristic of the system (e.g. a 1 kW solar panel). The second is the intensity of the resource per unit of delivered power when averaged over a representative period such as a year. It is always larger, sometimes much larger, than the intensity per unit of rated capacity, and it is less well defined because it depends on how the system is operated, and, in the case of renewable systems, on the influence of the weather on sun, wind, wave and tide.

Capital intensity, GBP/kWnom construction (rated power)

The quantity of capital (money) used to construct the power system per unit rated power (per kWnom, for example) of the system. If you want the cost per kW of actual delivered power, as in Figure 4, you have to divide the capital intensity by the capacity factor (expressed as a fraction).

Capital intensity (fuel) GBP/kW The cost of the fuel used in the system per kW of power generated. This is based on input/output figures from plants and scaled to be a nominal value.

Area intensity m2/kWnom

The land area used by the power system per unit rated power (kW) of the system. If you want the area per kW of actual delivered power capacity, as in Figure 3, you have to divide the area intensity by the capacity factor (expressed as a fraction).

Material intensity kg/kWnom

How much materials are used in total in kilos to create the power system per unit rated power (kW) of the system. If you want the material per kW of actual delivered power, as in Figure 3, you have to divide the material intensity by the capacity factor (expressed as a fraction).

Energy intensity (construction) MJ/kWnom

The energy is used to construct the power system, per unit rated power (kW) of the system. To get the build-energy per kW of actual delivered power, you have to divide the energy intensity by the capacity factor (expressed as a fraction). This is not done in Figure 5 because the other axis, delivered energy per year, is also nominal. The point of Figure 5 is to illustrate the pay-back time.

Energy intensity (fuel) MJ/kW How much energy is consumed as fuel by the power system to generate each kW of power. This is based on input/output figures from plants, scaled to be a nominal value.


CO2 intensity (construction) kg/kWnom

How many kilos of Carbon dioxide are produced as the power system is constructed per unit rated power (kWnom) of the system. This is a nominal value calculated assuming a 100% capacity factor.

CO2 intensity (fuel) kg/kW

How many kilos of carbon dioxide are produced by producing, transporting and using the fuel used in a particular power system per kW of power produced by the system. This is based on input/output figures from plants, scaled to be a nominal value.

Operational parameters Capacity factor %

The fraction of time, expressed as a percentage, that a power system operates at its rated power. This takes into account time when a system would be unavailable or generating less power than it potentially could due to maintenance or because the natural resource it uses is unavailable.

System efficiency % The efficiency with which the fuel or resource is converted into electricity.

Lifetime yrs The expected time that the power system will remain fully operational in years.

Status Current installed capacity GW The total global rated capacity of a given power system.

Growth rate %/year

The rate at which installed capacity currently grows each year expressed as a percentage.

Delivered cost GBP/kWh

The cost of generating one kilowatt-hour of electrical energy for a given power system.


15. Appendix: Further reading

The starting point–sources that help with the big picture. Andrews, J. and Jelley, N. (2007) “Energy science: principles, technologies and impacts”, Oxford University Press, Oxford, UK. ISBN 978-0-19-928112-1. (An introduction to the science behind energy sources and energy storage systems.)

Boyle G. (editor) (2004) “Renewable energy”, DE.158

Fay, J.A. and Golomb, D.S. (2002) “Energy and the environment”, Oxford University Press, Oxford, UK. ISBN 0-19-515092-9. (The environmental background to energy production, with an exploration of the potential for replacing fossil fuels by lower carbon alternatives.)

Harvey, L.D.D. (2010) “Carbon-free energy supply” Earthscan Publishing, London UK. ISBN 978-1-84971-073-2.

IAEA (1997) “Sustainable development and nuclear power”, International Atomic Energy Agency, Vienna, Austria.

IEA (2010) “International Energy Agency Electricity information 2008” OECD / IEA, Paris, France. ISBN 978-92-64-04252-0. (An extraordinarily detailed, annual, compilation of historical and current statistics on electricity generation and use.)

MacKay, D.J.C. (2009) “Sustainable energy–without the hot air” UIT Publishers, Cambridge UK. ISBN 978-0-9544529-3-3 and www.withouthotair.com. (MacKay takes a critical look at the potential for replacing fossil fuel base energy by alternatives. A book noteworthy for clarity of argument and style.)

McFarland, E.L., Hunt, J.L., Campbell, J.L.E. (2007) “Energy, physics and the environment”, Thompson Publishers, UK. ISBN 0-920063-62-4. (The underpinning physics for alternative power systems, and more.)

Meyer, P.J. (2002) “Life cycle assessment of electricity generation systems and applications for climate change policy analysis”, Fusion Technology Institute, University of Wisconsin, PhD Thesis (Report number UWFDM-1181). (Case studies of alternative power generating systems, making use of triangle-maps like that of Figure 2.)

San Martin, R.L. (1989) “Environmental emissions from energy technology systems: the total fuel cycle”, US Department of Energy, Washington DC, USA.

UK Department of Energy and Climate Change (2010) “Statistics” www.decc.gov.uk/assets/decc/Statistics

Coal and gas fired power CCSA (2010), “About CCS, Carbon Capture and Storage Association”, www.ccsassociation.org.uk (Accessed 08/10)

EPRI (2009), “Program on Technology Innovation: Integrated Generation Technology Options” Energy Technology Assessment Centre

Hondo, H. (2005) “Life cycle GHG emission analysis of power generation systems: Japanese case”, Elsevier, Energy Vol.. 30 pp. 2042–2056.

IEA (2002) “Environmental and Health Impacts of Electricity Generation”, www.ieahydro.org/reports/ST3-020613b.pdf (Accessed 08/10)

Kaplan, S., (2008) “Power Plants: Characteristics and Costs”, CRS Report for Congress, www.fas.org/sgp/crs/misc/RL34746.pdf (Accessed 09/10)

Mayer-Spohn, O., (2009) Parametrised Life Cycle Assessment of Electricity Generation in Hard-Coal-Fuelled Power Plants with Carbon Capture and Storage, Universitat Stuttgart, http://elib.uni-stuttgart.de/opus/volltexte/2010/5031/pdf/100114_Dissertation_Mayer_Spohn_FB105.pdf (Accessed 08/10)

Meier P.J. (2002) Life cycle assessment of electricity generation systems and applications for climate change policy analysis, University of Wisconsin, http://fti.neep.wisc.edu/pdf/fdm1181.pdf (Accessed 08/10)

National Grid (2010), “Calorific Value description”, www.nationalgrid.com/uk/Gas/Data/help/opdata (Accessed 08/10)

NaturalGas.org (2010), Overview of Natural Gas, http://naturalgas.org/overview/overview.asp (Accessed 09/10)

Stranges, A.N., (2010) Coal, Chemistry Explained, Advameg Inc, www.chemistryexplained.com/Ce-Co/Coal (Accessed 08/10)

White, S.W. and Kulcinski, G.L. (2000) “Birth to death analysis of the energy payback ratio and CO2 gas emission rates from coal, fission, wind and DT-fusion electrical power plants”, University of Wisconsin-Madison. Fusion Engineering and Design Vol. 48 pp.473–481.

Nuclear power Andrews, J. and Jelley N. (2007) “Energy science”, Oxford University Press, Oxford, UK. ISBN 978-0-19-928112-1

British Energy (2005), “Environmental Product Declaration of Electricity from Torness Nuclear Power Station”, www.british-energy.com (Accessed 08/10)

http://www.withouthotair.com/�

http://www.decc.gov.uk/assets/decc/Statistics�

http://www.ccsassociation.org.uk/�

http://www.ieahydro.org/reports/ST3-020613b.pdf�

http://www.fas.org/sgp/crs/misc/RL34746.pdf�

http://elib.uni-stuttgart.de/opus/volltexte/2010/5031/pdf/100114_Dissertation_Mayer_Spohn_FB105.pdf�



http://fti.neep.wisc.edu/pdf/fdm1181.pdf�

http://www.nationalgrid.com/uk/Gas/Data/help/opdata�

http://naturalgas.org/overview/overview.asp�

http://www.chemistryexplained.com/Ce-Co/Coal�

http://www.chemistryexplained.com/Ce-Co/Coal�

http://www.british-energy.com/�


Environmental Science and Technology. 42:2624-2630 http://ec.europa.eu/environment/integration/research/newsalert/pdf/109na4.pdf (Accessed 08/10)

Glasstone, S. and Sesonske, A. (1994) “ Nuclear reactor engineering” 4th edition, Chapman and Hall, New York, NY, USA. ISBN 0-412-98521-7.

Kaplan, S., (2008) “Power Plants: Characteristics and Costs”, CRS Report for Congress, www.fas.org (Accessed 09/10)

Rashad, S.M. and Hammad, F.H. (2000) “Nuclear poser and the environment: comparative assessment of the environmental and health impacts of electricity-generating systems” Applied Energy, Vol. 65, pp. 211–229.

Roberts, J.T.A. (1981) “Structural materials in nuclear power systems” Plenum Press, New York, NY, USA. ISBN 0-306-40669-1.

Storm van Leeuwen, J.W. (2007) “Nuclear Power–the energy balance”, Ceedata Consultancy, www.stormsmith.nl/report20071013/partF.pdf (Accessed 08/10)

Voorspools, K.R., Brouwers, E.A., D’Haeseleer, W.D. (2000) Energy content and indirect greenhouse gas emissions embedded in ‘emission-free’ power plants: results for the Low Countries, University of Leuven, Belgium. Applied Energy Vol. 67 pp. 307±330

White, S.W., and Kulcinski, G.L. (1998a) Birth to death analysis of the energy payback ratio and CO2 gas emission rates from coal, fission, wind and DT-fusion electrical power plants, University of Wisconsin-Madison. Fusion Engineering and Design Vol.48 (248) pp.473–481

White, S.W., Kulcinski, G.L., (1998b) “Energy Payback Ratios and CO2 Emissions Associated with the UWMAK-I and ARIES-RS DT-Fusion Power Plants”, Fusion Technology Institute, Wisconsin, http://fti.neep.wisc.edu/pdf/fdm1085.pdf (Accessed 08/10).

WISE Uranium project (2009), “Nuclear Fuel Energy Balance Calculator”, www.wise-uranium.org/nfce (Accessed 08/10)

World Nuclear Association, (2009) “Nuclear Power Reactors”, www.world-nuclear.org/info/inf32 (Accessed 08/10)

Solar power AMP Blogs network (2009), New Solar Panel Materials Studied, www.aboutmyplanet.com/alternative-energy/new-solar-panel-materials-studied/ (Accessed 08/10)

Ardente, F., Beccali, G., Cellura, M., Lo Brano, V. (2005) Life cycle assessment of a solar thermal

collector, University of Palmero, Italy. Renewable Energy Vol. 30 pp. 1031–1054

Bankier,C., Gale, S. (2006), Energy payback of roof mounted photo-voltaic cells, The Environmental Engineer www.rpc.com.au/pdf/Environmental_Engineer_Summer_06_paper_2.pdf (Accessed 08/10)

Blakers, A., Weber, K. (2000), The Energy Intensity of Photo-voltaic Systems, Centre for Sustainable Energy Systems, Australian National University www.ecotopia.com (Accessed 08/10)

Carbon Free Energy Solutions, (2010) Philadelphia solar modules, www.carbonfreeenergy.co.uk (Accessed 08/10)

Denholm, P., Margolis, R.M., Ong, S., and Roberts, B. (2010) Sun Gets Even, National Renewable Energy Laboratory, http://newenergynews.blogspot.com/2010/02/sun-gets-even.html, (Accessed 08/10)

Energy Development Co-Operative Limited, (2010) Solar Panels–Solar PV Modules, www.solar-wind.co.uk/solar_panels (Accessed 08/10)

Genersys Plc. (2007) 1000-10 Solar Panel Technical Datasheet www.genersys-solar.com (Accessed 08/10)

Ginley,D., Green, M.A., and Collins, R. (2008) Solar energy Conversion towards 1 Terawatt, MRS Bulletin, Volume 33, No.4.

Intelligent Energy Solutions, (2010) Solar Panel Cost www.intelligentenergysolutions.com (Accessed 08/10)

Kannan, R., Leong, K.C., Osman, R., Ho, H.K., Tso, C.P. (2005) Life cycle assessment study of solar PV systems: An example of a 2.7 kWp distributed solar PV system in Singapore, Elsevier.

Keoleian, G.A. and Lewis, G.McD. (1997) Application of life cycle energy analysis to Photo-voltaic Module Design, Progress in Photo-voltaic s: Research and applications, Vol.5 http://deepblue.lib.umich.edu (Accessed 08/10)

Knapp, K.E., Jester, T.L. (2000) An Empirical Perspective on the Energy Payback Time for Photo-voltaic Modules Solar 2000 Conference, Madison, Wisconsin.

Koroneos, C., Stylos, M., Moussiopoulos N. (2005) LCA of Multicrystalline Silicon Photo-voltaic Systems, Aristotle University of Thessaloniki.

Lewis, G.M., Keoleian, G.A. (1997), Life Cycle Design of Amorphous Silicon Photo-voltaic Modules, EPA www.umich.edu/~nppcpub/research/pv.pdf (Accessed 08/10)

http://ec.europa.eu/environment/integration/research/newsalert/pdf/109na4.pdf�

http://ec.europa.eu/environment/integration/research/newsalert/pdf/109na4.pdf�


http://www.stormsmith.nl/report20071013/partF.pdf�


http://www.wise-uranium.org/nfce�

http://www.wise-uranium.org/nfce�

http://www.world-nuclear.org/info/inf32�

http://www.world-nuclear.org/info/inf32�

http://www.aboutmyplanet.com/alternative-energy/new-solar-panel-materials-studied/�

http://www.aboutmyplanet.com/alternative-energy/new-solar-panel-materials-studied/�

http://www.rpc.com.au/pdf/Environmental_Engineer_Summer_06_paper_2.pdf�

http://www.rpc.com.au/pdf/Environmental_Engineer_Summer_06_paper_2.pdf�

http://www.ecotopia.com/�

http://www.carbonfreeenergy.co.uk/�

http://newenergynews.blogspot.com/2010/02/sun-gets-even.html�

http://newenergynews.blogspot.com/2010/02/sun-gets-even.html�

http://www.solar-wind.co.uk/solar_panels�

http://www.genersys-solar.com/�

http://www.intelligentenergysolutions.com/�

http://deepblue.lib.umich.edu/�

http://www.umich.edu/~nppcpub/research/pv.pdf�


Meier P.J. (2002) Life cycle assessment of electricity generation systems and applications for climate change policy analysis, University of Wisconsin, http://fti.neep.wisc.edu/pdf/fdm1181.pdf (Accessed 08/10)

Sanyo (2009), HIT photo-voltaic module www.shop.solar-wind.co.uk (Accessed 08/10)

Sharp (2008), ND Series, 210W/200W Photo-voltaic solar panels www.shop.solar-wind.co.uk/acatalog/Sharp_Solar_Panel_ND_210E1F_Brochure.pdf (Accessed 08/10)

Solar Systems, (2010) Projects, Mildura solar farm www.solarsystems.com.au/projects (Accessed 08/10).

Tritt, T.M., Bottner, H., Chen, L. (2008) Thermoelectrics: Direct Solar Thermal Energy Conversion, MRS Bulletin, Volume 33, No.4.

Vidal, J. (2008), World’s biggest solar farm at centre of Portugal’s ambitious energy plan, The Guardian, Environment, Renewable Energy www.guardian.co.uk/environment/2008/jun/06/renewableenergy.alternativeenergy (Accessed 08/10)

Woodall, B. (2006), World’s Biggest Solar Farm Planned for New Mexico, Planet Ark www.planetark.com/dailynewsstory.cfm/newsid/36162/story.htm (Accessed 08/10)

Wind power CF Hood, (2009), The history of carbon fibre, www.carbon-fiber-hood.net/cf-history (Accessed 08/10)

Crawford, R.H. (2009) Life cycle energy and greenhouse emissions analysis of wind turbines and the effect of size on energy yield, University of Melbourne, Australia, Renewable and Sustainable Energy Reviews Vol. 13, Issue 9, pp. 2653-2660.

Danish wind industry association, (2003) What does a Wind Turbine Cost?, http://guidedtour.windpower.org (Accessed 08/10)

EWEA, (2003) Costs and Prices, Wind Energy–The Facts, Volume 2, www.ewea.org (Accessed 08/10)

Hau, E. (2006) Wind turbines: fundamentals, technologies, application, economics, 2nd Edition, Springer, ISBN 3-540-24240-6.

Hayman, B., Wedel-Heinen, J., Brondsted, P. (2008) Materials Challenges in Present and Future Wind Energy, MRS Bulletin, Volume 33, No 4.

Martinez, E., Sanz, F., Pellegrini, S., Jimenez, E., Blanco, J. (2007) Life cycle assessment of a multi-megawatt wind turbine, University of La Rioja, Spain. www.assemblywales.org (Accessed 08/10)

McCulloch, M., Raynolds, M., Laurie, M. (2000) Life cycle Value assessment of a Wind Turbine, Pembina Institute, http://pubs.pembina.org/reports/windlcva.pdf (Accessed 08/10)

Musgrove, P. (2010) Wind Power, Cambridge University Press, ISBN: 978-0-521-74763-9

Nalukowe, B.B., Liu, J., Damien, W., Lukawski, T. (2006) Life cycle assessment of a Wind Turbine www.infra.kth.se/fms/utbildning/lca/projects (Accessed 08/10)

Vestas (2008) V82-1,65 MW, Vestas Wind turbine brochure

Weinzettel, J., Reenaas, M., Solli, C., Hertwich, E.G. (2009) Life cycle assessment of a floating offshore wind turbine, Renewable Energy, Elsevier Renewable Energy Vol. 34 pp.742–747

Windustry (2010), How much do wind turbines cost? Windustry and Great Plains Windustry Project, Minneapolis www.windustry.org/how-much-do-wind-turbines-cost (Accessed 08/10)

Hydro power Davies, J., Wright, M., Monetti, K., Van Den Berg, D., (2007) Hydroelectric Section of the Energy Task Force, www.investfairbanks.com/documents/Hydronarrative12-07.pdf (Accessed 09/10)

Energy Saving Trust (2003) Small Scale Hydroelectricity, www.savenergy.org (Accessed 09/10)

IEA (2000) Hydropower and the World’s Energy Future, www.ieahydro.org/reports/Hydrofut.pdf (Accessed 09/10)

Ribeiro, F de M., da Silva, G.A., (2010) Life cycle inventory for hydroelectric generation: a Brazilian case study, Journal of Cleaner Production, Journal of Cleaner Production 18 (2010) 44–54

Sims, R.E.H., Hydropower, Geothermal, and Ocean Energy, MRS Bulletin, Volume 33, No.4, April 2008.

US Department of the Interior, Bureau of Reclamation, (2008) Hoover Dam, Frequently Asked Questions and Answers, The Dam, www.usbr.gov/lc/hooverdam/faqs/damfaqs.html (accessed 08/10)

Vattenfall AB (2008), Certified environmental product declaration EPD of electricity from Vattenfall’s Nordic hydropower, www.vattenfall.com (Accessed 08/10)

Wave power Anderson, C., (2003) Pelamis WEC–Main body structural design and materials selection, DTI, http://webarchive.nationalarchives.gov.uk/tna/+/htt


http://www.shop.solar-wind.co.uk/�

http://www.shop.solar-wind.co.uk/acatalog/Sharp_Solar_Panel_ND_210E1F_Brochure.pdf�



http://www.solarsystems.com.au/projects�

http://www.guardian.co.uk/environment/2008/jun/06/renewableenergy.alternativeenergy�

http://www.guardian.co.uk/environment/2008/jun/06/renewableenergy.alternativeenergy�

http://www.planetark.com/dailynewsstory.cfm/newsid/36162/story.htm�

http://www.planetark.com/dailynewsstory.cfm/newsid/36162/story.htm�

http://www.carbon-fiber-hood.net/cf-history�

http://guidedtour.windpower.org/�

http://www.ewea.org/�

http://www.assemblywales.org/�

http://pubs.pembina.org/reports/windlcva.pdf�

http://www.infra.kth.se/fms/utbildning/lca/projects�

http://www.windustry.org/how-much-do-wind-turbines-cost�

http://www.windustry.org/how-much-do-wind-turbines-cost�

http://www.investfairbanks.com/documents/Hydronarrative12-07.pdf�

http://www.investfairbanks.com/documents/Hydronarrative12-07.pdf�

http://www.savenergy.org/�

http://www.ieahydro.org/reports/Hydrofut.pdf�

http://www.usbr.gov/lc/hooverdam/faqs/damfaqs.html�

http://www.vattenfall.com/�

http://webarchive.nationalarchives.gov.uk/tna/+/http:/www.dti.gov.uk/renewables/publications/pdfs/v0600197.pdf/�


p://www.dti.gov.uk/renewables/publications/pdfs/v0600197.pdf/

Carcas, M., The Pelamis Wave Energy Converter–A phased array of heave + surge point absorbers, Ocean Power Delivery Ltd.,

(Accessed 09/10)

Boronowski, S., Wild, P., Rowe, R., van Kooten, G.C., (2010) Integration of wave power in Haida Gwaii, University of Victoria, RenewableEnergy Vol.35 pp. 2415-2421

http://hydropower.inel.gov/hydrokinetic_wave/pdfs/day1/09_heavesurge_wave_devices.pdf (Accessed 09/10)

Energy Action Devon, (2010) Wave Power, Devon Association for Renewable Energy, www.devondare.org/wavepower (Accessed 09/10)

Henry, A., Doherty, K., Cameron, L., Whittaker, T., Doherty, R., (2010) Advances in the design of the Oyster wave energy converter, www.aquamarinepower.com/pub (Accessed 09/10)

Parker, R.P.M., Harrison, G.P., Chick, J.P., (2007) Energy and carbon audit of an offshore wave energy converter, School of Engineering and Electronics, University of Edinburgh.

Peak Energy (2010) Wave power potential in Australia, http://peakenergy.blogspot.com/2010/09/wave-power-potential-in-australia.html (Accessed 09/10)

Pelamis Wave Power, (2010) Environmental Characteristics www.pelamiswave.com (Accessed 09/10)

Wave Dragon (2005) Wave Dragon, www.wavedragon.net (Accessed 09/10).

Tidal power Douglas, C. A., Harrison, G. P., Chick, J. P., (2008) Life cycle assessment of the Seagen marine current turbine, Department of Engineering and Electronics, University of Edinburgh Proc. IMechE Vol. 222 Part M: J. Engineering for the Maritime Environment pp. 1–12.

Harvey, L.D.D., (2010) Energy and the New Reality 2, Carbon Free Energy Supply, Earthscan Ltd., London.

Miller, V.B., Landis, A.F., Schaefer, L.A., (2010) A benchmark for life cyc;e air emissions and life cycle impact assessment of hydrokinetic energy extraction using life cycle assessment, Renewable Energy, Elsevier, Renewable Energy Vol 35, pp. 1-7

Roberts, F., (1982) Energy Accounting of River Severn Tidal Power Schemes, Applied Energy, Vol. 11 pp. 197-213.

Geothermal power Frick, S., Kaltschmitt, M., Schroder, G., (2010) Life cycle assessment of geothermal binary power plants using enhanced low-temperature reservoirs, Energy, Vol. 35 pp. 2281-2294.

Geothermal Energy Association, (2010) Geothermal basics- Power plant costs www.geo-energy.org/geo_basics_plant_cost.aspx (Accessed 09/10)

Huttrer, G.W., (2001) The status of world geothermal power generation 1995-2000, Geothermics, Geothermics Vol. 30 pp. 1-27

Kaplan, S., (2008) Power Plants: Characteristics and Costs, CRS Report for Congress, www.fas.org/sgp/crs/misc/RL34746.pdf (Accessed 09/10)

Lawrence, S., (2008) Geothermal Energy, Leeds School of Business, University of Colorado, www.scribd.com/doc/6565045/Geothermal-Energy (Accessed 09/10)

MIT (2006) The Future of Geothermal Energy, Geothermal Program, Idaho National Laboratory, http://geothermal.inel.gov/publications/future_of_geothermal_energy.pdf (Accessed 09/10)

Saner, D., Juraske, R., Kubert, M., Blum, P., Hellweg, S., Bayer, P., (2010) Is it only CO2 that matters? A life cycle perspective on shallow geothermal systems, Renewable and Sustainable Energy Reviews, Renewable and Sustainable Energy Reviews Vol. 14 pp. 1798–181

U.S. Department of Energy, (2005) Buried Treasure: The Environmental, Economic and Employment Benefits of Geothermal Energy. NREL, Energy Efficiency and Renewable Energy, www.nrel.gov/docs/fy05osti/35939.pdf (Accessed 08/10)

Usui, C., Aikawa, K., (1970) Engineering and Design Features of the Otake Geothermal Power Plant, Geothermics, O. N. Symposium on the Development and Utilization of Geothermal Resources, Pisa tt) Vol. 2, Part 2

Biomass power Asgard Biomass (2009) Biomass fuels, www.asgard-biomass.co.uk/biomass_boiler_fuels.php (Accessed 09/10)

Bauer, C., (2008) Life Cycle Assessment of Fossil and Biomass Power Generation Chains, Paul Scherrer Institut, http://gabe.web.psi.ch/pdfs/PSI_Report/PSI-Bericht%2008-05.pdf (Accessed 09/10)

Ellington, R.T., Meo, M., El-Sayed, D.A., (1993) The Net Greenhouse Warming Forcing of Methanol Produced from Biomass, University of Oklahoma, Biomass and Bioenergy Vol. 4, No. 6, pp. 40-18.

http://hydropower.inel.gov/hydrokinetic_wave/pdfs/day1/09_heavesurge_wave_devices.pdf�

http://hydropower.inel.gov/hydrokinetic_wave/pdfs/day1/09_heavesurge_wave_devices.pdf�

http://www.devondare.org/wavepower�

http://www.aquamarinepower.com/pub�

http://peakenergy.blogspot.com/2010/09/wave-power-potential-in-australia.html�

http://peakenergy.blogspot.com/2010/09/wave-power-potential-in-australia.html�

http://www.pelamiswave.com/�

http://www.wavedragon.net/�

http://www.geo-energy.org/geo_basics_plant_cost.aspx�

http://www.geo-energy.org/geo_basics_plant_cost.aspx�


http://www.scribd.com/doc/6565045/Geothermal-Energy�

http://www.scribd.com/doc/6565045/Geothermal-Energy�

http://geothermal.inel.gov/publications/future_of_geothermal_energy.pdf�

http://geothermal.inel.gov/publications/future_of_geothermal_energy.pdf�

http://www.nrel.gov/docs/fy05osti/35939.pdf�

http://www.asgard-biomass.co.uk/biomass_boiler_fuels.php�

http://www.asgard-biomass.co.uk/biomass_boiler_fuels.php�

http://gabe.web.psi.ch/pdfs/PSI_Report/PSI-Bericht%2008-05.pdf�

http://gabe.web.psi.ch/pdfs/PSI_Report/PSI-Bericht%2008-05.pdf�


HM Government (2010) 2050 Pathways Analysis, www.decc.gov.uk/assets/decc/What%20we%20do/A%20low%20carbon%20UK/2050/216-2050-pathways-analysis-report.pdf (Accessed 09/10)

Kim, S., Dale, B.E., (2008) Cumulative Energy and Global Warming Impact from the Production of Biomass for Biobased Products Research and Analysis http://arrahman29.files.wordpress.com/2008/02/lca-use.pdf (Accessed 09/10)

Mann, M.K., Spath, P.L., (1997) Life Cycle Assessment of a Biomass Gasification Combined-Cycle Power System, National Renewable Energy Laboratory, www.nrel.gov/docs/legosti/fy98/23076.pdf (Accessed 09/10)

Pollack, A., (Sept 4, 2010) His Corporate Strategy: The Scientific Method, The New York Times, www.nytimes.com/2010/09/05/business/05venter.html?_r=1&src=me&ref=general (Accessed 09/10)

World Bank (2010) Commodity Prices, http://siteresources.worldbank.org/INTDAILYPROSPECTS/Resources/Pnk_0910.pdf (Accessed 09/10)

http://www.decc.gov.uk/assets/decc/What%20we%20do/A%20low%20carbon%20UK/2050/216-2050-pathways-analysis-report.pdf�



http://arrahman29.files.wordpress.com/2008/02/lca-use.pdf�

http://arrahman29.files.wordpress.com/2008/02/lca-use.pdf�

http://www.nrel.gov/docs/legosti/fy98/23076.pdf�

http://www.nytimes.com/2010/09/05/business/05venter.html?_r=1&src=me&ref=general�

http://www.nytimes.com/2010/09/05/business/05venter.html?_r=1&src=me&ref=general�

http://siteresources.worldbank.org/INTDAILYPROSPECTS/Resources/Pnk_0910.pdf�

http://siteresources.worldbank.org/INTDAILYPROSPECTS/Resources/Pnk_0910.pdf�

NUCLEAR POWER

1 MFA, 26/02/2010

Materials for Nuclear Power Systems

M. F. Ashbya,b and Michael Smidman

a

a. Engineering Department, Cambridge University, UK

b. Granta Design, 300 Rustat House, 62 Clifton Rd, Cambridge, CB1 7EG UK

January 2010 – Version 1.1

Contents

1. Introduction and synopsis ............................................................................................................................................ 2

2. Reactor types................................................................................................................................................................. 3

3. The Materials for Nuclear Power Systems database ................................................................................................. 7

4. Nuclear properties in the Elements database ........................................................................................................... 10

5. Summary and conclusions.......................................................................................................................................... 13

Appendix 1: Definition of nuclear properties............................................................................................................... 14

Appendix 2: Materials in nuclear power systems, listed by subsystem...................................................................... 15

Further reading............................................................................................................................................................... 19

Sizewell B atomic power station

2

1. Introduction and synopsis

Electricity generation, at present largely from fossil

fuels, accounts for 33% of the carbon entering the

atmosphere annually; transport accounts for another

28%. Fossil fuels are non-renewable and their use

releases carbon into the atmosphere with consequences

that are causing concern. Renewable energy sources

(wind, wave, tidal, solar, hydro, geothermal) can,

realistically, provide only a fraction of the energy we

use today, and a smaller fraction of the much larger

demand for energy that is predicted for 20 years from

now. All have a very small power-to-land-area ratio.

An option that is receiving increasing attention is to

replace carbon-based fuels by nuclear power (using it

for transport via electric or hydrogen-powered vehicles)

at the same time reducing an uncomfortable dependence

on imported hydrocarbons and an unacceptably

extensive use of land area.

Currently there are some 436 operational nuclear

reactors world-wide. They are predominantly

pressurized water reactors, PWRs, (60% of total) and

boiling water reactors, BWRs (21%). The rest are gas-

cooled reactors, AGRs, deuterium-moderated reactors,

CANDU and D2O-PWRs, light water graphite

moderated reactors, RBMKs, and fast breeder reactors,

FBRs.

There has been a virtual moratorium on building nuclear

power plants for the last 20 years. One consequence has

been the loss of expertise required to construct and

maintain them. The renewed interest in nuclear power

creates a need for engineers with appropriate training.

With hundreds of new reactors planned worldwide, such

training will be required on a significant scale.

Universities are seeking to respond by developing and

expanding courses on Nuclear Engineering.

A second consequence of the moratorium is the paucity

of texts for teaching about materials in nuclear reactors

– most date from 1980 or before. There are, however,

good web sites. Two, particularly, provide current

information about the field. They are listed in Further

Reading, at the end of this White Paper under

International Nuclear Safety Center (2009) and

European Nuclear Society (2009).

This White Paper describes a resource designed to

support introductory and higher level courses on nuclear

power systems, focusing on the choice of materials. It

centers on a pair of databases for materials of fission

and fusion-based Nuclear Engineering – fuels, materials

for fuel cladding, moderators and control rods, first-wall

materials, materials for pressure vessels and heat-

exchangers, providing data for their properties. Where

relevant the records contain data for both nuclear and

engineering properties. The databases are accessed

through the CES EduPack software, allowing its full

data-retrieval and selection functionality to be exploited.

The following sections describe and illustrate the use of

the two databases. The content is summarized below

• Reactor systems are introduced in Section 2,

each with a figure identifying the principal

structural and functional materials. Records for

the reactor systems are linked to records for the

engineering properties of the materials in them

in a new database called “Nuclear power

systems”. Its structure, content, and uses are

described in Section 3.

• Fundamental nuclear properties of the elements

are stored in an expanded version of the

“Elements” database, the subject of Section 4.

Charts for nuclear properties, created with this

database, illustrate how it is used to select

materials with nuclear properties that best meet

the needs for moderators, control rods and fuel

cladding.

• Two Appendices list definitions of nuclear

properties and tabulate the materials used in

each reactor system.

Examples of the current number of operational reactors and projections for new build.

Country Operating reactors,

2009

Estimates of needed

new reactors

Source of

information

US 86 Not known

Russia 35 Not known

Europe: France 59 Not known

Europe: Germany 12 Not known

Europe: UK 10 15 The Times, 4 Oct 2009

Japan 60 Not known

China 11 300 The Times, Sept 2009

India 18 450 The Times, Sept 2009

3

2. Reactor types

A number of reactor types have been developed for

commercial service. The British Magnox reactors and

the Canadian Candu reactors are now reaching the end

of their lives. Most current commercial reactors are

based on boiling water (BWR) or pressurized water

(PWR) heat-transfer systems. Interest now focuses on

Generation IV designs: fast breeder, gas-cooled and

high-temperature reactors. Early versions of some, like

the Liquid-metal Cooled Fast Breeder Reactor

(LMFBR) and the Advanced Gas Cooled Reactor

(AGR), already exist. Others, such as the Pebble Bed

Reactor (PBR) are under study. Research on Fusion

Reactors has been underway for 30 years, but a

commercial system is still far away. One example, the

ITER reactor, is described here.

Reactor systems and the principle materials of which

they are made are introduced in this section.

2.1 Boiling Water Reactor (BWR)

See Figure 1. Coolant: light water; outlet temperature

560 K.

The direct cycle BWR system generates steam that is

fed to the same sort of steam turbine used in coal or gas-

fired power systems. The nuclear core assembly consists

of an array of Zircaloy 2 tubes encasing enriched UO2

ceramic fuel pellets. Some of the fuel rods contain

gadolinium oxide (Gd2O3), which acts as a burnable

“poison” absorbing neutrons when the fuel is fresh but

burning up as the fuel decays, buffering the neutron

flux. The power is controlled by control rods inserted

from the bottom of the core and by adjusting the rate of

flow of water. The control rods are made of boron

carbide (B4C) clad in stainless steel 304 or 304L. Water

is circulated through the reactor core where it boils,

producing saturated steam.

The water acts as both a coolant and a moderator,

slowing down high energy neutrons. The steam is dried

and passed to the turbine-generator through a stainless

steel steam line. On exiting the turbine the steam is

condensed, demineralized, and returned as water to the

reactor. The schematic in Figure 1 shows the most

important materials of the system.

The BWR operates at constant steam pressure (7 MPa),

like conventional steam boilers and with a steam

temperature of about 560K.

2.2 Pressurize Water Reactor (PWR)

See Figure 2 (overleaf). Coolant: light water; outlet

temperature 600 K.

The core of a pressurized water reactor (PWR) is not

unlike that of a BWR. It has some 200 tube assemblies

containing ceramic pellets consisting of either enriched

uranium dioxide (UO2) or a mixture of both uranium

and plutonium oxides known as MOX (mixed oxide

fuel). These are encased in Zircaloy 4 cladding. Either

B4C-Al2O3 pellets or borosilicate glass rods are used as

burnable poisons. Water, pumped through the core at a

pressure sufficient to prevent boiling, acts as both a

coolant and a moderator, slowing down high energy

neutrons. The water, at about 600 K, passes to an

intermediate heat exchanger. The power is controlled by

the insertion of control rods from the top of the core and

by dissolving boric acid into the reactor water. As the

reactivity of the fuel decreases, the concentration of

dissolved boron ions is reduced by passing the water

through an ion-exchanger. Control rods made of boron

carbide (B4C) or an Ag-In-Cd alloy are clad in Inconel

627 or stainless steel (304) tubes.

Figure 1. The Boiling Water Reactor

4

The primary pressurized water loop of a PWR carries

heat from the reactor core to a steam generator. The

loop is under a working pressure of about 15 MPa -

sufficient to allow the water in it to be heated to near

600 K without boiling. The heat is transferred to a

secondary loop generating steam at 560 K and about 7

MPa, which generates heat that drives the turbine.

2.3 Liquid Metal Fast Breeder Reactor (LMFBR)

See Figure 3. Coolant: sodium; outlet temperature

800K.

A LMFBR is a liquid sodium cooled reactor that makes

use of a fast neutron spectrum and a closed fuel cycle.

The liquid sodium coolant transfers heat from the

reactor core and is pumped through the primary loop at

about 800K. This sodium in this loop becomes

radioactive, requiring an intermediate sodium filled

heat-exchange loop to prevent possible leakage of

radioactive material outside the containment structure.

The sodium in this secondary sodium loop, made of

type 324 and 316 stainless steel, alloy 800 or Cr-Mo

steels, passes to a steam generator where it heats water

to generate steam at 750 K. The turbine and generator

are essentially the same as those of a BWR or PWR.

A variety of fuel materials have been proposed. These

include mixed uranium and plutonium oxides (~25%

PuO2), metal alloys such as U-Pu-Zr, and mixed

uranium or thorium carbides and nitrides. The usual

choice is a fuel assembly made up of mixed uranium

dioxide (UO2) and plutonium dioxide (PuO2) fuel rods

clad in type 316 stainless steel. This is surrounded by

the "breeding blanket" containing depleted UO2 pellets.

The control rods, like those of a BWR, are boron

carbide (B4C) clad in type 316 stainless steel and enter

from the top of the core.

An LMFBR can have either pool or loop designs. A

pool design has the intermediate heat exchangers and

primary sodium pumps immersed in the reactor vessel

whilst a loop design has these elements external to it.

The schematic shows a loop design. One of the selected

generation IV systems, the sodium-cooled fast reactor

(SFR) utilizes a similar design to the LMFBR described

above. The next generation lead-cooled fast reactor

(LFR) uses liquid lead as a coolant and utilizes a

somewhat different reactor design.

Figure 2. The Pressurized Water Reactor

Figure 3. The Liquid Metal Cooled Fast Breeder Reactor.

5

2.4 Advanced gas-cooled reactor (AGR)

See Figure 4 – typical power 660 MW. Coolant: CO2 ;

outlet temperature 943 K.

The advanced gas-cooled reactor (AGR) is graphite

moderated and cooled with carbon dioxide (CO2). The

core consists of high strength graphite bricks mounted

on a steel grid. Fuel rods of enriched UO2 clad in

stainless steel (20-Ni 25-Cr) are placed in graphite

sleeves and inserted into vertical channels in the bricks.

Gas circulators blow CO2 up through the core and down

into steam generators. Holes in the graphite allow

access to the gas. The outlet temperature of the CO2 is

about 943K at a pressure of 4MPa. The graphite in the

core is kept at temperatures below 723K to avoid

thermal damage.

The reactor core, gas circulators, and steam generators

are encased in a pressure vessel made of pre-stressed

concrete lined with a mild steel to make it gas tight.

Mild steel is used in areas of the pressure vessel that are

exposed to temperatures less than 623K. In regions at

temperatures between 623K and 793K, annealed 9Cr-

1Mo steel is used whilst austenitic steel (316 H) is used

for regions hotter than this. Power is primarily

controlled through the insertion of control rods made of

boron-steel, with back-up by insertion of nitrogen into

the cooling gas or by releasing fine boron-rich balls into

the gas stream.

2.5 Very High Temperature Reactors (VHTR).

E.g., the Pebble Bed Reactor (PBR). See Figure 5

(overleaf). Coolant: He; outlet temp. 1123–1223 K.

The very high temperature reactor (VHTR) is a

proposed IV generation design, moderated with graphite

and cooled with helium gas. The development of new

materials able to tolerate the higher operating

temperatures presents a major engineering challenge.

The outlet temperature of the coolant is about 1123-

1223K at a pressure of 7MPa. Internal reactor

temperatures may reach up to 1470K. Candidate

materials for regions at temperatures between about

1030K and 1270K are alloys 617, X, XR, 230, 602CA

or variants of alloy 800H. For regions with higher

temperatures than this, the leading material candidates

are composites with a carbon fiber reinforced carbon

matrix (Cf/C) or carbon fiber reinforced silicon carbide

(SiCf/SiC). The most promising pressure vessel material

is modified 9 Cr-1 Mo steel. Some designs maintain the

vessel at lower temperatures, in which case current

pressure vessel materials could be used such as SA 508

steels.

The helium coolant is heated in the reactor vessel and

flows to the intermediate heat exchanger (IHX). Heat is

transferred to a secondary loop with either helium,

nitrogen and helium, molten salt, or pressurized water.

The materials of the IHX depend on the operating

temperatures and the nature of the secondary coolant;

Alloy 617 is a primary candidate. The heated fluids can

either be used to drive a turbine or to produce hydrogen.

All VHTR designs make use of tri-structural isotropic

(TRISO) coated fuel particles. The particles are 750-830

µm in diameter and consist of a kernel of fuel material

coated with two layers of pyrolytic carbon with a layer

of silicon carbide in between. These particles can be

utilized in either prismatic or pebble bed reactors. In a

prismatic reactor the kernel consists of enriched

uranium oxycarbide (UCO) and the particles are packed

into cylindrical compacts which are placed into graphite

fuel elements. However a pebble bed reactor uses

particles with an enriched uranium dioxide (UO2) kernel

and these are formed into 60 mm diameter spheres (the

“pebbles”). The fuel pebbles are fed into the core mixed

with non-fuel graphite pebbles that act as reflectors to

even the heat generation.

Figure 4. The Advanced Gas-cooled Reactor (AGR).

6

2.6 Fusion Reactors: the International Thermonuclear Experimental Reactor (ITER)

See Figure 6.

The International Thermonuclear Experimental Reactor

(ITER) is an experimental fusion reactor designed to

produce 500MW of power from an input of 50MW. It is

a step towards the use of the fusion energy for

electricity production and other commercial

applications.

In all proposed fusion reactors, energy is released from

the fusion of deuterium and tritium nuclei. This requires

a temperature of about 100MK at which the gases forms

a plasma. No materials operate at such temperatures, so

the ITER uses magnetic confinement to contain

the plasma, allowing fusion without contact

between the plasma and the containing walls.

The ITER uses a tokamak design. The plasma

is contained in a torus shape using strong

magnetic fields produced by circumferential

superconducting coils and a large central

solenoid. The coils are made of a

superconducting niobium-tin alloy (Nb3Sn) or

niobium-titanium (NbTi) alloy cooled to 4K

with supercritical helium.

The plasma is enclosed in a sealed torus

vacuum vessel made up of two steel walls with

water coolant circulating between them. The

main structural materials are 316L(N)-IG,304

and 660 stainless steels. The inside of the

vacuum vessel is covered with the blanket that

shields the vessel and magnets from heat and

neutron radiation. This consists of shield

modules attached to the vacuum vessel inner

wall. Each module has a 316L(N)-IG stainless

steel shield block carrying a first wall panel of

beryllium facing the plasma. These are joined

to a heat sink made of a copper alloy (CuCrZr) with

316L(N)-IG stainless steel tubes with a coolant flowing

through them. It is the energy transferred to this coolant

that would be used in electricity production in future

plants.

At the bottom of the vacuum vessel is the diverter which

removes heat, helium ash and plasma impurities.

Materials of the diverter facing the plasma must

withstand temperatures of up to 3300K. The current

choice of materials are a carbon fibre composite (CFC

SEP NB31) and tungsten (99.94wt% W).

The entire structure, including the magnets, is enclosed

in a stainless steel vacuum cryostat.

Figure 5. A pebble bed advanced nuclear reactor. In some designs the helium heat-transfer

medium drives turbines to compress the gas and generate power; in others it is fed to a heat

exchanger where it passes its heat to a secondary helium loop or to steam loop, as pictured here.

Figure 6. The International Thermonuclear

Experimental Reactor (ITER)

7

3. The Materials for Nuclear Power Systems database

The database has three linked data-tables (Figure 7).

The first contains records for the power systems

themselves, each with an image indicating the principle

structural materials as described in Section 2. Each

reactor-system record is linked to records for the

materials of which it is made, contained in the second

data table, basically that of CES EduPack’s Level 3,

enlarged to contain records for fuels, control-rod

materials and special reactor-grade steels and graphites ,

listed below.

• Graphite (isotropic, HTR grade IG-110 )

• Graphite (semi-isotropic AGR Gilsoncarbon)

• Uranium dioxide (UO2)

• Uranium carbide (UC)

• Mixed oxide (U,Pu)O2 (MOX) 20% PuO2

• Uranium nitride

• Zirconium-1.5%tin alloy, reactor grade,

"Zircaloy 4"

• 9Cr-1Mo steel

• Modified 9Cr-1Mo-V steel (Grade 91)

• SA-508 Gr.3 Cl 1 and 2

• SA-533 Gr B

Records in both these data-tables are linked to listings

of relevant data sources stored in the third table.

The records for the principal structural materials include

the temperature dependence of Young’s modulus, yield

strength, ultimate strength and thermal conductivity,

stored as functions. This allows the dependence to be

plotted as in Figures 8 and 9, and the property values to

be displayed for a given operating temperature.

Figure 7. The data structure of the Nuclear

Power Systems database.

Figure 8. The thermal conductivity, Young's modulus, ultimate tensile strength and yield strength

of 304L stainless steel

8

The values of the thermal conductivity of the irradiated

graphite are considerably lower than the room

temperature value for the material (129-133 W/m.K).

This emphasizes that the change in properties under

neutron irradiation can be considerable and therefore the

inclusion of the properties of irradiated materials where

possible is important.

Using the database

The features of the database are best illustrated by

examples.

Example 1. Browsing and searching the Reactor

Systems data-table. The records for the reactor

systems, identified by both long and short name (e.g.

Pressurized water reactor, PWR) can be found by

browsing the record list, or by a text-search for the

name. Each record contains a descriptive image and text

that are essentially identical with those in subsections of

Section 2 of this White Paper. They can be copied and

pasted into Word.

Example 2. Browsing and searching the Materials

data-table. The CES EduPack software allows the user

to explore nuclear power systems by Browsing through

the hierarchically structured Materials tree, or by

Searching by name. The record on the next page shows

the result of a search on Zircaloy 2.

Example 3. Listing the principal materials of a given

reactor system. The Tree Selection tool in CES

EduPack allows names of all the records linked to a

given reactor system to be listed. The table shows the

result of tree selection for materials for pressurized

water reactors. Clicking on any member of the list opens

the record.

Materials in PWRs

Alumina, pressed and sintered Stainless steel, austenitic, AISI

304, wrought, annealed

Boron carbide (hot pressed) Stainless steel, austenitic, AISI 308, wrought, annealed

Borosilicate - 2405 Stainless steel, austenitic, AISI 308L, wrought, annealed

Carbon steel, AISI 1020, normalized

Stainless steel, austenitic, AISI 316, wrought, annealed

Mixed oxide (U,Pu)O2 (MOX) 20% PuO2

Stainless steel, austenitic, AISI 347, wrought

Nickel-Cr-Co-Mo alloy, INCONEL

617, wrought

Stainless steel, ferritic, AISI


Nickel-Fe-Cr alloy, INCOLOY

800, annealed

Thoria, ThO2

Nickel-chromium alloy, INCONEL 600, wrought, annealed

Titanium, alpha-beta alloy Th-6Al-4V

SA-508 Gr.3 Cl 1 and 2 Uranium dioxide , UO2

SA-533 Gr B Zirconium-tin alloy, Zircaloy-4, 1.5%Sn (reactor grade)

Example 4. Materials and reactor sub-systems. One

material listed above is AISI 347 austenitic stainless

steel. In which subsystem is this used? Opening the

record for AISI 347 and scrolling to Reactor Subsystem

reveals the answer – the primary cooling system.

Example 5. Materials proposed for use in fusion

reactors. A tree stage to isolate materials linked to the

ITER fusion reactor design results in the list below.

Materials proposed for use in fusion reactors

Beryllium, grade 0-50, hot isostatically pressed

Beryllium, grade I-250, hot isostatically pressed

Beryllium, grade S-200FH, hot isostatically pressed

Carbon fiber reinforced carbon matrix composite (Vf:40%)

Carbon fiber reinforced carbon

matrix composite (Vf:50%)

Epoxy SMC (glass fiber)

Epoxy/E-glass fiber, woven fabric

composite, qI laminate

Nickel iron aluminum bronze,

(wrought) (UNS C63020)

Hi conductivity Cu-Cr-Zr (wp) (UNS C18100)

Nickel-chromium alloy, INCONEL 718, wrought

Nickel iron aluminum bronze, (wrought) (UNS C63020)

OFHC copper, 1/2 hard (wrought) (UNS C10200)

Nickel-chromium alloy, INCONEL 718

Silver, commercial purity, fine, cold worked, hard

PTFE (unfilled) Stainless steel, austenitic, AISI 304, wrought, annealed

Stainless steel, austenitic,

316L(N)-IG

Stainless steel, austenitic, AISI


Stainless steel, austenitic, AISI 304L, wrought

Nitronic 50, XM-19, wrought, (nitrogen strengthened)

Stainless steel, austenitic, AISI 316L, wrought

Stainless steel, ferritic, AISI 430, wrought, annealed

Stainless steel, ferritic, AISI 430F, wrought, annealed

Stainless steel, ferritic, AISI 430FR, wrought, annealed

Titanium, alpha-beta alloy, Ti-6Al-4V, annealed, generic

Tungsten, commercial purity, R07004, annealed

Figure 9. The temperature dependence of the thermal

conductivity of irradiated AGR graphite

9

Zircaloy-2 (reactor grade) Designation ASTM Standard B350-80: Zirconium-Tin Alloy, UNS R60802

Tradenames ZIRCALOY 2; SANDVIK ZIRCALOY 2, Sandvik Steel Co. (USA); ZIRCALOY-2, Sandvik/Coromant (USA); ZIRCALOY-2, Westinghouse Electric Corp. (USA);

Composition (summary) Zr/1.2-1.7Sn/.07-.2Fe/.05-.15Cr/.03-.08Ni/+ various lesser impurities

Composition detail Base Zr (Zirconium) Cr (chromium) 0.05 - 0.15 % Fe (iron) 0.07 - 0.2 % Ni (nickel) 0.03 - 0.08 % Sn (tin) 1.2 - 1.7 % Zr (zirconium) 97.9 - 98.7 %

Density 6450 - 6650 kg/m3

Price * 24.7 - 27.2 USD/kg

Mechanical properties Young's modulus * 90 - 105 GPa Shear modulus * 30 - 40 GPa Bulk modulus * 100 - 150 GPa Poisson's ratio * 0.35 - 0.38 Yield strength (elastic limit) 240 - 490 MPa Tensile strength 410 - 520 MPa Compressive strength * 240 - 490 MPa Flexural strength (modulus of rupture) * 240 - 490 MPa Elongation 14 - 32 % Hardness - Vickers 200 - 240 HV Fatigue strength at 10

7 cycles * 160 - 260 MPa

Fracture toughness * 115 - 150 MPa.m1/2

Mechanical loss coefficient (tan delta) * 3e-4 - 9e-4

Thermal properties Melting point 2100 - 2130 K Maximum service temperature * 643 - 783 K Thermal conductivity 11 - 14 W/m.K Specific heat capacity 274 - 286 J/kg.K Thermal expansion coefficient 5.5 - 5.9 µstrain/°C

Typical uses Fuel rod cladding in boiling water reactors (BWR).

Warning May become radioactively contaminated during use. Small pieces of zirconium, e.g. machine chips and turnings, can be a fire hazard. Non-radioactive Zirconium is toxic, but only if ingested in large quantities.

Other notes The mechanical properties of Zr alloys vary strongly with oxygen impurity levels. Zirconium ore naturally contains a few per cent Hafnium, which has v. similar properties to Zr. For nuclear applications, this has to be removed, as Hf absorbs neutrons.

Figure 10. The record for the cladding material Zircaloy 2. Nuclear properties for zirconium (the

base of Zircaloy) are contained in the extended Elements database, described in Section 4.

10

Example 6. Using the links between material and

reactor system. Which reactor systems use Graphite

Grade IG-110 as a moderator? Opening the record for

this Graphite (found by Browsing or by Searching) and

activating the link to Reactor Systems gives the result

shown below.

Nuclear power systems

Very high temperature reactor (VHTR)

Example 7. Using the links between material and

reactor system. Which reactor system can use uranium

carbide as a fuel? Opening the record for Uranium

Carbide (found by Browsing or by Searching) and

activating the link to Reactor Systems gives the result

shown below.

Liquid metal fast breeder reactors

Example 8. Listing properties at temperature. What

is the thermal conductivity and the yield strength of

wrought 316L stainless steel at 350ºC? Entering 350ºC

(or 623 K) as the temperature parameter value for the T-

dependent properties of 316L (found by Browsing or by

Searching) gives

Thermal conductivity 19 W/m/C

Yield strength 104 MPa

4. Nuclear properties in the Elements database

The existing Elements database has been expanded to

include relevant nuclear properties for reactor

engineering: the binding energy per nucleon, thermal

neutron absorption cross section, thermal neutron

scattering cross section, and, for fuels, the half life.

These properties are defined more fully in Appendix 1.

Additional records have been added for particular

isotopes of interest: deuterium (2), tritium (3), the four

isotopes of plutonium (239, 240, 241, 242), the three

isotopes of uranium (233, 235, 238), the two of thorium

(232, 233) and one each of protactinium (233),

samarium (149), xenon (135) and boron (10).

Data for the binding energy per nucleon data were

largely drawn from the tabulation of Audi et al (2003,a).

Binding energy per nucleon is isotope-specific, so

unless the isotope was specified, the value for the most

abundant isotope was used. The half lives of isotopes,

from Audi et al (2003,b) are listed only for records that

are isotope-specific. Values of the absorption and

scattering cross-sections are from Glasstone and

Sesonske (1994), which also contained the cross

sections of some isotopes not found elsewhere. The

remaining cross sections for the isotopes are from the

compilation of nuclear data of the IAEA (2008).

CES EduPack allows the data to be presented in ways

that bring out features of interest – Figures 11 to 14.

Figure 11. The binding energy per nucleon, a measure of nuclear stability, for the elements of the

periodic table. The most stable nucleus is that of iron, though many others lie close.

11

Figure 12. The neutron capture cross-section for scattering and for absorption for the elements

of the periodic table. Diagonal contours show the ratio of the two.

Figure 13. The combination of scattering cross sections and atomic weight that characterizes

the effectiveness of an element as a neutron moderator. Hydrogen, oxygen (water) and

graphite are all effective moderators.

12

The first is a plot of binding energy per nucleon against

atomic number. The most stable nuclei (those with the

greatest binding energy) cluster around iron. It is clear

from this plot that elements with a higher atomic

number than iron will generally favor fission whilst

those lower than iron will generally favor fusion, and

that fission releases, at most, a few hundred keV per

event, whereas fusion can release many thousands.

Moderator materials. Figure 12 shows the scattering

cross-section sσ against the absorption cross-section

aσ . Neutron moderators slow neutrons by elastic

collisions that ultimately reduce their energy from keV

to a few kT (about 0.1 eV) by elastic collisions, without

absorbing them (absorption results in transmutation and

unwanted fission products). Thus good moderator

materials have high sσ and low aσ . They are the

materials at the upper left of Figure 12. The

effectiveness of a moderator also depends on the mass

of the nucleus, since this determines the momentum

transfer in a collision with a neutron. A more

meaningful measure of effectiveness as a moderator

takes this into account. It is the moderating ratio M:

M = ξσs/σa,

where ξ is the fraction of neutron energy lost per

scattering event and is given by

ξ = 6/(3A+1)

where A is the atomic mass number. Figure 13 is a plot

of the moderating ration against atomic number. A high

ratio indicates a good moderating behavior. The most

used moderators are light water H2O, heavy water, D2O,

carbon (graphite) and beryllium, exactly as the figure

suggests.

Control-rod materials. Control rods absorb neutrons,

controlling the rate of fission of the fuel by quenching

the chain reaction that generates them. The best

materials for such control have high absorption cross-

sections, but do not themselves transmute to fissionable

material. These are the material on the extreme right of

Figure 12, excluding the fuels uranium, plutonium and

thorium. Thus control rods are generally made of

cadmium, indium, silver, boron, cobalt, hafnium,

europium, samariium or dysprosium, often in the form

of alloys such as Ag-In-Cd or compounds such as boron

carbide, hafnium diboride or dysprosium titanate. The

absorption capture cross-sections of these elements

depends on neutron energy so the compositions of the

control rods is chosen for the neutron spectrum of the

reactor that it controls. Light water reactors (BWR,

PWR) operate with thermal neutrons, fast reactors with

high-energy “fast” neutrons.

Cladding materials. Nuclear fuel rods are made up of

fuel pellets contained in tubular cladding, which

separates the fuel from the coolant. Cladding materials

must be corrosion resistant, they must conduct heat

Figure 14. Materials for cladding: adequate melting point, resist corrosion in the cooling

medium and have minimal cross-section for absorption.

13

well, and have low absorption cross-section so that

neutrons pass through them easily; and of course they

must have a melting point well above the operating

temperature of the fuel rods. Figure 14 shows

absorption cross-section and melting temperature of

potential cladding materials. Those most commonly

used are based on zirconium or beryllium (bottom row

of elements) or on stainless steel, the ingredients of

which (iron, nickel, chromium) appear in the second

row up. Advanced reactors, now under consideration,

may require cladding with a higher melting point.

5. Summary and conclusions

As outlined above, the CES EduPack software provides

a useful means of exploring nuclear power systems and

the materials associated with them. The ability to find

out about reactor systems and immediately access

details of the associated materials is something offered

by the data structure of the Nuclear Power Systems

database. The fact that it is possible to view the

materials in the context of the reactor system and then

access the relevant properties is of educational benefit

and allows a greater understanding of materials

selection for nuclear power systems. The inclusion of

temperature dependent properties of materials and the

effect of neutron irradiation represents some of the most

important factors in materials selection for reactor

design. This is an example of how the existing CES

EduPack database has been adapted in the most

appropriate manner for the topic as well as considering

what is useful in an educational context. The absence of

functional data for some materials is mainly a result of

the lack of publicly available data. The fact that the CES

EduPack selection tools can also be applied to

temperature dependent data shows benefits of accessing

it through the software.

The modifications to the Elements database bring out

the influence of fundamental physics on material

selection considerations. As shown in the previous

section, the production of a small number of graphs

using the CES EduPack software are able to largely

justify the materials selected for reactor systems as well

as demonstrating fundamental principles behind the

fission process. Energy dependent cross section data for

certain isotopes has been included. These have been

selected on the basis of educational considerations.

However the Elements database is not a comprehensive

database of neutron reactions. The CES EduPack

software is not designed to accommodate the volume of

data associated with such a database and access to

comprehensive reaction data is readily accessible

through the internet. Therefore the focus of the CES

EduPack database has been to be selective about the

data stored such that it is useful in bringing out the

issues discussed above.

Overall, it is now possible to view nuclear power

systems at different levels through the CES EduPack

system. From largest scale of reactor systems to

smallest scale of nuclear properties it is possible to gain

an understanding of materials selection issues of nuclear

reactor systems. With the inclusion of details on certain

next generation reactors including a prototype fusion

reactor the software allows the exploration of material

considerations of future technologies. This is during a

time in which the process of materials selection for next

generation technologies is still underway. An

understanding of the relevant considerations at all levels

is therefore vital.

14

Appendix 1: Definition of nuclear properties

Binding energy per nucleon (Usual units: keV)1

The binding energy B is the energy required to break

apart a nucleus into its constituent nucleons. The

difference between the mass of the isolated nucleons

and the mass of a bound nucleus is the mass defect ∆m .

The total binding energy of the nucleus, B is given by

2c∆m=B

where c is the speed of light in a vacuum. The binding

energy per nucleon is A/B where A is the number of

nucleons in the nucleus. It varies between isotopes so

that some are more stable than others. The value listed

in the database is that for the most abundant isotope

unless otherwise stated.

Half life (Usual units: years)

The time after which the number of a given radioactive

nuclides in a sample halve by radioactive decay. If there

are oN radioactive nuclides at a time 0=t , the number

of radioactive nuclides N at a time t is given by

tλexpN=N o −

where λ is the decay rate. The half life 2/1t is the time

at which 2/N=N o , giving

( )λ

2ln=t 2/1

Cross sections (Usual units: barns)2

The cross section for a process is the measure of a

probability of the process occurring. For a neutron

induced process it is the effective area presented by a

target nuclei to a beam of neutrons, and thus has the

dimensions of area. For a thin sheet of nuclei with

number density n and an incident neutron beam of

fluxΦ , the rate of the process occurring per unit volume R is given by

σnΦ=R

1 1 keV = 1.6 x 10-16 Joule = 3.38 x 10-17 calories.

2 1 barn = 10-24 cm2 = 10-28 m2

σ is the cross section (also called the microscopic cross

section).

• Absorption cross section, aσ . The

microscopic cross section for the absorption of

a neutron by an atom. This is the sum of the

fission and capture cross sections.

• Scattering cross section, sσ . The microscopic

cross section for the scattering of a neutron by

an atom.

• Fission cross section, fσ . The microscopic

cross section for the absorption of a neutron by

an atom and the subsequent splitting of the

target atom.

Different isotopes have different values of σ. Unless

otherwise stated the value is given for a natural mixture

of isotopes. The value of σ is strongly dependent on

neutron energy; the values in the database are for

thermal neutrons of energy 0.025eV.

15

Appendix 2: Materials in nuclear power systems, listed by subsystem

Materials in fission reactors

PWR*

Fuel and

cladding

Coolant /

Moderator

Control Pressure vessel Piping/Internals IHX/Steam

generator

Enriched

UO2/MOX

Zircaloy 4

Light Water Ag-In-Cd

B4C

304 SS

Inconel 627

Boric Acid

Borosilicate glass

Al2O3

SA508 Gr.3 Class

1,2

SA533 Gr.B

308SS, Inconel

617 (Clad)

304SS

316SS

ASTM 516 Gr.70

308L

SA533 Gr.B

Inconel 600

Incoloy 800

SA515 Gr.60

* Andrews and Jelley (2007); Glasstone and Sesonske (1994); Roberts (1981)

BWR*

Fuel and

cladding

Coolant /

Moderator


generator

Enriched UO2

Gd2O3

Zircaloy 2

Light Water B4C

304 SS

SA508 Gr.3 Class

1,2

SA533 Gr.B

308L SS (Clad)

304 SS

316, 316L

304L

347Inconel

SA106 Gr.B

SA333 Gr.6

SA533 Gr.B

Inconel 600

Incoloy 800

SA515 Gr.60

* Andrews and Jelley (2007); Glasstone and Sesonske (1994); Roberts (1981)

AGR*

Fuel and

cladding

Coolant /

Moderator


generator

Enriched UO2

25Cr-20Ni SS

Graphite*

CO2

Graphite

Boron Steel

Cd

Nitrogen

Boronated glass

Pre-stressed

concrete

Mild steel

Mild Steel

Annealed 9Cr-

1Mo steel

18Cr-12Ni SS

Mild Steel

Annealed 9Cr-

1Mo steel

18Cr-12Ni SS

*Frost B.R.T. (1994); Nuclear_Graphite_Course; Marshall W. (1983)

16

LMFBR*

Fuel and

cladding

Coolant /

Moderator


generator

MOX

U-Pu-Zr

MC

MN

316 SS

Depleted UO2

Liquid Sodium B4C

316SS

Eu2O3

EuB6

304SS

316SS

316-FR

304SS

316SS

316-FR

Alloy 718

21/4 Cr 1 Mo Steel

(SA336)

9Cr-1Mo steels

(Modified)

Incoloy 800

304SS

316SS

* Andrews and Jelley (2007); Roberts (1981) ; Generation IV Nuclear Energy Systems (2007) Appendix 5.0

VHTR*

Fuel and

cladding

Coolant /

Moderator


generator

UCO

UO2

Pyrolytic Carbon*

Silicon carbide*

Helium

Graphite

Nitrogen

Molten Salt

Cf/C,SiCf/SiC

(Clad)

Modifield 9Cr-

1Mo-V Steel P91

SA508 Gr.3 Class

1,2

SA533 Gr.B

Alloys 617

X, XR, 230,

602CA, 800H

Carbon fibre

reinforced carbon

Cf / C

SiCf / SiC

Alloy 617

Alloy 230

*Petti et al (2009); Riou et al (2004); Natesan et al (2006); Generation IV Nuclear Energy Systems (2007) Appendix 1.0

Materials in fusion reactors: ITER*

Material Forms

Thermal shield

Stainless steel AISI 304L Plates, tubes

Ti-6Al-4V Plates

Steel grade 660 Fasteners

INCONEL 718 Bolts

Al2O3 coatings Plasma sprayed insulation

Glass epoxy G10 Insulation

Ag coating Coating, 5µm (emissivity)

17

Vacuum vessel and ports

Stainless steel 316L(N)-IG Plates, forgings, pipes

Stainless steel AISI 304 Plates

Steel 660 Fasteners, forgings

Ferritic stainless steel 430 Plates

Borated steels 304B7 and 304B4 Plates

INCONEL 718 Bolts

Stainless steel 316L (B8M) Bolts

Austenitic steel XM-19 (B8R) Bolts

Pure Cu Clad

VV support

Stainless steel AISI 304 Plates, rods

Steel 660 Fasteners

INCONEL 718 Bolts

NiAl bronze Rods

PTFE Plates

First wall

Beryllium (S-65C or equivalent) Armor tiles

CuCrZr Plates/cast/powder heat sink

Stainless steel 316L(N)-IG Plates, pipes

Blanket and support

316L(N)-IG Plates, forgings, pipes Cast, powder HIP

Ti-6Al-4V Flexible support

CuCrZr Sheets

INCONEL 718 Bolts

NiAl bronze Plates

Al2O3 coatings Plasma sprayed insulation

CuNiBe or DS Cu Collar

18

Diverter

Cf / C (NB31 or equivalent) Armor tiles

Tungsten Armor tiles

CuCrZr Tubes, plates

Stainless steel 316L(N)-IG Plates, forgings, tubes

Steel 660 Plates, bolts

Austenitic steel XM-19 Plates, forgings

INCONEL 718 Plates

NiAl bronze Plates, rods

*Barabash et al, (2007); Ioki K. et al (1998); Nishi, H. et al (2008); Tokamak aspx

19

Further reading

Andrews, J. and Jelley N. (2007) “Energy science”,

Oxford University Press, Oxford, UK. ISBN 978-0-19-

928112-1

Angell, M.G, Lister, S.K, Rudge, A (2008) “The effect

of steam pressure on the oxidation behaviour of

annealed 9-Cr1-Mo boiler tubing materials” (Preprint).

Available at http://www.icpws15.de/papers/06_Electro-

10_angell.pdf as of 02/09/2009

Audi G. et al (2003,b) "The Nubase 2003 evaluation of

nuclear and decay properties" Nuclear Physics A, vol.

729, page 3-18.

Audi,G., Wapstra, A.H. and Thibault, C. (2003,a)

"Ame2003 atomic mass evaluation (II)" Nuclear

Physics A729 p. 337-676.

Barabash,V. and the ITER International Team, Peacock,

A., Fabritsiev, S., Kalinin, G., Zinkle, S., Rowcliffe, A.,

Rensman, J-W., Tavassoli, A.A., Marmy, P. Karditsas,

P.J., Gillemot, F. and Akiba, M. (2007) “Materials

challenges for ITER”, J. Nuclear Materials, 367-370,

pp.21 – 32.

Brookhaven National Laboratories (2009)

http://www.nndc.bnl.gov/exfor/endf00.jsp as of

02/09/2009

European Nuclear Society (2009) www.euronuclear.org

Foster, A.R. and Wright, R.L. Jnr. (1977) “Basic

nuclear engineering”, 3rd edition, Allyn and Bacon Inc.

Boston, MA, USA. ISBN 0-205-05697-0.

Frost B.R.T. (1994) “Nuclear Materials” vols 10A and

10B, in “Materials Science & Technology” (VCH series

eds R.W. Cahn, P. Haasen, E.J. Kramer) VCH,

Weinheim, Germany.

Frost, B.R.D. and Waldron, M.B. (1959) “Nuclear

reactor materials”, Temple Press, London, UK.

Generation IV Nuclear Energy Systems Ten-Year

Program Plan - Fiscal Year 2007 Appendix 5.0

available at

https://inlportal.inl.gov/portal/server.pt?open=514&objI

D=2604&mode=2

Generation IV Nuclear Energy Systems Ten-Year

Program Plan - Fiscal Year 2007 Appendix 1.0

Glasstone, S. and Sesonske, A. (1994) “ Nuclear reactor

engineering” 4th edition, Chapman and Hall, New York,

NY, USA. ISBN 0-412-98521-7.

Greenfield, P. (1972) “Zirconium in nuclear

technology” Mills & Boon Monographs, London. ISBN

0-263-05112-9

http://www.iter.org/mach/Pages/Tokamak.aspx

Official website of the ITER as of 02/09/2009

IAEA Handbook of nuclear data for safeguards:

Database extensions, August 2008. Available at

http://www-nds.iaea.org/sgnucdat/safeg2008.pdf as of

08/07/2009.

International Nuclear Safety Center, (2009), Argonne

National Laboratories http://www.insc.anl.gov/matprop/

(A property database for materials used in nuclear

reactors. Useful, but at present incomplete.)

Ioki K. et al (1998) “Design and material selection for

ITER first wall/blanket, divertor and vacuum vessel”

Journal of Nuclear Materials 258-263 74-84

Kopelman, B. (1959) “Materials for nuclear reactors”,

McGraw Hill, Reading, Mass.

Lamarsh, J.R. (1975) “Introduction to nuclear

engineering” Addison Wesley, Reading, MA, USA.

ISBN 0-201-04160-X.

Ma, B.M. (1983) “Nuclear reactor materials and

applications” Van Nostrand Reinhold, NY, NY. ISBN

0-442-22559-8

Marshall W. (1983) “Nuclear power technology”

Clarendon press, Oxford, UK ISBN 0-19-851948-6

Mcintosh, A.B. and Heal, T.J. (1960) “Materials for

nuclear engineers”, Temple Press, London.

Natesan, K. et al (2006) “Preliminary Issues Associated

with the Next Generation Nuclear Plant Intermediate

Heat Exchanger Design”

Natesan, K. et al (2006) “Preliminary Materials

Selection Issues for the Next Generation Nuclear Plant

Reactor Pressure Vessel” all available at

https://inlportal.inl.gov/portal/server.pt?open=514&objI

D=2604&mode=2 as of 02/09/2009

Nishi, H. et al “Study on Characteristics of Dissimilar

Material Joints for ITER First Wall” (Preprint) available

at http://www.fec2008.ch/preprints/it_p7-11.pdf as of

02/09/2009

Nuclear_Graphite_Course available at

http://web.up.ac.za/sitefiles/file/44/2063/Nuclear_Graph

ite_Course/B%20-%20Graphite%20Core%20Design

%20AGR%20and%20Others.pdf as of 02/09/2009

Nuttall W.J. (Editor) (2005) “Nuclear Renaissance”,

Taylor & Francis, London UK

20

Petti, D. Crawford, D. Chauvin, N. (2009) “Fuels for

advanced nuclear energy systems” MRS Bulletin vol 34.

Riou B. et al (2004) “Issues in Reactor Pressure Vessel

materials” 2nd International Topical Meeting on high

temperature reactor technology.

Roberts, J.T.A. (1981) “Structural materials in nuclear

power systems” Plenum Press, New York, NY, USA.

ISBN 0-306-40669-1.

Smith, C.O. (1967) “Nuclear reactor materials”,

Addison Wesley, Reading, Mass, USA, Library of

Congress Number 67-23981.

Ursu, I. (1985) “Physics and technology of nuclear

materials”, Pergamon Press, Oxford. ISBN 8-08-

032601-3.

Was, G. S. (2007) “Fundamentals of radiation materials

science: metals and alloys” Springer Verlag, ISBN: 978-

3-540-49471-3

Materials for Energy Storage Systems

Materials for Energy Storage Systems © Granta Design, Jan 2012

Mater ia ls for Energy Storage Systems—A Whi te Paper

Mike F Ashby and James Polyblank Engineering Department, University of Cambridge, Trumpington Street, Cambridge, CB2 1PZ, UK

Version 2.0, first published January 2012 © Granta Design, 2012

Image of flywheel for regenerative braking, courtesy of BP Research Centre, Sunbury, UK.

Materials for Energy Storage Systems © Granta Design, Jan 2012

Table of Contents

1. Introduction—the need for energy storage systems ................................................................1

2. Overview—selecting energy storage systems .........................................................................2

3. Pumped hydro storage ...........................................................................................................11

4. Compressed air energy storage (CAES) ...............................................................................12

5. Springs ...................................................................................................................................14

6. Flywheels ...............................................................................................................................16

7. Thermal Storage ....................................................................................................................17

8. Batteries .................................................................................................................................18

9. Hydrogen Energy Storage .....................................................................................................23

10. Capacitors and super-capacitors .........................................................................................24

11. Superconducting Magnetic Energy Storage (SMES) ...........................................................26

Appendix 1 Definition of terms ...................................................................................................27

Appendix 2: Approximate Material Intensities for Energy Storage Systems ..............................29

Further Reading .........................................................................................................................34

Materials for Energy Storage Systems 1 © Granta Design, Jan 2012

1. Introduction—the need for energy storage systems

Energy storage systems are the source of power for products as diverse as hearing aids and satellites. Two sectors have a particular interest in large-scale energy storage systems: the utilities industry and the automotive industry. The portable electronics industry and the military also require energy storage systems, but on a smaller scale.

The utility industry is faced with the problem that energy demand is not constant but fluctuates through the day. With the increasing dependence on renewable energy sources (wind, wave, solar), energy supply, too, fluctuates. Energy storage systems ensure that, when supply is high and demand is low, energy is not wasted, and that when supply is low and demand is high, the demand can still be met. An electricity grid allows electricity to be generated at one

location and used at another. Energy storage systems allow electricity to be generated at one time and used at another. The automotive industry has rather different needs. Legislation to reduce emissions is driving the development of a new generation of low carbon vehicles. Gasoline is an exceptionally effective form of portable energy. Replacing it requires a storage system that can provide acceptable range and allow acceptably fast refueling or recharging.

This report surveys prominent energy storage systems (Table 1). Section 2 provides an overview of the findings and describes how energy storage systems can be selected. Subsequent sections provide a deeper analysis of each system, with a particular emphasis on their ultimate limits and the demands they place on material supply.

Table 1. Classes and members of energy storage systems.

Class Systems Hydrocarbons (for comparison) Conventional fuels

Mechanical storage Pumped hydro

Compressed air energy storage

Springs

Flywheels

Thermal storage Thermal storage

Chemical storage Li-ion batteries

Sodium-sulfur batteries

Lead-acid batteries

Nickel cadmium batteries

Nickel-metal hydride batteries

Vanadium flow batteries

Hydrogen fuel cells

Electro-magnetic storage Super capacitors

Superconducting magnetic energy storage


As we found with systems for low carbon power generation (see Materials for Low-Carbon Power—A White Paper), the performance of energy storage systems depends on the type and scale of the system, its location, and the way it is managed. Technical developments continue to improve the performance of existing systems and add new ones. The figures and tables of this paper show representative ranges, but there is no guarantee that these ranges enclose all members of a given system.

2. Overview—selecting energy storage systems

Even within the utility industry and the automotive industry, there are different applications of energy storage devices. The utility industry needs short bursts of energy at high power for frequency regulation (that is, maintaining a constant mains frequency), while they need more sustained power for energy management (ensuring that demand is met, and supply is not wasted). Similarly, the automotive industry needs short bursts of energy for acceleration and more sustained power for

long distance cruising.

Six performance metrics for energy storage systems appear in Table 2. Specific energy and energy density are the energy storage capacity per unit mass and unit volume respectively. The operating cost is the approximate cost of one charge/discharge cycle of one unit of energy, and includes the cost of maintenance, heating, labor, etc. Specific power is the discharge power capacity per unit mass. The efficiency is defined as the ratio of total energy outputted by the system over total energy put into the system in one charge/discharge cycle. The cycle life is defined as the number of charge/discharge cycles possible until the capacity of the storage system drops to 80% of its initial capacity.

Figure 1 identifies the storage systems which are best for short power bursts and those able to provide more sustained power. The axes are Specific power (power per unit mass) and Specific energy (energy storage capacity per unit mass), with contours of constant discharge time. Superconducting magnetic energy storage (SMES), electric double layer capacitors

Figure 1. A plot of power density against energy density of energy storage systems, with lines of charge/discharge time.


(EDLC, also known as super-capacitors or ultra-capacitors), and flywheels can provide short bursts of power, while pumped hydro storage and thermal storage are better suited for longer duration power supply.

Once a selection of storage systems with suitable discharge times have been identified for a given application, it then remains to select the energy storage system which has the best performance, and the lowest resource intensities.

Table 2. Performance metrics of energy storage systems1

Storage System

.

Specific Energy

Energy Density

Operating Cost

Specific Power

Efficiency Cycle Life

(MJ/kg) (MJ/m3) ($/MJ) (W/kg) (%) (#-cycles)

Conventional fuels 20-50 15,000-72,000

- - 18-50 1

Pumped hydro 0.002-0.005 2-5 0.0006-0.0014

0.02-0.3 70-80 400,000

Compressed air energy storage

0.36 25 0.0001-0.0019

8 65-70 15,000

Springs 0.00014-0.00033

0.6-1.1 - - 98-99.9 Depends on loading2

Flywheels

0.002-0.025 2.1 0.0008-0.0017

100-10,000

75-85 150,000

Thermal storage 0.032-0.036 160 0.0008-0.0019

1.5-1.7 72-85 10,000-15,000

Li-ion batteries 0.32-0.68 720-1,400 0.0019-0.0047

250-340 80-90 300-2,000

Sodium-sulfur batteries 0.2-0.7 140-540 0.0039 10-15 75-83 3600-4700

Lead-acid batteries 0.07-0.18 200-430 0.0008-0.0028

4-180 70-90 200-1500

Nickel cadmium batteries

0.08-0.23 72-310 0.0008-0.0055

30-150 60-85 800-1200

Nickel-metal hydride batteries

0.1-0.43 190-1300 0.0006-0.0028

4-140 65-85 300-1000

Vanadium flow batteries 0.07-0.13 110-170 0.0039 2.2-3.1 71-88 10000-16000

Hydrogen fuel cells 0.02-0.8 1-70 0.0006-0.0041

5-20 27-35 5,000-10,000

Super capacitors 0.010-0.020 10-25 0.0008-0.0019

1,000-20,000

90-95 1,000,000

Superconducting magnetic energy storage

0.001-0.02 2-10 0.0003-0.0083

500-20,000

85-92 50,000-200,000

1 Some of the data in this table are easy to find, but others are not. Some have to be estimated from diagrams or schematics of the system, some deduced by analogy with similar systems, and some inferred from the physics on which the system depends. The values vary greatly with design, location and scale of the system, allowing wide variation. That means precision is low, but the difference between the values of competing systems is sufficiently great that it is still possible to draw meaningful conclusions. 2 The cycle life of a spring depends on loading—for low alloy steels, for example, an increase in loading of 50% can reduce the lifetime by six orders of magnitude.


The importance of each performance metric depends on the application. The automotive industry requires energy storage systems that are small and light, so are interested in high Specific energy and Energy density. These two metrics are the axes of Figure 2. Compared to fuels, with specific energies from 20 MJ/kg (for methanol) to 50 MJ/kg (for LPG) and energy densities from 16,000 MJ/m3 (for methanol) and 72,000 MJ/m3 (for coal), all of the “low carbon” energy storage systems perform poorly. Their specific energies and energy densities are at least one order of magnitude smaller than those of hydrocarbon fuels. Even explosives (which must include both reactants, whereas the masses of fuels do not include the oxygen the fuel reacts with) store much more energy than any other storage system per unit mass or volume.

Many of these systems are not yet fully mature; future research and development will certainly improve their performance. But there are upper limits, physical and practical, beyond which performance

cannot be pushed. A plot of these upper limits for specific energy and energy density (Figure 3) shows how they might compete with fuels in the future. The assumptions used to estimate these values are discussed in later sections. They are extremely optimistic. The ratio of the current specific energy to the estimated upper limit of each system (Figure 4) is around 1% for all except CAES and SMES, suggesting that there is some consistency in the level of optimism that has been applied. With the most optimistic assumptions, the only energy storage systems that approach the energy densities of fuels are hypothetical flywheels made from carbon nano-tubes (CNTs), hypothetical lithium-fluorine batteries, and superconducting magnetic energy storage (SMES). Even approaching these limits is improbable because of practicalities discussed in the subsequent sections of the report. It is very hard to compete successfully with hydrocarbon fuels.

Figure 2. Specific energy and energy density of energy storage methods, including a number of fuels for comparison. The densities of most solids sit within an order of magnitude of that of water (1,000kg/m3), so it is

no surprise that physical density of all the storage systems (apart from gases) sit within this range.


Figure 4. The ratio of the current specific energy to the limiting specific energy of energy storage systems.

Figure 3. A plot of energy mass density vs. energy volume density optimistically achievable by various technologies.


Figure 5 and Figure 6 show bar-charts of cycle efficiency and cycle life. Poor efficiency means large losses, making storage expensive. Poor cycle life makes

investment in the system less attractive because of the cost and inconvenience of replacement.

Figure 5. Cycle efficiency of energy storage systems. Fossil fuel engines/power plants are included for comparison.

Figure 6. Cycle life of energy storage systems.


Constructing an energy storage system requires resources. Five resource intensities of construction appear in Table 3. All are quoted per unit of energy-storage capacity. Capital intensity is the cost of construction per MJ of storage capacity. Area intensity is the typical area used to site the storage system, per MJ of

storage capacity. Material intensity is the mass of raw materials required to construct the storage system, per MJ. Energy intensity is the primary energy required to construct the storage system, and CO2 intensity is the CO2 emitted in constructing the storage system, per MJ of storage capacity.

Table 3. Resource intensities of construction of energy storage devices3

Storage System

.

Capital Intensity

Area Intensity Material Intensity

Energy Intensity

CO2 Intensity

($/MJ) (m2/MJ) (kg/MJ) (MJembodied/MJ) (kg-CO2/MJ)

Conventional Fuels

0.045-0.0654 - - 0.1-0.24 0.2-0.44

Pumped Hydro 45-120 0.02-0.08 60-120 100-200 8-16

Compressed Air Energy Storage

4-20 0.008 2-12 74 5.3

Springs 500-1,600 - 3,000-7,100 340,000-550,000

24,000-42,000

Flywheels 400-7,000 0.08-0.2 17-500 750-760 90-100

Thermal Storage 14-26 0.003 0.4-50 120-130 8.9-9.0

Li-ion Batteries 140-440 0.002-0.008 1.5-2.7 330-580 19-50

Sodium-Sulphur Batteries

28-280 0.005-0.008 1.4-5 360-640 30-50

Lead-Acid Batteries

50-220 0.009-0.03 4.5-12 110-980 5-130

Nickel Cadmium Batteries

200-330 0.006-0.03 3.5-10 390-640 28-47

Nickel-Metal Hydride Batteries

130-440 0.003-0.03 2-7 550-940 28-67

Vanadium Flow Batteries

100-300 0.01 3.8-7 170-180 25-26

Hydrogen Fuel Cells

55-2,300 0.001-0.015 1.3-50 140-150 9.7-9.8

Super-capacitors 14,700-41,000 0.11-0.13 45-65 3,700-6,500 210-360

Superconducting Magnetic Storage

30,000-260,000 0.25-7.1 50-1,000 1,600-1,700 240-250

3 Some of the data in this table are easy to find, but others are not. Some have to be estimated from diagrams or schematics of the system, some deduced by analogy with similar systems, and some inferred from the physics on which the system depends. The values vary greatly with design, location, and scale of the system, allowing wide variation. That means precision is low, but the difference between the values of competing systems is sufficiently great that it is still possible to draw meaningful conclusions. 4 Note that conventional fuels can only be used once, so these figures cannot be compared directly with the other systems, but are included for completeness.


The capital and energy required to install a given energy-storage capacity depends on capital and energy intensities of the storage system. Figure 7 illustrates this. It has axes of

lifeCyclecapactiystorageofMJperenergyonConstructi

and

lifeCyclecapactiystorageofMJpercapitalonConstructi

Compressed air energy storage has the lowest capital intensity per MJ-cycle. Super-capacitors are the least energy intensive storage system, largely because of their high cycle life. The energy and capital intensities of batteries are inflated by their lower cycle life, making some of them more expensive and more energy intensive per cycle than gasoline.

Investment decisions for energy storage are influenced by the total cost per unit storage capacity per cycle. This is:

Figure 8 plots this for each system. It reveals that CAES is still the cheapest.

Large scale implementations of energy storage systems for grid stability makes considerable demands on material supply and land area, making Material intensity and Area intensity metrics of particular importance to the utility industry. They are plotted in Figure 9. Thermal storage, lithium-ion batteries, and hydrogen storage use the least area and materials.

) / ($ cost ) / ($ cost ) / ($ cost

cycle MJ Operating life Cycle

MJ Construction cycle MJ Average

− + =

−

Figure 7. The capital and energy intensities of construction of energy storage systems, both per cycle over the lifetime of the system.


Using an overall material intensity is, of course, an oversimplification. What is important is which materials are used, and whether they are “critical”. The bills of materials for the energy storage systems studied here are listed in Appendix 2.

These allow a comparison between the demands of each system and the current world production of critical materials, highlighting where supply might be a problem.

Figure 8. Total costs of energy storage systems per unit storage capacity per cycle.

Figure 9. The area and material intensities of energy storage systems.


What is a critical material? There are four reasons for a material to be categorized in this way:

• Production is primarily from sources considered unreliable for geo-political reasons;

• Lack of substitutes for the material in its main application;

• Supply is limited due to the economics of its production; or

• Extreme price volatility.

The annual productions of 27 materials that meet one or more of these criteria are shown in Figure 10, color-coded to show the reasons for concern.

In subsequent sections we examine each energy storage system in turn, paying particular attention to critical materials. To do this we consider a hypothetical scenario, one that is compatible with that used in Materials for Low-Carbon Power—A White Paper. To complement the 2,000 GW of power generation capacity hypothetically being replaced over a 10 year period, 10 hours of storage capacity will be installed. This will require a storage capacity of 20,000 GWh, or 72 PJ (petajoule = 1015J). From this we calculate the fraction of current world production of each critical material that would be required to build the installations, revealing where material supply might be a problem.

Figure 10. Current (2010) annual world production of 27 critical materials, highlighting the reasons for their being identified as critical.


3. Pumped hydro storage

Energy is stored if water is pumped from a lower reservoir to an upper reservoir that is 100-1,000 m higher (Figure 11). Energy is recovered by allowing the water to return to the lower reservoir through a generator like that of a hydro-power plant.

The gravitational potential energy stored in a mass of water by pumping it to a height is:

(1)

where is the acceleration due to gravity (10 m/s2). Assuming that the mass and volume of the dam and ancillary equipment are negligible compared to those of the water and that energy is recovered with 100% efficiency, the specific energy and the energy density are

and (2)

where is the volume of water and is the density of water (1,000 kg/m3). The quantities and are approximately constant on earth, so the specific energy

and energy density of a pumped hydro system depend only on —the height of the upper reservoir above the lower one. To put an absolute upper limit on this, we postulate a pumped hydro system with the upper reservoir at the highest point on earth (Everest at 8,850m), and the lower reservoir at sea level, giving the (unattainable) limits

and

mh

hgmW =

g

hgmW

= hghgVm

VW ρ==

V ρ

ρ g

h

kgMJkgJxmW /09.0/885010

*==

3

3 *

/ 90

/ 000 , 500 , 88 8850 10 1000

m MJ

m J x x V W

=

= =

Figure 11. Diagram of a pumped hydro storage system.


Even this fantasy scenario gives values of specific energy and energy density that are almost three orders of magnitude smaller than those of oil. Real systems have values that are between 10 and 100 times smaller still.

The simplicity of pumped hydro systems makes them the preferred method of utility-scale energy storage, accounting for 99% of world-wide capacity. An approximate bill of materials for such a system appears in Appendix 2. It suggests that the material demands for large scale deployment (following the scenario described in Section 2) would be manageable, requiring only 0.2% of the world production of chromium and manganese, the only critical materials required. The greatest obstacle to expansion is simply that of finding useable locations.

4. Compressed air energy storage (CAES)

CAES systems store energy by compressing air. Energy is recovered by expanding the air through a pneumatic motor or turbine connected to a generator. The compressed air can be stored in small tanks for mobile (e.g., automotive) applications, or in underground caverns or large balloons under the sea (which keeps it at high pressure) for utility scale applications.

When air is compressed its temperature rises. If this heat leaks away, energy is lost. When the air is expanded again, it cools and can freeze the turbine. There are two ways of dealing with this. One is to insulate the compressed air chamber so that the heat does not escape, allowing adiabatic compression. The other is to pump slowly and allow the heat to escape or to be stored separately so that the temperature of the compressed air chamber remains constant, giving isothermal compression. Isothermal

Figure 12. Diagram of a hybrid CAES system.


compression must be followed by slow, isothermal expansion, allowing the heat to return to the air. In theory, either method could be 100% efficient, but in practice an efficiency of about 70% is the best achievable.

Today’s CAES systems combine compressed air with natural gas. The gas burns to heat the air before the mixture enters the turbine (Figure 12). In a conventional gas power plant, substantial energy is used to compress air. The stored compressed air removes the need for this, increasing the efficiency. Taking out the contribution of the gas, CAES systems have an efficiency of 70% for round-trip compressed air storage.

Large scale deployment of CAES systems would be manageable, requiring only using 0.001% of the annual production of chromium, and 0.3% of manganese (Appendix 2). Mobile applications require a pressure vessel, but this is unlikely to put pressure on supply of critical materials.

The specific energy of today’s CAES systems is about 0.36 MJ/kg, and the energy density is about 25 MJ/m3 , barely 1% of the values for hydrocarbon fuels. Could they be improved? The energy stored by isentropically compressing n moles of air at temperature T from pressure pA to pB into a pressure vessel of volume is:

(3)

The mass of a thin walled spherical vessel of radius, r, thickness, t, and made out of material of density, ρ, is:

(4)

The wall thickness required to ensure that the wall does not yield under a pressure difference is:

(5)

where is the yield strength of the wall

material. Substituting this into equation (5) gives:

(6)

The volume of the pressure vessel is

, allowing this equation to be re-

expressed as:

(7)

To minimize the mass, we need to maximize . The structural material

with the largest value of this index is CRFP with MJ/kg. Noting that,

at high pressures the mass of the vessel is:

(8)

where pressures are in units of MPa and volume in m3. The mass of the air itself (at 300K):

(9)

where is the density of air at atmospheric pressure (1.2 kg/m3 at 0.1 MPa). The specific energy is thus:

(10)

It only remains to select the compression pressure. The most powerful compressors available today typically compress from atmospheric pressure (0.1 MPa) to 100 MPa. (These compressors are used for hot isostatic pressing for powder

V

=

=−

A

BB

A

BBA p

pVp

pp

TnRW lnln

ρπ trm 24=

p∆

y

rpt

σ∆

≥21

yσ

y

3 pr2m

σ∆ρπ

=

334 rV π=

y

pVm

σρ

23 ∆

=

ρσ /y

6.1/ =ρσ y

Bpp ≈∆

Bvessel pVm 94.0=

Vp12Vpp

m BA

Bairair == ρ

airρ

) MJ/kg p p

ln( 08 . 0

V p 12 V p 94 . 0

) p p

ln( V p

m m W

A B

B B A B

B

air vessel

=

+ =

+


processing of materials.) This gives a specific energy of 0.55 MJ/kg, and an energy density of 580 MJ/m3. Even without the pressure vessel (e.g., in a solution mined salt cavern), the specific energy would be 0.59 MJ/kg. This is still two orders of magnitude smaller than conventional fuels.

It should also be noted that, in calculating this upper limit, we have applied no safety factor (it should be at least 3), neglected the low efficiency of pneumatic pumps (20 – 30%), and assumed 100% energy recovery (in reality 80% at best). It is clear that compressed air storage can work for utility power but for mobile applications it cannot compete with fossil fuels.

5. Springs

Springs store energy by compressing or extending material elastically. There are no examples of springs being used for utility scale energy storage or to provide propulsion in automobiles. This is because they have very low specific energy. We highlight this here by considering the maximum energy we could store in a spring using today’s materials.

The specific energy, energy density, and the capital intensity of energy storage in a

material when stretched uniaxially to yield are:

Energy density (11,a)

Specific energy (11,b)

Capital intensity (11,c)

where is energy stored, is the volume of material, is the mass of material, is the total cost of material,

is the yield stress of the material, is

the Young’s modulus, is the density, and is the material cost per unit mass. Table 4 lists values for five different materials.

Table 4. The performance of various materials for springs.

Material MJ/m3 MJ/kg USD/MJ Cycle Efficiency

Polyurethane rubber (Unfilled) 30-400 0.03-0.4 20-200 40-70%

PEBA (Shore D25) 21-38 0.021-0.038 220-400 70-94%

Epoxy/S-glass fiber (0° ply) 30-33 0.015-0.017 1500-1700 98%

Low alloy steel, AISI 9255, tempered 205°C

8-12 0.001-0.0015 550-830 99.8-99.9%

Carbon nano-tubes 8,400 5 30,000-160,000

EVW y

2

21 σ

=

EmW y

ρ

σ 2

21

=

22

y

mCEWC

σ

ρ=

W Vm

C

yσ E

ρ

mC

Figure 13. A titanium spring. Image courtesy of G and O Springs Ltd.


Polyurethane rubber is the best according to all three of these figures of merit. However cyclically compressing and expanding polyurethane rubber is extremely lossy, with a mechanical loss coefficient of tan(δ)=0.05-0.1, leading to a cycle efficiency of 40-70%. PEBA (Shore D25) has a better material efficiency of 94%, but has a lower specific energy of 0.021-0.038 MJ/kg compared to 0.03-0.4 MJ/kg for polyurethane rubber. Epoxy/S-glass fiber makes the lightest and smallest spring, while low alloy steel makes the cheapest. These have much higher cycle efficiencies (98% and 99.9% respectively), but the overall efficiency will be reduced by the mechanisms used to store and extract the energy. Thus the energy density of springs made from today’s materials is three orders of magnitude smaller than conventional fuels.

Hill et al. (2009) claim that it would be possible to store 8,400 MJ/m3 or 5 MJ/kg

in carbon nano-tube springs. This might be true of a single nanotube, but scaling up to any useful size requires that the nanotubes are bonded in some kind of matrix, reducing the specific energy. A more realistic upper bound is to postulate that the spring material could be loaded to the theoretical strength, roughly . Then using (as an example) the modulus and density of steel (200 GPa and 7,900 kg/m3) we find upper bounds from equations 11,a and 11,b as follows.

Energy density:

Specific energy:

These are still far below the values for hydrocarbons.

10/E

32y m/MJ1000

100E

21

E21

VW

===σ

.kg/MJ13.0100

E21

E21

mW

2y

ρρ

σ==

Figure 14. Diagram of a flywheel. The motor/generator is adapted to fit inside the flywheel to save space. The system is buried underground for safety.


6. Flywheels

A spinning flywheel stores kinetic energy (Figure 14), which is recovered by coupling the flywheel to a generator. An efficient flywheel is designed to have as large a rotational moment of inertia as possible and to spin fast. Frictional losses in the bearings and surrounding air reduce efficiency. They are reduced by using superconducting magnetic bearings to levitate the rotor and by cooling or pumping the air out of the containment. All of these require energy, so they too reduce efficiency slightly.

Present-day flywheels have a specific energy in the range 0.002 – 0.025 MJ/kg and an energy density is between 1.7 and 23 MJ/m3 when ancillary devices are included, values that are much smaller than hydrocarbon fuels. What are the upper limits for both? The following estimate gives an idea.

The kinetic energy of a rotating cylinder is:

(12)

where is the rotational moment of inertia and the angular velocity. The moment of inertia is maximized for a given mass of material by making it into a thin-walled tube. If the tube has mass , radius and wall thickness

(Figure 15, left), its moment of inertia per unit length is:

(13)

Equating the centrifugal load in a small element of this ring to the resolved component of the circumferential stress in the wall when this stress is just below the its yield strength gives the maximum

allowable angular velocity, :

from which

(14)

giving a specific energy of

MJ/kg (15)

where is in MPa and the density is

in kg/m3. Among today’s materials, CFRP has the highest value of

1.6 MJ/kg, allowing a flywheel with specific energy of 0.8 MJ/kg. This is two orders of magnitude smaller than the value for hydrocarbons, and we have not included the protective burst shield, the motor-generator, or any safety factors (up to five for composite materials)—all of which reduce the specific energy.

221 ωIW =

Iω

mR t

2RmI =

yσ

ω

ydtRdtRRdm σθωθρω == 22 )(

ρ

σω

22

Ry

=

ρ

σ y

21

mW

=

yσ ρ

≈ρσ /y

Figure 15. Left: A flywheel. The maximum kinetic energy it can store is limited by its strength. Right: Demand ratios for critical materials used in flywheel energy storage systems with superconducting

magnetic bearings. *CFRP is included because, even though it is not a critical material, large scale implementation is likely to stretch its supply.


It has been suggested that flywheels might be constructed that exploited the great strength ( = 100 GPa, Peng et al.,

2008) and low density ( = 1,300 kg/m3, Collins & Avouris, 2000) of carbon nano-tubes, allowing a specific energy of 40 MJ/kg, comparable with conventional fuels. However, this neglects the need for a supporting matrix. A more realistic upper limit, following the reasoning of the previous section, is to imagine a material with the density and modulus of steel and with the theoretical strength , giving a specific energy

MJ/kg

Large scale implementation of flywheel storage systems with superconducting bearings using yttrium barium copper oxide superconductors and CFRP disks (Appendix 2) could exert pressure on supply of yttrium and CFRP (Figure 15, right).

7. Thermal Storage

Thermal energy storage takes two forms.

1. Heating an inert solid or liquid, using its heat capacity (specific heat), (J/kg.K) to retain energy,

2. Causing a solid to melt, using its latent heat of fusion, (J/kg) to capture energy.

Energy is recovered by passing a heat-transfer fluid through the hot or molten body, passing the heat to a heat exchanger where it generates steam or hot gas for space heating or to drive a turbine. Utility-scale thermal energy storage is used to smooth the power output of concentrated solar plants (Figure 16). The sun’s radiation is focused on a collector containing molten salt (typically 40% potassium nitrate, 60% sodium nitrate). The molten salt is held in hot tanks until the energy is needed when an oil-loop from the hot tank carries the heat to a steam generator and turbine to generate electrical power.

yσ

ρ

.10/E

3.110

E21

21

mW y ===

ρρ

σ

pC

mL

Figure 16. Diagram of a molten salt thermal storage system connected to a solar tower. Only the thermal storage block is included when considering material usage.


The specific energies of present-day thermal storage systems lie in the range 0.032 – 0.036 MJ/kg, comparable with batteries but at three orders of magnitudes smaller than hydrocarbon fuel. What is the upper limit on their performance? To answer that we need the thermal properties of thermal storage materials. Table 5 lists some of these.

The element with the greatest specific heat capacity is lithium (3.6 kJ/kg/K). Lithium melts at 180°C, but can be stored in its liquid state, conceivably up to 1000°C. If we assume that the specific heat capacity of liquid lithium is the same as that of the solid and add its latent heat of fusion (~0.4 MJ/kg), the total energy density becomes ~3.5 MJ/kg.

Latent heat storage offers substantial specific energy, stored and recovered over a narrow temperature range. The melting point determines the output temperature, so must be chosen to match the application. The energy density is then determined by the latent heat of fusion (Table 5).

Thermal energy storage creates no alarming demands for critical materials. Meeting the scenario described earlier could require 0.6% of the world production of chromium and 5% of that of nickel.

8. Batteries

Batteries store chemical energy. There two classes of battery. Primary batteries can only be used once, after which they can be recycled, but not recharged. Secondary batteries can be recharged 100-10,000+ times before they fail. Here, we consider six types of secondary batteries which have shown promise in utility scale or automotive scale energy storage: lead-acid, lithium ion (Li-ion), sodium-sulfur (NaS), nickel-cadmium (Ni-Cd or NiCad), nickel-metal hydride (Ni-MH), and vanadium redox flow batteries (VRB). Appendix 2 contains bills of material for each.

A battery consists of two half cells, each containing a metal and a salt solution of that metal (e.g., metal sulfate). The half cell with the more reactive metal (metal A, in this example) is the anode. The metal is oxidized:

−+ +→ exAA x 22

Material Melting point (oC)

Specific heat (kJ/kgoC)

Energy density (MJ/m3 oC)

Latent heat of fusion (MJ/kg)

Aluminum 660 0.92 2.5 0.39

Cast Iron 1,200 0.54 3.9 0.27

Lead 324 0.13 1.5 0.034

Lithium 180 3.6 1.9 0.43

Sodium 100-760 1.3 0.95 0.11

Molten alt (50% KNO3; 40% NaNO2) 140-540 1.6 2.6 -

Fireclay 1450 1.0 2.1-2.6 Approx 0.8

Granite 1450 0.79 1.9 Approx 0.85

50% Ethylene Glycol; 50% Water 0 3.5 3.7 Approx 0.3

Water 0 4.2 4.2 0.34

Table 5. Properties of materials for thermal energy storage.


Figure 17. Left: diagram of the discharge of a lead-acid battery. Right: Demand ratios for antimony and lead used in lead acid batteries.

*These are not critical, but large scale implementation is expected to stretch their supply.

Figure 18. Left: Diagram of the discharging of a lithium-ion battery. Right: Demand ratios for critical materials used in lithium-ion batteries.

The half cell with the less reactive metal (metal B) is the cathode. The metal ions from the solution are reduced:

The metals from each half cell are connected to an external load through a circuit that transports the electrons from the anode to the cathode, providing electrical power. In order to maintain balance of charge, anions (negatively charged ions) are allowed to pass through

a porous disk from one solution to the other.

Lead acid batteries (Figure 17) have a lead anode and a lead dioxide cathode. On discharge, both of these become lead sulfate. At the anode:

At the cathode the reaction is:

BexB x →+ −+ 22

−+− ++→+ eHPbSOHSOPb 244

4 4 2 2 2 3 H2O PbSO e HSO H PbO + → + + + − − +


Figure 19. Left: Diagram of the discharge of a sodium-sulfur battery. Right: Demand ratios for critical materials used in sodium-sulfur batteries.

Lead-acid batteries do not use critical materials in significant quantities. However, large scale implementation will require an increase in the supply of both lead and antimony (Figure 17, right).

Li-ion batteries (Figure 18) have an anode of graphite intercalated with lithium and a cathode of lithium compounds. During discharge, lithium ions move from the graphite anode:

The Li+ ions diffuse through the separator and are taken up by the lithium compounds (typically, a lithium metal oxide compound, LiMO) at the cathode:

Large scale adoption of Li-ion for automotive propulsion or utility electricity storage may be constrained by the supply of lithium and graphite. Figure 18, right, shows that large scale implementation would result in lithium usage which is about eighty times today’s supply. The demand for graphite could exceed three times today’s supply production.

Sodium-sulfur batteries (Figure 19) have an anode of molten sodium and a cathode of molten sulfur. On discharge, the sodium is oxidized and the ions pass through an alumina electrolyte to reduce the sulfur and create sodium polysulfide. The overall reaction is:

Graphite is used to contain the molten sulfur and prevent it from corroding the current collectors and casing. Large scale implementation of NaS batteries may stretch the supply of graphite, as it will use 40% of the annual supply (Figure 19, right).

Ni-Cd batteries (Figure 20) have a cadmium-plated anode and a nickel oxide-hydroxide plated cathode. On discharge, the cadmium at the anode is oxidized:

The nickel oxide-hydroxide is reduced:

CexLixCLix 66 ++→ −+

LiMOexLixMOLi x →++ −+−1

4242 SNaSNa →+

−− +→+ eOHCdOHCd 2)(2 2

−− +→++ OHOHNieOHOHNiO 22 )(2)(


Figure 20. Left: Diagram of the discharge of a nickel-cadmium battery. Right: Demand ratios for critical materials used in nickel-cadmium batteries. *Cadmium is included because, even though it is not a critical

material, large scale implementation is likely to stretch its supply.

Figure 21. Left: Diagram of the discharge of a nickel-metal hydride battery. Right: Demand ratios for critical materials used in nickel-metal hydride batteries.

Large scale implementation of Ni-Cd batteries could be constrained by of supply of nickel, cobalt, and lithium (Figure 20, right). Although cadmium is not classified as a critical material, assuring its supply could be a problem.

Nickel-metal hydride batteries (Figure 21) resemble Ni-Cd batteries, but the anode is plated with a metal hydride rather than cadmium. On discharge, the metal hydride is oxidized:

The nickel is reduced, as in the Ni-Cd batteries:

−− ++→+ eOHMOHMH 22

−− +→++ OHOHNieOHOHNiO 22 )(2)(


Figure 22. Left: Diagram of the discharge of a vanadium redox flow battery. Right: Demand ratios for critical materials used in vanadium flow batteries. *Vanadium is included because, although it is not a critical

material, large scale implementation is likely to stretch its supply.

The anode, typically, is a hydride of lanthanum, neodymium, praseodymium, or cerium. Of these, cerium has the largest annual production, so we assume that the large scale implementations would use cerium hydride. This would result in a bottleneck of cerium and nickel supply (Figure 21, right). Even if the large scale implementation used a mixture of the available metals, such that only ¼ of the cerium was used, this would still result in the use of 200 times the current annual production—and this ratio would be larger for the other elements.

Vanadium redox batteries (Figure 22) differ from other batteries. The electrolytes are stored in tanks, and are pumped through the battery cell, where they are reduced or oxidized. The anode and cathode electrolytes are made up of a solution of vanadium in different oxidation states. The anode electrolyte is a solution of vanadium (II) ions, which are oxidized to vanadium (III) ions on discharge:

The cathode electrolyte is a solution of vanadium (V) oxide ions, which are reduced to vanadium (IV) oxide ions:

Large scale implementation of VRBs would use a significant fraction of today’s production of graphite (Figure 22, right) and would stretch the supply of vanadium, even though this is not a critical material.

The ultimate limits for batteries

To determine the maximum theoretical specific energy of batteries, we need to consider the standard electrode potential (SEP) of various half-cells. Consider, as an example, a lithium anode and a fluorine cathode (ignoring any practicalities of making this safe!), a combination with an exceptional high SEP differences. The oxidation of lithium

has a standard electrode potential of 3.04 V, and the reduction of fluorine

has a standard electrode potential of 2.87 V. The overall reaction

−++ +→ eVV 32

−+−++ +→++ OHVOeHVO 22

−+ +→ eLiLi

−− →+ FeF 222

LiFFLi 22 2 →+


gives a cell voltage of V=5.91 V. For one mole of reactants, having a mass of 51.9 g, the two moles of electrons exchanged, with charge C = 2 x 96,485 Coulombs, will deliver the energy:

corresponding to a specific energy of 22 MJ/kg, comparable with that of conventional fuels (20 – 50 MJ/kg). Safety concerns have held back the development of the lithium-fluorine cell. The closest technology is the lithium-carbon monofluoride (Li-CFx) cell, which has the combined reaction:

The carbon maintains the fluorine in a safe compound, but reduces the theoretical energy density to 7.9 MJ/kg, which we will take as an upper limit for battery technology. In practice real (Li-CFx) cells have only achieved energy densities in the range 0.94 – 2.8 MJ/kg, and they are not rechargeable.

9. Hydrogen Energy Storage

Energy can be stored by using it to generate hydrogen by electrolysis of water (Figure 23). Energy is recovered by passing the hydrogen to a fuel cell to generate electricity. Electrolysis breaks the water into positive H+ ions (or protons) and oxygen. At the anode:

At the cathode:

In the fuel cell hydrogen passes the anode, where it is oxidized to hydrogen ions (or protons) and electrons at the anode:

At the cathode, oxygen is reduced with the hydrogen to form water:

The electrolyte allows passage of hydrogen ions but not electrons. The electrons flow through an external circuit,

moleMJxCVW /14.1485,96291.5 ===

CxLiFxCFLix x +→+ )(

−+ ++→ eHOOH 442 22

222 HeH →+ −+

−+ +→ eHH 222

OHeHO 22 244 →++ −+

Figure 23. Diagram of hydrogen energy storage.


where they deliver energy to a load. Catalysts are required at the cathode and anode, platinum at the anode, and nickel at the cathode. Their use raises concerns over supply: large scale deployment might use ~25% of nickel supply and 400% of world production of platinum (Figure 24).

Figure 24. Demand ratios for critical materials used

in hydrogen storage systems.

The performance metrics of hydrogen storage presented in Table 2, and used in subsequent charts, are based on conceptual designs of a hydrogen storage system for which a number of assumptions have been made. The data is based on hydrogen generators and fuel cells (Hydrogenics, 2010). The mass of the hydrogen generator was not included in the onboard hydrogen storage. The specific energy and energy density of the stored hydrogen are based on the US Department of Energy 2010 targets for hydrogen storage of 5.4 MJ/kg and 3.2 MJ/m3 (US Department of Energy,

2011), which have been met by MOF-177 (a zinc compound that absorbs hydrogen as a hydride).

The US Department of Energy has also set ultimate targets for the specific energy and energy density of hydrogen storage: 9 MJ/kg and 8,300 MJ/m3. These can be taken as the practical limits on hydrogen energy storage, assuming that they will not be significantly affected by the mass of the fuel cell and hydrogen generator. These are barely competitive with conventional fuels, but many automotive companies are already investing heavily in research on hydrogen power vehicles.

10. Capacitors and super-capacitors

A capacitor stores energy as electrical charge. At its simplest it consists of two closely-spaced plates with a dielectric between them (Figure 25, left). Energy is used to move charge from one plate to the other, creating a potential difference between them. Energy is extracted by allowing the charge to return, passing through an external load. Capacitors can be charged and discharged very quickly giving high specific power, but their specific energy is small, about 0.0001 MJ/kg.

Figure 25. Left A capacitor. Right: A super-capacitor


The energy stored in a capacitor is

where is the capacitance and is the voltage. However, the electric field cannot exceed the breakdown field, , which limits the voltage to , where is the distance between plates. The capacitance of a capacitor is given by

where is the electric permittivity of the dielectric, is the relative permittivity, is the permittivity of free space, and is the area of the plates. Assembling these results gives the maximum energy that the capacitor can contain without breakdown:

and a maximum specific energy

where is the mass and is the density of the dielectric. The maximum

specific energy of a number of dielectrics, listed in Table 6, suggests that capacitors with a styrene-butadiene dielectric might double the performance to 0.0002 MJ/kg.

Super-capacitors offer greater performance. Super-capacitors store the charges at the interface between activated carbon and a liquid electrolyte (Figure 25, right), rather than between two plates. Because of the large surface to volume ratio of activated carbon, and the vanishingly thin distance over which the charge is stored, super-capacitors have greater capacitance and energy densities of 0.01-0.1 MJ/kg. The band-gap of dielectric materials limits the maximum energy density achievable in super-capacitors to about 2 MJ/kg (House, 2009), still an order of magnitude less than that of conventional fuels.

Super-capacitors do not use critical materials so that large scale implementation would not result in supply bottlenecks.

Table 6. Properties of dielectric materials5

Dielectric

.

Dielectric constant, rε

Breakdown field, dV (MV/m)

Density, ρ(kg/m3)

Specific energy (MJ/kg)

Syrene-Butadiene Block Copolymer

2.45-2.55 85-140 1,000 0.0001-0.0002

Cyclo Olefin Polymer 2.13-2.47 67-73 1,000 0.00005

Transparent Polyamide (nylon)

3.3-4.6 49-51 1,000 0.00004-0.00005

Vermiculite 6-8 8-14 64-160 0.00002-0.00007

Mica 5.4-8.7 40-79 2,600-3,200 0.00001-0.00007

Alumina (97.6) 9.0-9.5 41-45 3,700-3,800 0.00002

5 Data from CES EduPack

221 VCW =

C V

dV

dVV d= d

dAC /ε= or εεε =

rε

oε

A

2max 2

1dor VdAW εε=

ρεε

2max

21 d

orV

mW

=

m ρ


11. Superconducting Magnetic Energy Storage (SMES)

Superconducting magnetic energy storage (SMES) systems store energy as a magnetic field, set up by passing current through a superconducting coil. Because there is no resistance, the current and the field, once established, continues to flow without consuming further power. Energy is recovered by discharging the current through an external load.

Superconducting magnets require refrigeration and that does consume power, reducing efficiency, especially over large periods. High temperature superconductors (HTS) such as YBCO—yttrium barium copper oxide—which become superconducting at ~77K require less power for refrigeration than low temperature ~4K superconductors (LTS), but they still need some. For this reason, SMES tends to be used for short term storage (e.g., for frequency regulation).

The energy density stored in a magnetic field is:

where is the magnetic flux density and is the permittivity of free space. The

energy density is maximized by maximizing , which, for a type-II superconductor, cannot exceed the upper critical field of the magnet windings. The upper critical field of YBCO is 250 T at a temperature of zero Kelvin. If 250 T can be achieved, an energy density of 25,000 MJ/m3 can be achieved. Assuming a similar physical density to today’s SMES devices, this would result in a specific energy of 50 MJ/kg. This is competitive with fuels, but is only achieved at unrealistically low temperatures, and does not include the mass of the cryostat and ancillary devices.

Based on current HTS-SMES systems, large scale implementation would result in a bottleneck of supply of Yttrium, essential for the superconducting YBCO magnets (Figure 26).

o

BVW

µ

2

21

=

B

oµ

B

Figure 26. Demand ratios for critical materials used in superconducting magnetic energy

storage.


Appendix 1 Definition of terms

Resource intensities of construction

Capital intensity US$/MJ The capital intensity of an energy-storage system is the cost of building or purchasing the system per megajoule of storage capacity. As an example, a typical alkaline AA battery has a capacity of around 13.5x10-3 MJ and costs about a dollar. Its capital intensity is:

Capital intensity = Cost/Storage capacity = 1 / 0.0135 = 74 $/MJ

Area intensity m2

The area intensity of an energy storage system is the area of land that the system typically occupies per megajoule of storage capacity. As an example, the Ffestiniog pumped hydro power station has an area of 340,000 m² and can store 4.7 x 106 MJ. Its area intensity is:

/MJ

Area intensity = Area/Storage capacity = 340,000 / (4.7 x 106) = 0.07 m2

Material intensity kg/MJ

/MJ

The material intensity of an energy storage system is the mass of material that the system typically requires per megajoule of storage capacity. As an example, a particular Bosch car battery has a capacity of 4.36 MJ and a mass of 23.2 kg. Its mass intensity is calculated as

Material intensity = Mass of material/Storage capacity = 23.2 / 4.36 = 5.4 kg/MJ

The bill of materials for a given storage system allows the material intensity to be broken down by material. These material-specific intensities can then be compared to the annual world production of that material to flag up systems that, if deployed widely, might be constrained by material supply.

Energy intensity MJ/MJ The energy intensity of an energy storage system is the energy required to create the system per megajoule of storage capacity. This includes the energy needed to extract and process raw materials, fabricate components, and construct the final plant, with transport at different stages of the construction process taken into account. As an example, the energy needed to build a hypothetical molten salt thermal storage system with a capacity of 7.2x106 MJ was calculated at 9.2x108 MJ. Its energy intensity is:

Energy intensity = Construction energy/Storage capacity = 9.2 x 108 /(7.2 x 106

CO

) = 128 MJ/MJ

2

The CO2 intensity (or carbon intensity) of an energy storage system is the CO2 (equivalent) released to the atmosphere as a consequence of its construction the system per megajoule of storage capacity. As an example, a hypothetical thermal energy storage system has a capacity of 7.2x106 MJ and causes the emission of 6.4x107 kg of CO2. The carbon intensity is:

intensity kg/MJ

CO2 intensity = CO2 emission/Storage capacity = 6.4 x 107 / (7.2 x 106

Operational parameters

) = 8.9 kg/MJ

Specific energy MJ/kg The specific energy of an energy-storage system is the energy the system can store per unit of its mass. As and example, a silver oxide button cell has a mass of 0.7 g (7x10-4 kg) whilst storing 2.2x10-4 MJ. Its specific energy is

Specific energy = Energy stored/Mass = 2.2 x 10-4 / (7 x 10-4

Energy density MJ/m

) = 0.31 MJ/kg

The energy density of an energy-storage system is the energy the system can store per unit of volume. As an example, a lead-

3


acid battery measuring 120x80x80 mm can store 0.3 MJ. Its energy density is:

Energy density = Energy stored/Volume = 0.3 / (7.7 x 10-4) = 391 MJ/m

Specific power W/kg

3

The specific power is the rate at which energy can be drawn from the system per unit of its mass. As an example, the Maxwell VCAP350 super-capacitor weighs 63 g (6.3x10-2 kg) and can discharge with a continuous power of 67.5 W. Its specific power is calculated to be

Specific power = Energy per second/Mass = 67.5 / 0.063 = 1071 W/kg

Economic energy-storage capacity W/kg The economic energy storage capacity is the range of energy for which a particular storage system is economically viable. As an example, it is impractical to create a pumped hydro storage plant for a tiny amount of amounts of energy. It is equally impractical to use silver oxide batteries to store megajoules of energy.

Economic energy power capacity W/kg The economic power capacity of an energy storage technology is the range of power outputs that systems can deliver economically.

Cycle efficiency % The cycle efficiency is the percentage of the energy put into a system that is recovered when the energy is retrieved. This is measured for a typical cycle time, and will usually decrease if cycle is unusually long. As examples, a battery will slowly discharge if unused and frictional losses of a flywheel increase the longer it is spinning.

Cycle efficiency = (Energy output / Energy input) x 100

Cycle life - The cycle life is the number of times an energy storage system can charged and

discharged before the capacity of the system drops below 80% of its initial capacity. Cycle life is limited by factors such as fatigue in mechanical systems and electrolyte degradation in electrochemical systems.

Operating cost US$/MJ The operating cost is the approximate cost of one charge/discharge cycle of one unit of energy, and includes the cost of maintenance, heating, labor, etc.

Adaptable for mobile systems Yes/No Adaptable for mobile systems. If ticked (meaning Yes) the energy storage system is suitable for providing mobile power such as powering an automobile or a portable communication device.

Upper limits for performance metrics

Theoretical max specific energy MJ/kg The maximum specific energy of an energy storage system is the theoretical upper limit to the energy it can store per unit mass. As an example, the theoretical strength, roughly E/10 (where E is Young’s modulus) sets an absolute upper limit to the energy that could be stored in springs and flywheels.

Theoretical max energy density MJ/mThe maximum energy density of an energy storage system is the theoretical upper limit to the energy it can store per unit volume. As an example, the theoretical strength, roughly E/10 (where E is Young’s modulus) sets an absolute upper limit to the energy that could be stored in springs and flywheels.

3

Status

Current installed capacity GJ The current installed capacity is the sum of the energy storage capacities of all systems using a certain technology worldwide.

Growth rate % per year The growth rate is the rate of additional energy capacity added per year, expressed as a percentage of the current installed capacity.


Appendix 2: Approximate Material Intensities for Energy Storage Systems

Bills of materials for energy storage systems are assembled here. They are expressed as material intensities, , meaning mass (kg) of each material per unit (MJ) of energy storage capacity. There is no systematic, self consistent assembly of such data of which we are aware, so it has to be patched together from diverse sources. These differ in detail and scope. Some, for instance, are limited to the system alone, others include the copper and other materials needed to connect the system to the grid. Others give indirect information from which missing material content can be inferred. So be prepared for inconsistencies.

Despite these difficulties there is enough information here to draw conclusions about the demand that a commitment to any one of them would put on material supply. The resource-demand plots in the text use the data in these tables. They are based on an imagined scenario: that in order to meet global electric power demand, the capacity of a chosen power system must be expanded by 200 GW per

year (See the Materials for Low Carbon Power White Paper), and to compliment this, 10 hours of storage capacity must be built—meaning 2,000 GW.hr or 7.2 PJ (equal to 7.2 x 106 MJ) of storage capacity per year. The metric for resource pressure

is the mass of each material required for the expansion of the system per year,

, expressed in kg/year divided by the current (2010) global production per year, , also expressed in kg/year.

The plots show this as the percent demand of current production.

The resource demand is not interesting when it is trivial. The plots show the demand on the materials that are deemed to be “critical”, as explained in Section 2, together with other (non-critical) materials whose supply will likely be stretch by large scale implementation of the particular system. Their global annual productions for critical materials in 2010 appear Figure 10. They are marked with an asterisk (*) in the tables below.

Pumped Hydro Storage Material Intensity (kg/MJ)

Aluminum 0.01 Brass 0.0002-0.0014 Chromium* 0.005-0.01 Concrete 60-120 Copper 0.0014-0.0049 Iron 0.60-0.79 Lead 0.0006-0.005 Magnesium 0.0002-0.002 Manganese* 0.0004-0.003 Molybdenum 0.0005-0.004 Plastics 0.012-0.02 Wood 0.16-1.3 Zinc 0.0008-0.01 Total mass, all materials 61-120

Materials and quantities (Tahara et al., 1997), (Pacca & Horvath, 2002), (Vattenfall AB Generation Nordic, 2008) and (Ribeiro & da Silva, 2010).

mI sR

mIx 6102.7

aP

a

ms P

IxR 6102.7=


Compressed Air Energy Storage Material Intensity (kg/MJ)

Carbon steel 0.0084-0.054 Chromium* 0.000006-0.00013 Concrete 1.8-12 Copper 0.00025-0.0016 High Alloy Steel 0.086-0.56 Iron 0.0045-0.029 Manganese* 0.0011-0.0069 Molybdenum 0.000011-0.000069 Plastics 0.00093-0.0060 Silicon 0.00024-0.0015 Vanadium 0.000032-0.00021 Total mass, all materials 1.9-13

Materials and quantities from (Meier & Kulcinski, 2000).

Flywheels Material Intensity (kg/MJ)

Carbon Fiber 1.8 Carbon Steel 12-400 Copper 1-30 Plastics 2-4 YBCO 0.0058-0.17 of which Barium 0.0024-0.07 of which Copper 0.0017-0.051 of which Yttrium* 0.00078-0.023 Total mass, all materials 17-500

Materials and quantities from (Hartikainen et al., 2007).

Thermal Storage Material Intensity (kg/MJ)

Calcium Silicate 0.06-0.12 Carbon Steel 0.78-1.4 Chromium* 0.008-0.03 Concrete 3.1-4.8 Foam Glass 0.041-0.084 Mineral Wool 0.15-0.26 Molten Salt (40% KNO3, 60% NaNO3)

7.1-24

Nickel* 0.0044-0.017 Nitrogen 0.026-0.4 Refractory Brick 0.40-0.62 Silica 0-17 Total mass, all materials 12-48

Materials and quantities from (Heath et al., 2009).


Lead Acid Batteries Material Intensity (kg/MJ)

Antimony 0.055-0.14 Copper 0.017-0.042 Glass 0.11-0.28 Lead 1.4-3.5 Lead oxides 1.9-4.9 Plastics 0.55-1.4 Sulfuric Acid 0.55-1.4 Total mass, all materials 4.6-12

Materials and quantities from (Sullivan & Gaines, 2010).

Lithium-Ion Batteries Material Intensity (kg/MJ)

Aluminum 0.072 Carbon Black 0.075-0.09 Copper 0.13 Ethylene Glycol Dimethyl Ether 0.44 Graphite* 0.47 Lithium Compounds 1.2 of which Lithium* 0.2 Plastics 0.18-0.2 Total mass, all materials 1.5-2.6

Based on Iron Phosphate type Lithium Ion Batteries. Materials and quantities from (Zackrisson et al., 2010).

Sodium-Sulfur Batteries Material Intensity (kg/MJ)

Alumina 0.18-0.63 Aluminum 0.32-1.1 Carbon Steel 0.18-0.64 Copper 0.05-0.17 Glass 0.06-0.22 Graphite* 0.03-0.1 Plastics 0.11-0.4 Silica 0.21-0.76 Sodium 0.11-0.4 Sulfur 0.18-0.63 Total mass, all materials 1.4-5



Nickel-Cadmium Batteries Material Intensity (kg/MJ)

Cadmium 1.1-3.1 Carbon Steel 0.38-1.1 Chromium* 0.091-0.26 Cobalt* 0.06-0.18 Copper 0.18-0.51 Lithium Hydroxide 0.03-0.09 of which Lithium* 0.0087-0.025 Nickel and Compounds 1.6-4.7 of which Nickel* 1.3-3.9 Plastics 0.13-0.39 Potassium Hydroxide 0.22-0.65 Total mass, all materials 3.8-11

Materials and quantities from (Sullivan & Gaines, 2010) and (Gaines & Singh, 1995).

Nickel-Metal Hydride Batteries Material Intensity (kg/MJ)

Carbon Steel 1.2-3.5 Cerium* 0.22-0.64 Nickel and Compounds 0.81-2.4 of which Nickel* 0.66-2.0 Plastics 0.14-0.04 Potassium Hydroxide 0.08-0.24 Total mass, all materials 2.5-6.8


Vanadium Flow Batteries Material Intensity (kg/MJ)

Carbon Black 0.037-0.065 Carbon Steel 0.85-1.5 Copper 0.064-0.11 Graphite* 0.024-0.042 Plastics 0.31-0.54 Sulfuric Acid 2.1-3.6 Vanadium 0.45-0.78 Total mass, all materials 3.8-6.6

Materials and quantities from (Rydh, 1999).


Hydrogen Storage Material Intensity (kg/MJ)

Aluminum 0.03 Carbon Black 0.01 Carbon Steel 1.7 Chromium* 0.09 Copper 0.2 Glass Fiber 0.06 Graphite* 0.24 Molybdenum 0.0007 Nickel* 0.05 Phosphoric Acid 0.02 Plastics 0.04 Platinum* 0.000003 Silicon Carbonate 0.12 Zinc 0.06 Total mass, all materials 2.6

Materials and quantities from (van Rooigen, 2006) and (Nadal, 1997).

Super-capacitors Material Intensity (kg/MJ)

Activated Carbon 12-14 Aluminum 9.8-20 Plastics 1-2.5 Ammonium Salts in Acetonitrile 23-29 Total mass, all materials 45-66

Materials and quantities from (Maxwell Technologies, Inc., 2009) and (Maxwell Technologies, Inc., 2011).

Superconducting Magnetic Energy Storage Material Intensity (kg/MJ)

Carbon Steel 32 Copper 3.8 Sulfuric Acid 0.22 YBCO 0.52 of which Barium 0.21 of which Copper 0.15 of which Yttrium* 0.07 Total mass, all materials 36

Materials and quantities from (Hartikainen et al., 2007).


Further Reading

The starting point—sources that help with the big picture Electricity Storage Association (2009) “Technology Comparison” Electricity Storage Association, Washington, DC USA http://www.electricitystorage.org/technology/storage_technologies/technology_comparison (Accessed 08/11) Harvey, L.D.D. (2010) “Mitigating the adverse effect of fluctuations in available wind energy” in “Energy and the New Reality 2: Carbon-Free Energy Supply” Earthscan Publishing, London UK. ISBN 978-1-84971-073-2 pp. 129-138 House, K.Z. (2009) “The limits of energy storage technology” The Bulletin of Atomic Sciences http://www.thebulletin.org/web-edition/columnists/kurt-zenz-house/the-limits-of-energy-storage-technology (Accessed 07/11) MacKay D.J.C. (2009) “Fluctuations and Storage” in “Sustainable energy – without the hot air” UIT Publishers, Cambridge UK. ISBN 978-0-9544529-3-3 and http://www.withouthotair.com pp. 186-202 Rastler, D. (2009) “Overview of Electric Energy Storage Options for the Electric Enterprise” Electric Power Research Institute, CA USA http://www.energy.ca.gov/2009_energypolicy/documents/2009-04-02_workshop/presentations/0_3%20EPRI%20-%20Energy%20Storage%20Overview%20-%20Dan%20Rastler.pdf (Accessed 08/11) Rastler, D. (2011) “Energy Storage Technology Status” Electric Power Research Institute, CA USA http://mydocs.epri.com/docs/publicmeetingmaterials/1104/4ANZGWRJTYQ/E236208_02._Rastler_Energy_Storage_Technology_Status.pdf (Accessed 08/11) Ribeiro, P.F., Johnson, B.K., Crow, M.L., Arsoy, A. and Liu, Y. (2001) “Energy storage systems for advanced power applications” Proceedings of the IEEE Vol. 89 (12) pp. 1744-1756 Schaber, C., Mazza, P. and Hammerschlag, R. (2004) “Utility-Scale Storage of Renewable Energy” The Electricity Journal Vol. 17 (6) pp. 21-24 Schoenung S.M. (2001) “Characteristics and Technologies for Long-vs. Short-Term Energy Storage” Sandia National Laboratories, CA USA http://prod.sandia.gov/techlib/access-control.cgi/2001/010765.pdf (Accessed 08/11) Schoenung, S.M. and Hassenzahl, W.V. (2003) “Long- vs. Short-Term Energy Storage Technologies Analysis” Sandia National Laboratories, CA USA http://prod.sandia.gov/techlib/access-control.cgi/2003/032783.pdf (Accessed 08/11)

Pumped Hydro Storage Denholm, P. and Kulcinski, G.L. (2004) “Life cycle energy requirements and greenhouse gas emissions from large scale energy storage systems” Energy Conversion and Management Vol. 45 (13-14) pp. 2153-72 Pacca, S. and Horvath, A. (2002) “Greenhouse Gas Emissions from Building and Operating Electric Power Plants in the Upper Colorado River Basin” Environmental Science and Technology, Vol. 36 (14) pp.3194-3200 Ribeiro, F.d.M. and da Silva, G.A. (2010) “Life-cycle inventory for hydroelectric generation: a Brazilian case study” Journal of Cleaner Production, Vol. 18 (1) pp.44-54


Tahara, K., Kojima, T. and Inaba, A. (1997) “Evaluation of CO2 payback time of power plants by LCA” Proceedings of the Third International Conference on Carbon Dioxide Removal, Energy Conversion and Management Vattenfall AB Generation Nordic (2008) “Certified Environmental Product Declaration EPD(R) of Electricity from Vattenfall's Nordic Hydropower” http://www.vattenfall.com/en/file/Environmental_Product_Declara_8459904.pdf (Accessed 08/11)

Compressed Air Energy Storage BINE Informationsdienst (2007) “AA-CAES – Forschungsziele”, http://www.bine.info/hauptnavigation/publikationen/projektinfos/publikation/druckluftspeicher-kraftwerke/aa-caes-forschungsziele/ (Accessed 07/11) Denholm, P. and Kulcinski, G.L. (2004) “Life cycle energy requirements and greenhouse gas emissions from large scale energy storage systems” Energy Conversion and Management Vol. 45 (13-14) pp. 2153-2172 Iowa Stored Energy Park, The (2010) “About The Iowa Stored Energy Park” http://www.isepa.com/about_isep.asp (Accessed 08/11) Knight, M. (2008) “Where to store wind-powered energy? Under water!” CNN, Technology http://edition.cnn.com/2008/TECH/science/03/31/windpower/ (Accessed 08/11) Meier, P.J. and Kulcinski, G.L. (2000) “Life-Cycle Energy Cost and Greenhouse Gas Emissions for Gas Turbine Power” Energy Centre of Wisconsin http://www.ecw.org/prod/202-1.pdf (Accessed 08/11) Messina, J. (2010) “Compressed Air Energy Storage: Renewable Energy” Physorg, Technology, Energy & Green Tech http://www.physorg.com/news188048601.html (Accessed 08/11) Zolfagharifard, E. (2011) “Compressed air energy storage has bags of potential” The Engineer http://www.theengineer.co.uk/1008374.article (Accessed 08/11)

Springs Chiu, C.H., Hwan, C.L., Tsai, H.S. and Lee, W.P. (2007) “An experimental investigation into the mechanical behaviors of helical composite springs” Composite Structures, Vol. 77 (3) pp. 331-340 Hill, F.A., Havel, T.F. and Livermore, C. (2009) “Modeling mechanical energy storage in springs based on carbon nanotubes” Nanotechnology

Flywheels Beacon Power “Frequency Regulation and Flywheels” http://www.beaconpower.com/files/Flywheel_FR-Fact-Sheet.pdf (Accessed 08/11) Collins, P.G. and Avouris, P. (2000) “Nanotubes for Electronics” Scientific American Hartikainen, T., Mikkonen, R. and Lehtonen, J. (2007) “Environmental Advantages of Superconducting Devices in Distrubitued Electricity-Generation” Applied Energy, Vol. 84 (1) pp. 29-38 EFDA JET (2001) “Flywheel Generators” EDFA JET, Oxfordshire UK http://www.jet.efda.org/focus-on/jets-flywheels/flywheel-generators/ (Accessed 08/11)


Flybrid Systems (2011) “Flybrid Systems Website” http://www.flybridsystems.com/ (Accessed 08/11) LaMonica, M. (2008) “One megawatt of grid storage, 10 big flywheels” CNET News, Green Tech http://news.cnet.com/8301-11128_3-9968539-54.html (Accessed 08/11) Lazarewicz, M. and Judson, J. (2011) “Performance of First 20 MW Commercial Flywheel Frequency Regulation Plant” Beacon Power Corporation, CA, USA http://www.beaconpower.com/files/Beacon_Power_presentation_ESA%206_7_11_FINAL.pdf (Accessed 08/11) Peng, B. et al. (2008) “Measurements of near-ultimate strength for multiwalled carbon nanotubes and irradiation-induced crosslinking improvements” Nature Nanotechnology Vol. 3, pp.626-631 Racecar Engineering (2011) “Flywheel hybrid systems (KERS)” http://www.racecar-engineering.com/articles/f1/flywheel-hybrid-systems-kers/ (Accessed 08/11)

Thermal Storage Burkhardt III, J.J., Heath, G.A., Turchi, C.S. (2011) “Life Cycle Assessment of a Parabolic Trough Concentrating Solar Power Plant and the Impacts of Key Design Alternatives” Environmental Science and Technology Vol. 45 (6) pp. 2457-2464 CALMAC (2007) “Thermal Energy Storage – ICEBANK Model C Specifications and Drawings” CALMAC Manufacturing Corporation, NJ, USA http://www.calmac.com/products/icebankc_specs.asp (Accessed 08/11) The Engineering ToolBox “Heat Storage in Materials” http://www.engineeringtoolbox.com/sensible-heat-storage-d_1217.html (Accessed 08/11) Heath, G., Turchi, C., Burkhardt, J., Kutscher, C. and Decker, T. (2009) “Life Cycle Assessment of Thermal Energy Storage: Two-Tank Indirect and Thermocline” American Society of Mechanical Engineers (ASME) Third International Conference on Energy Sustainability, San Francisco Macnaghten, J. (2010) “Electricity Storage Part 3: Isentropic Electricity Storage” Isentropic Ltd, Cambridge, UK http://www.chase.org.uk/files/Isentropic%20ARM%20presentation%20(part%202).pdf (Accessed 08/11) Tamme, R. (2009) “Thermal Energy Storage for Large Scale CSP Plants” DLR – Germal Aerospace Center, Institute of Technical Thermodynamics http://www.srcf.ucam.org/cuens/img/Academic_Material/Tamme_Storage%20CSP.pdf (Accessed 08/11)

Batteries Buchman, I. (2003) “Battery University” http://batteryuniversity.com/ (Accessed 08/11) Conway, E. (2003) “World’s biggest battery switched on in Alaska” The Telegraph, Technology http://www.telegraph.co.uk/technology/3312118/Worlds-biggest-battery-switched-on-in-Alaska.html (Accessed 08/11) Denholm, P. and Kulcinski, G.L. (2004) “Life cycle energy requirements and greenhouse gas emissions from large scale energy storage systems” Energy Conversion and Management Vol. 45 (13-14) pp. 2153-2172 Energizer “Technical Information” Energizer, MO, USA http://data.energizer.com/ (Accessed 08/11)


Gaines, L. and Cuenca, R. (2000) “Costs of Lithium-Ion Batteries for Vehicles” Center for Transportation Research, Argonne National Laboratory, IL USA http://www.transportation.anl.gov/pdfs/TA/149.pdf (Accessed 08/11) Gaines, L. and Nelson, P. (2010) “Lithium-Ion Batteries: Examining Material Demand and Recycling Issues” Argonne National Laboratory, IL, USA http://www.transportation.anl.gov/pdfs/B/626.PDF (Accessed 08/11) Gaines, L. and Singh, M. (1995) “Energy and Environmental Impacts of Electric Vehicle Battery Production and Recycling” Total Life Cycle Conference and Exposition, Vienna, Austria Hartikainen, T., Mikkonen, R. and Lehtonen, J. (2007) “Environmental Advantages of Superconducting Devices in Distrubitued Electricity-Generation” Applied Energy, Vol. 84 (1) pp. 29-38 Haruna, H., Itoh, S., Horiba, T., Seki, E. and Kohno, K. (2011) “Large-format lithium-ion batteries for electrical power storage” Journal of Power Sources Vol. 196 (16) pp. 7002-7005 HILTech Developments Limited (2005) “Vanadium Redox Flow battery – Key Features” HILTech Developments Limited, Sunderland, UK http://hiltechdevelopments.com/uploads/news/id43/vanadium_redox.pdf (Accessed 08/11) Kopera, J.J.C. (2004) “Inside the Nickel Metal Hydride Battery” Cobasys, MI, USA http://www.cobasys.com/pdf/tutorial/inside_nimh_battery_technology.pdf (Accessed 08/11) Lotspeich, C. and Van Holde, D. (2002) “Flow Batteries: Has Really Large Scale Battery Storage Come of Age?” Energy Efficiency Center, University of California, CA, USA NGK Insulators, Ltd. “Principle of the NAS Battery” NGK Insulators, Ltd. Nagoya Japan http://www.ngk.co.jp/english/products/power/nas/principle/index.html (Accessed 08/11) Nicad Power (2010) “Technical Data [of Nickel Cadmium Batteries]” Nicad Power Pte Ltd., Singapore http://www.nicadpower.com/products/technical/ (Accessed 08/11) Rydh, C.J. (1999) “Environmental assessment of vanadium redox and lead-acid batteries for stationary energy storage” Journal of Power Sources Vol. 80 (1-2) pp.21-29 De-Leon, S. (2011) “Li/CFx Batteries, The Renaissance” Schmuel De-Leon Energy, Ltd., Israel http://www.contourenergy.com/technology/presentations/sdl_presentation.pdf (Accessed 08/11) Skyllas-Kazacos, M. “An Historical Overview of the Vanadium Redox Flow Battery Development at the University of New South Wales, Autralia” School of Chemical Engineering & Industrial Chemistry, University of New South Wales, Sydney, Australia http://www.vrb.unsw.edu.au/overview.htm (Accessed 08/11) Sullivan, J.L. and Gaines, L. (2010) “A Review of Battery Life-Cycle Analysis: State of Knowledge and Critical Needs” Energy Systems Division, Argonne National Laboratory, IL, USA http://www.transportation.anl.gov/pdfs/B/644.PDF (Accessed 08/11) Wright, R. (2009) “New battery could change world, one house at a time” Daily Herald http://www.heraldextra.com/news/article_b0372fd8-3f3c-11de-ac77-001cc4c002e0.html (Accessed 08/11) Zackrisson, M., Avellán, L. and Orlenius, J. (2010) “Life cycle assessment of lithium-ion batteries for plug-in hybrid electric vehicles - Critical issues” Journal of Cleaner Production Vol. 18 (15) pp.1519-1529 Zelinsky, M., Koch, J., Fetcenko, M. (2010) “Heat Tolerant NiMH Batteries for Stationary Power” Ovonic Battery Company, MI, USA


Hydrogen Energy Storage Granovskii, M., Dincer, I., Rosen, M.A. (2006) “Life cycle assessment of hydrogen fuel cell and gasoline vehicles” International Journal of Hydrogen Energy Vol. 31 (3) pp. 337-352 Hydrogenics (2010a) “Fuel Cell Power Systems based on PEM technology” http://www.hydrogenics.com/fuel/ (Accessed 08/11). Hydrogenics (2010b) “Hydrogen Generators based on water electrolysis” http://www.hydrogenics.com/hydro/ (Accessed 08/11) Nadal, G. (1997) “Life Cycle Air Emissions from Fuel Cells and Gas Turbines in Power Generation” London: Imperial College of Science, Technology and Medicine, London UK http://www3.imperial.ac.uk/portal/pls/portallive/docs/1/7294736.PDF (Accessed 08/11) US Department of Energy (2011) “DOE Targets for Onboard Hydrogen Storage Systems for Light-Duty Vehicles” http://www1.eere.energy.gov/hydrogenandfuelcells/storage/current_technology.html (Accessed 07/11) van Rooijen, J. (2006) “A Life Cycle Assessment of the PureCell(TM) Stationary Fuel Cell System: Providing a Guide for Environmental Improvement” Center for Sustainable Systems, University of Michigan http://css.snre.umich.edu/css_doc/CSS06-08.pdf (Accessed 07/11)

Capacitors Kim, I.H., Ma, S.B., Kim, K.B. “Super-capacitor” Lab. Of Energy Conversion & Storage Materials, Yonsei University, Seoul, Korea http://web.yonsei.ac.kr/echemlab/public_html/data/sucap.pdf (Accessed 08/11) Maxwell Technologies, Inc. (2009) “Product Guide - Maxwell Technologies BOOSTCAP Ultra-capacitors” http://about.maxwell.com/pdf/1014627_BOOSTCAP_Product_Guide.pdf (Accessed 08/11) Maxwell Technologies, Inc. (2011) “Production Information Sheet #1004596.3” http://about.maxwell.com/ultracapacitors/products/pis.asp (Accessed 08/11)

Superconducting Magnetic Energy Storage ClimateTechWiki “Energy Storage: Superconducting magnetic energy storage (SMES)” http://climatetechwiki.org/technology/jiqweb-ee (Accessed 08/11) Hartikainen, T., Mikkonen, R. and Lehtonen, J. (2007) “Environmental Advantages of Superconducting Devices in Distributed Electricity-Generation” Applied Energy, Vol. 84 (1) pp. 29-38. Schnyder, G. and Sjöström, M. (2005) “SMES” École Polytechnique Fédérale de Lausanne, Switzerland http://lanoswww.epfl.ch/studinfo/courses/cours_supra/smes/Report_18%20SMES.pdf (Accessed 08/11)

Documents

Energy - edisciplinas.usp.br · intensities; material, energy, CO2, capital and land area. Includes Coal and Gas pow- ... 12,000–18,000 . 800–1130 : 35–50 . Tidal, barrage :