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• http://edition.cnn.com/CNNI/Programs/eco.solutions/?iref=allsearch
Climate long term average conditions over a region or the planet; averages of temperature & humidity (moisture content of atmosphere) are most important; also cycles over the year
Global Warming & Climate Change
We need some terminology
Weather and climate basics
local immediate conditions of atmosphere (hot, stormy, snowy, rain, hail, wind, hurricane …); fluctuations of conditions around climatic averages; expected to become more severe as temperatures increase (higher temperature more energy more volatility)
Weather
Earth’s temperature has been about 14 °C for 10000 yrs (287 K); but in the last century & especially in the last 25 yrs seems to be rising – we expect 1-2K increase in next century
the effect of rising temperatures & changing humidity on planetary and local environments over time – ecologies will change, extinctions will occur, sea levels will rise as ice caps melt, social upheaval
Global Warming & Climate Change
We need some terminology
Climate Change
Weather and climate basics
Global Warming
evidence, calculations, causes, potential effects, some ways to mitigate problem
efficiency, losses, energy budgets, power generation (fossil fuels and alternatives)
Agenda of Study
Energy Use and Generation
Climate Change & Global Warming
8.1 Objectives
• 8.1.1 State that thermal energy may be completely converted to work in a single process, but that continuous conversion of this energy into work requires a cyclical process and the transfer of some energy from the system.
• 8.1.2 Explain what is meant by degraded energy.• 8.1.3 Construct and analyse energy flow diagrams
(Sankey diagrams) and identify where the energy is degraded.
• 8.1.4 Outline the principal mechanisms involved in the production of electrical power.
8.1 Energy degradation and power generation
1. Hot gas will cause the piston to move
2.But one stroke of the piston does not provide much energy
3.The process needs to be cyclical
Cyclical processes
The continuous production of energy can be obtained from a cyclical process
Not all of the heat can be converted to work
Some is transferred to the surroundings
Efficiency of heat engines
No heat engine can transfer all of it’s energy to work.
Some is always lost as heat to the surroundings.
Equation is not in the syllabus
Generation of Energy
Energy generation for human society takes energy at high temperature
(concentrated), uses some of it, and wastes the rest
at low temperature (dilute, degraded)
Useful work
High T, concentrated E
Low T, dilute, degraded E
Generation of Energy
This is the 2nd Law of Thermodynamics – that we cannot use all the thermal energy available to do useful work – some must be released at low temperature
Useful work
High T, concentrated E
Low T, dilute, degraded E
Generation of Energy
The efficiency is
e = Work outEnergy in_______
Useful work
High T, concentrated E
Low T, dilute, degraded E
Generation of Energy
The maximum efficiency is
emax = 1 –
TCTH/
Useful work
High T, concentrated E
Low T, dilute, degraded E
Generation of Energy
For many reasons (friction, losses) we cannot achieve the best possible efficiency,
but that is the goal
Useful work
High T, concentrated E
Low T, dilute, degraded E
Degradation of energy• Energy flows from hot bodies to cold bodies.• The difference in temperature between two bodies can make a “heat engine” work, allowing useful mechanical work to be extracted in the process.
Some of the thermal energy transferred from the hot to the cold body can be transformed into mechanical work.
• Energy flow between two bodies is represented by a Sankey Diagram.
Generation of EnergyKey to improving efficiency – knowing where
the energy is lost
Sankey diagrams
show energy flows
type of flow diagram, in which the width of the arrows is
proportionate to the flow quantity.
often used to visualize energy or material or cost transfers
Sankey diagrams
You must be able to construct and analyse Sankey diagrams to show where energy is degraded.
100% 25%
Technologies for Generation of Energy
Electric generators and motors are central to energy generationThese work by rotating coils of wire within magnetic fieldsA basic principle of electricity
and magnetism is that a changing magnetic field
creates a changing voltage ( current in a circuit)
Since the coil is rotating the area “seen” by the magnetic field varies (so the field in the coil changes) voltage AC
current
Technologies for Generation of Energy
Hydro generation
model
Water flow converts GPE to KE of water to rotational KE of magnet to PE in B
field to KE of moving electrons to radiant energy of light
click for simulation
Technologies for Generation of Energy
A useful generator or motor has to run on a cycle – it must repeat what it does if we are
to keep generating energy
8.2 Objectives
• 8.2.1 Identify different world energy sources.• 8.2.2 Outline and distinguish between renewable and
non-renewable energy sources.• 8.2.3 Define the energy density of a fuel.• 8.2.4 Discuss how choice of fuel is influenced by its
energy density.• 8.2.5 State the relative proportions of world use of the
different energy sources that are available.• 8.2.6 Discuss the relative advantages and
disadvantages of various energy sources.
Energy Sources
RenewableSolar
GeothermalHydro
Wind
Tidal
Fossil fuels
Nuclear
Non-Renewable
All sources depend ultimately on the Sun, except GeothermalNon-Renewable are Renewable on a very long time scale
CO2 emissions
BioMass
Gas
Oil
Coal
Energy Sources
91% Non-renewable
Energy SourcesNon-renewable energy sources have advantages:
Portable
Energy dense
Controlled use and availability
Solar, wind, tides, geothermal, electric are difficult to carry around & use on a small scale
Renewable sources tend to be diffuse
The sun shines, wind blows, tides rise when & where they do, not when & where we need the energy
Joules of useful energyKilogram of
fuel
Energy density =
Energy SourcesNon-renewable energy sources have disadvantages:
Require storage
Require energy for delivery
Release pollutants health problems global warming
Solar energy pours over us, winds blow, tides rise, trees grow, but the energy derived must be stored or lostRenewable sources
also require delivery by electric grid, usuallyRenewables tend to be
CO2 neutral, but hydro drowns forests and releases gases, solar has manufacturing processes which pollute, wind has ugly mills
Energy density
Energy density is the energy that can be obtained from a unit mass of the fuel. It is measured in J kg-1.
If the energy is obtained by burning fuels, the energy density is simply the heat of combustion.
Substance Heat of combustion
Coal 30 MJ kg-1
Wood 16 MJ kg-1
Diesel oil 45 MJ kg-1
Gasoline 47 MJ kg-1
Kerosene 46 MJ kg-1
Natural gas 39 MJ m-3
Energy density
• In a nuclear fission reaction, mass is converted directly into energy through Einstein’s formula E=mc2.
• For instance, 1kg of pure uranium-235 releases about 7x104 GJ. Natural uranium produces about 490 GJ/kg and enriched uranium about 2100 GJ/kg.
• In a hydroelectric power station, considering that the water falls from a height of 100m the kinetic energy gained by 1kg of the water is 103 J.
• This implies that the energy density of water used as ‘fuel’ is much less than the energy density of fossil fuels.
Energy GenerationEfficiency varies
Source: % efficiency
Oil 40 - 45
Coal 35 - 40
Gas 45 - 50
8.3 Objectives
• 8.3.1 Outline the historical and geographical reasons for the widespread use of fossil fuels.
• 8.3.2 Discuss the energy density of fossil fuels with respect to the demands of power stations.
• 8.3.3 Discuss the relative advantages and disadvantages associated with the transportation and storage of fossil fuels.
• 8.3.4 State the overall efficiency of power stations fuelled by different fossil fuels.
• 8.3.5 Describe the environmental problems associated with the recovery of fossil fuels and their use in power stations.
Energy Source Research
• Investigate two sources and report back to the class. This can be done with a presentation to the class or each of you could produce a maximum of 2 pages on a wiki, for example.
• The text in your presented information must be your own but you can use pictures or diagrams from cited sources.
• Make sure to refer to the objectives in the syllabus to ensure you are meeting the requirements of what you need to know.
• Fossil Fuels, Solar Power, Wind Power, Hydroelectric Power, Wave Power, Biomass/Geothermal
Energy Source Research
• (a) Describe briefly how the energy is produced (mentioning energy density, relative amount used compared to other sources, general efficiency, and more!)
• (b) Discuss the main energy transformation that take place• (c) Construct a Sankey diagram (energy flow diagram) for
the production, identifying where the energy is degraded.• (d) Discuss the relative advantages and disadvantages of
the energy source.• (e) Present an argument for why you think this energy
source is should be utilized.
Fossil fuelsFossil fuels have been created over millions of years.
They are produced by the decomposition of buried animals and plant matter under the combined action of the high pressure of the material on top and bacteria.
Thermal energy produced when burning these fuels is used to power steam engines.
Although these engines are generally efficient (30-40%) they are also responsible for atmospheric pollution and contribute greenhouse gases to the atmosphere.
Fossil fuel mining• Coal is obtained by mining. This process
releases a large number of toxic substances and the coal itself is high in sulphur content and traces of heavy metals.
• Rain can wash away these substances and cause environmental problems if this acidic water enters underground water reserves.
• Drilling for oil has also adverse environmental effects, with many accidents leading to leakage of oil both at sea and on land.
Fossil fuel miningAdvantages• Relatively cheap (while they last)• High power output (high energy density)• Variety of engines and devices use them directly and easily• Extensive distribution network is in place
Disadvantages• Will run out• Pollute the environment• Contribute to greenhouse effect by releasing greenhouse gases
into atmosphere• High cost of distribution due to high mass and volume of materials
and high cost of storing (needs extensive storage facilities)• Pose serious environmental problems due to leakages at various
points along the production
Rate of coal use in a power station
• 1000 MW output of electricity• Coal power stations are 40% efficient• Coal has 29MJ/Kg• Calculate the rate of use of coal• (Approx 300 tonnes/hr)
State the overall efficiency of powerstations fuelled by different fossil
fuels.
• Coal 35 – 42%• Natural Gas 45 – 52%• Oil 38 – 45%
Fossil fuels:
1. are portable
2. have much higher energy densities than most biofuels therefore easier and cheaper to transport(cf wood at ~10 MJ kg-1 with coal at ~20 MJ kg-1)
3. were (and still are) cheap compared to many other sources of energy
4. are widely available (most countries have some fossil fuel resources)
5. may be used directly for heating
6. engines may be small (eg domestic use)
Fossil fuels - origins
Fossil fuels were produced from organic matter over many millions of years due to very high pressures and temperatures.
coal: formed from dead plants on land
oil: formed from dead microscopic marine life
natural gas: formed during production of oil
Efficiencies of power stationsMost power stations which derive their
energy from fuels use heat engines to drive generators to produce electrical power.
The maximum efficiency of heat engines is determined by the operating temperatures of the engine.
Frictional and other losses further reduce this efficiency.
Efficiencies of power stations using fossil fuels
Fuel typical efficiency
coal 35%
natural gas 45%
oil 38%
Fossil fuelsEnvironmental problems
Use of fossil fuels causes environmental damage in two ways:
1. during extraction – coal mining, oil drilling
2. during use
• pollution due to combustion products
• production of greenhouse gases
Research and summarise the environmental problems due to the use of fossil fuels as source of energy – refer to handout notes
Fossil fuelsTransportation and storage
Since fossil fuels are portable and so widely used, how they are transported and stored are key factors in the continuing demand for fossil fuels.
Research and summarise the advantages and disadvantages associated with the transportation and storage of fossil fuels. –refer to handout notes
Gasoline tanker fire – Kenya 2009
Energy Generation by Fossil Fuels
The environment and our health may suffer
Coal particulates, heavy metals, acids produced from sulphur emissions, CO2 all adversely effect the environment
Directly or indirectly they effect our health and food supplies & diminish ecological diversity as some plants and animals suffer
Objectives• 8.4.1 Describe how neutrons produced in a fission reaction may be used
to initiate further fission reactions (chain reaction).• 8.4.2 Distinguish between controlled nuclear fission (power production)
and uncontrolled nuclear fission (nuclear weapons).• 8.4.3 Describe what is meant by fuel enrichment.• 8.4.4 Describe the main energy transformations that take place in a
nuclear power station.• 8.4.5 Discuss the role of the moderator and the control rods in the
production of controlled fission in a thermal fission reactor.• 8.4.6 Discuss the role of the heat exchanger in a fission reactor.• 8.4.7 Describe how neutron capture by a nucleus of uranium-238 (238U)
results in the production of a nucleus of plutonium-239 (239Pu).• 8.4.8 Describe the importance of plutonium-239 (239Pu) as a nuclear fuel.
Objectives
• 8.4.9 Discuss safety issues and risks associated with the production of nuclear power.
• 8.4.10 Outline the problems associated with producing nuclear power using nuclear fusion.
• 8.4.11 Solve problems on the production of nuclear power.
Energy Generation by Nuclear Decay
U – 235 naturally breaks down; but it can be caused to break by slow neutrons
Energy is released – according to E = mc²
With the energy, 2 or 3 neutrons are released as well, going on to break more U – 235 nuclei
U-235 (+ neutron) Ba-141 + Kr-92 + 2 or 3 neutrons + energy
Chain Reactions & Nuclear Energy
To release energy continuously the reaction must be continuous – self-sustaining
U-235 will split (fission) if a neutron collides with it
U-235 (+ neutron) Ba-141 + Kr-92 + 2 or 3 neutrons + energy
Meitner
The neutrons released may go on to split other U-235 nuclei; if the average is greater than 1 more nuclei split for each nuclei split, the reaction runs away – a chain reaction, an explosionThere is a certain amount of material needed to maintain the fission – this is called the critical mass
The Chain ReactionU-235 (+ neutron) Ba-141 + Kr-92 + 2 or 3 neutrons + energy
chain reaction quickly releases vast amount of energy massive explosion,
… unless it is controlled by absorbing neutrons in a moderator (as in a nuclear reactor)
Each neutron can then split a U-235 nucleus 2 or 3 more neutrons
PHeT – Nuclear fission
Chain reactions
Each fission reaction releases neutrons that are used in further reactions.
Fast neutronsNeed to be slowed down
Critical mass?
nKrBanU 10
9236
14256
10
23592 2
Nuclear reactors
• Uranium-235 will only capture neutrons if they are not too fast. The neutrons produced in the chain reaction are too fast to be captured and have to be slowed down (they have to go from 1MeV of kinetic energy to less than 1 eV).
• The slowing down of neutrons is achieved through collisions of the neutrons with atoms of the moderator, a material surrounding the fuel rods (tubes containing U-235). The moderator can be graphite or water, for example.
• The rate of reaction is determined by the number of neutrons available to be captured by U-235.
To few neutrons would result in the reaction stopping
Too many neutrons would lead to an uncontrollably large release of energy.
Nuclear reactors
• Thus, the control rods (the material that can absorb excess neutrons whenever necessary) are introduced in the moderator.
• The control rods can be removed when not needed and reinserted when necessary again.
• The control rods ensure that the energy from nuclear reactions is released in a slow and controlled way as opposed to the uncontrollable release of energy that would take place in a nuclear weapon.
Describe what is meant by fuelenrichment.
Natural U-235 occurs as 0.7% abundance. (3300C)
Enriched fuel contains 2.3% U-235, therefore increases the temperature (6000C) of the core of the reactor, therefore increases the efficiency and power output/Kg
Nuclear power station
Nuclear Power Plant
Fission is moderated by control rods which absorb excess neutrons
The splitting of U-235 Ba-141 + Kr-92 + 2,3 neutrons + energy
Each neutron can then split a U-235 nucleus 2,3 more neutrons
Energy absorbed by working fluid (heavy water or sodium, pink)
Cooling water (turquoise) cools steam generation water Working fluid heats water to form steam (blue) driving turbine electricity
graphite moderator
boron control rod
heat exchanger
fuel element channel
steel
concrete
hot gas
reactor core
cold gas
charge face
Magnox Nuclear Reactor
The moderator “slows” their speed.
Nuclear reactors• In a Pressurized Water
Reactor (PWR) water is kept under pressure to keep it from boiling, even at 300 C.
• The pressurized water is pumped through a closed system of pipes called the primary circuit.
• Heat from the primary circuit warms up water in the secondary circuit.
• The water in the secondary circuit comes to a boil and its steam turns the turbine.
• The water in the primary circuit returns to the reactor core after giving up some of its heat.
Nuclear reactors• Gas Cooled Reactors
(GCR) use carbon dioxide as the coolant to carry the heat to the turbine, and graphite as the moderator.
• Like heavy water, a graphite moderator allows natural uranium (GCR) or slightly enriched uranium (AGR) to be used as fuel.
http://www.cameco.com/uranium_101/uranium_science/nuclear_reactors/
Magnox nuclear power station
Three Mile Island nuclear power station
http://www.solcomhouse.com/nuclear.htm
Describe the main energytransformations that take place in a
nuclear power station.
EK of fission fragments
Hyperlink
Technologies for Generation of Energy
Energy flow in Nuclear Reactors
Mass-energy of U – 235 nuclei KE of fission products thermal energy of working fluid KE of steam turbine electrical energy via magnetic inductionheating via heat exchanger of coolant
Nuclear reactors
• The energy released in the reaction is the form of kinetic energy of the produced neutrons (and gamma ray photons).
• This kinetic energy is converted into thermal energy (in the moderator) as the neutrons are slowed down by collisions with the moderator atoms.
• A coolant (e.g. water or liquid sodium) passing through the moderator can extract this energy, and use it in a heat exchanger to turn water into steam at high temperature and pressure.
• The steam can be used to turn the turbines of a power station, finally producing electricity.
nuclear energy
kinetic energy of particles
thermal energy
kinetic energy of rotation
electrical energy
Example
• Suppose that the average power consumption for a household is 500 W per day. Estimate the amount of uranium-235 that would have to undergo fission to supply the household with electrical energy for a year. Assume that for each fission, 200 MeV is released.
Discuss the role of the moderator and the control rods in the production of controlled fission in a thermal fissionreactor.
graphite moderator
boron control rod
heat exchangerfuel element channel
steel
concrete
hot gas
reactor core
cold gas
charge face
The moderator slows the neutrons down to enable them to allow fissions
The control rods absorb neutrons to control the power level
The heat exchanger isolates the water from the coolant and lets the hot gas boil the water.
What are the energy transformations?
Plutonium production• The fast neutrons produced in a fission reaction may be used
to bombard U-238 and produce plutonium-239.• This isotope of plutonium does not occur naturally.• The reactions are:
UUn 23992
23892
10 eNpU 0
123993
23992
ePuNp 01
23994
23993
• The importance of these reactions is that non-fissionable material (U-238) is being converted to fissionable material (Pu-239) than can be used as the nuclear fuel in other reactors.
Fast breeder reactors• The U-238 is
converted to Pu-239• The Pu-239 is
fissionable by fast neutrons
• Therefore, the reactor can breed its’ own fuel
• Doesn’t need a moderator (saves space)
• Very high operating temperature, cooled by liquid sodium
Use of plutonium
The waste from conventional nuclear reactors is processed to recover Pu-239 and unused U-235.
Pu-239 readily absorbs fast neutrons so does not need a moderator to enable fission – used in fast-breeder reactors.
Nuclear EnergyAdvantages• High power output• Large reserves of nuclear fuels• Nuclear power stations do not produce greenhouse
gases
Disadvantages• Radioactive waste products difficult to dispose of• Major public health hazard should ‘something go wrong’• Problems associated with uranium mining• Possibility of producing materials for nuclear weapons
Uranium mining
• Like all types of mining, uranium mining is dangerous.
• Uranium produces radon gas, a known strong carcinogen as it is an alpha emitter.
• Inhalation of this gas as well as of radioactive dust particles is a major hazard in the uranium mining industry.
• Mine shafts require good ventilation and must be closed to avoid direct contact with the atmosphere.
• The disposal of waste material from the mining processes is also a problem since the material is radioactive.
Problems with nuclear reactors
• Both fuel and products of the reactions are highly radioactive, with long half-lives. Disposal of nuclear waste is a serious disadvantage of the fission process in commercial energy production.
• This material is currently buried deep underground in containers that are supposed to avoid leakage to the outside.
• Another problem is the possibility of accidents due to uncontrolled heating of the moderator.
• Such heating would increase in temperature and hence the pressure in the cooling pipes, resulting in a explosion.
• This would lead to the leakage of radioactive material into the environment or, even worse, could lead to the meltdown of the entire core.
Nuclear fusion
• A typical energy-producing nuclear fusion reaction is:
MeVnHeHH 6.1710
42
31
21
• Deuterium (D) can be extracted from water using electrolysis and tritium (T) can be produced by bombarding lithium with neutrons.
• The problem with fusion is that, since D and T are both positively charged, the reacting nuclei repel.
• To get them close enough to each other for the reaction to take place, high temperatures must be reached – around 108 K.
• At this temperature, hydrogen atoms are ionized and so we have a plasma (mixture of positive nuclei and electrons).
Nuclear fusion
• The hot plasma must be confined in such way so that it doesn’t come into contact with anything else as this would cause:
a reduction in temperature
contamination of the plasma with other materials.
• These two effects would cause the fusion reaction to stop.
• The plasma is therefore confined magnetically in a tokamak machine (toroidal magnetic chamber).
• The magnetic field prevents the plasma from touching the container walls.
Nuclear fusion
• Energy must be supplied to the fusion process to reach the high temperatures required.
• It has not yet been possible to produce more energy out of fusion that has first been put in, for sustained periods of time.
• For this reason, fusion as a source of commercially produced energy is not yet feasible.
• Compared to nuclear fission, nuclear fusion has the advantage of plentiful fuels, substantial amount of energy produced and much fewer problems with radioactive waste.
Quick ReviewDescribe a chain reaction in U-235. How is the chain reaction controlled to produce power safely? What is a major problem with nuclear power?
In U-235 a slow moving neutron may disrupt the nucleus, causing it to split (fission) producing daughters (Ba-141 & Kr-92), energy and 2 or 3 more neutrons, each of which can split another U-235 nucleus; thus the process is exponential and goes very quickly if not controlled. In reactors, a moderator is used to absorb neutrons and keep the reaction from becoming explosive and cooling water is used to remove the energy for power production. A major problem associated with nuclear power is the disposal and storage of nuclear waste, chiefly Pu-239 a highly active long-lived toxic material.
• When one uranium nucleus fissions about 200 MeV of energy is released. In 235 g of Uranium there are 6.023 x 1023 atoms. A 100 MW nuclear power station is 34.0% efficient. What mass of Uranium undergoes fission every second when the power station output is a maximum?
• Each fission releases 200 x 106 x 1.6 x 10-19 or 3.2 x 10-11 J. The energy needed each second from the fissions is 100 MW/0.34 or 294 MJ s-1.
• The number of fissions needed per second is 294 x 106/3.2 x 10-
11 or 9.19 x 1018 fissions/s.• The mass of 9.19 x 1018 U atoms is 235 x 9.19 x 1018/6.023 x
1023 or 359 g
Example
Objectives
• 8.4.12 Distinguish between a photovoltaic cell and a solar heating panel.
• 8.4.13 Outline reasons for seasonal and regional variations in the solar power incident per unit area of the Earth’s surface.
• 8.4.14 Solve problems involving specific applications of photovoltaic cells and solar heating panels.
• 8.4.15 Distinguish between different hydroelectric schemes.• 8.4.16 Describe the main energy transformations that take
place in hydroelectric schemes.• 8.4.17 Solve problems involving hydroelectric schemes.
Objectives
• 8.4.18 Outline the basic features of a wind generator.• 8.4.19 Determine the power that may be delivered by a
wind generator, assuming that the wind kinetic energy is completely converted into mechanical kinetic energy, and explain why this is impossible.
• 8.4.20 Solve problems involving wind power.• 8.4.21 Describe the principle of operation of an oscillating
water column (OWC) ocean-wave energy converter.• 8.4.22 Determine the power per unit length of a wavefront,
assuming a rectangular profile for the wave.• 8.4.23 Solve problems involving wave power.
Technologies for Generation of Energy
Solar Power
Convert insolation (radiant energy, photons) to electric current
Nature does it well – photosynthesisWe do it with silicon panels, germanium,
exotic metals and. lately, in research, chlorophyll, like plants
Solar Energy
Average insolation for most people is from 150 to 300 W/m².Shows land area (black dots) required to replace the world primary energy supply with solar energy. (18 TW is 568 Exajoule (EJ) per year)
source: http://en.wikipedia.org/wiki/Solar_power
Solar Energy Main technologies
Concentrated Solar Power (CSP)
Solar cooking tacos – click for video
Solar Energy Main technologies
Solar Panel
Si & Ge are semiconductors – do not conduct well unless “encouraged”
photons encourage them by supplying energy to “boost” electrons “up” freeing them from metal and creating a current
Union of Concerned Scientists
Solar Energy Main technologies
Solar energy heats water passing thru collector, which may be used for heat, hot water supply
Union of Concerned Scientists
SynthesisDescribe energy transformations in a generic solar energy system.
PV - Radiant energy (as photons from Sun) is concentrated (CSV) to heat working fluid; hot fluid drives steam turbines KE electricity, via EM induction
CSV - Radiant energy (as photons from Sun) striking semi-conductor “lift” electrons, thru photoelectric effect (h KE, PE). Electrons form current passing thru system (electrical energy released)
SP - Radiant energy (as photons from Sun) heats water (h thermal energy) which is used directly
SynthesisDescribe potential problems of solar technologies.
Most useful in mid-latitudes, not N or S
PV – manufacturing is polluting, expensive; cells are fragile & of low (but increasing) efficiency
PV, CSV – Land area large compared to fossil fuel plants, expensive or far from market
Energy available at wrong time – mid-day, but greatest need is later; requires expensive storage and more robust (expensive) transmission grid
Technologies for Generation of Energy
Wind Power
Convert energy of moving air to electricity
We do it with large, hi-tech windmills
Technologies for Generation of Energy
Wind Power Driving gear; must be robust (to withstand high wind-speed) Computer controlled to change direction as wind changes and govern speed of rotation to maximize energy output
SynthesisDescribe advantages and disadvantages of wind technologies.
Only useful where there is much steady air flow, not hurricanes
Land hungry, and not generally considered esthetic
Expensive, requires subsidies to match fossil fuels (but fossil fuels are subsidized too in the form of no charge for pollution and no charge for global warming, yet)
Only work when the wind blows, which may not be when needed – energy storage needed.
Wind is free as long as it blows
Wind is clean, no direct pollution from energy generation
Wind technology is new and requires creativity and design innovation enhances economy and creates opportunities
Technologies for Generation of Energy
Hydro Power
Convert GPE of falling water to electricity
We do it with large, hi-tech earth and concrete dams & electromagnetic induction
Click for video
SynthesisDescribe advantages and disadvantages of hydro power.
Most useful on large, fast flowing rivers – these often have major other uses – Yangtze (3 Gorges Dam), or are far from use (James Bay & New York)
Land hungry (floods large areas or forest and farm)
Releases CO2 from decaying vegetation
Water energy is free if available
Hydro is clean, no direct pollution from energy generation
Hydro is settled science; so the investment costs are relatively low per unit power
Disrupts ecosystems (salmon migration) changes climate up and downstream
Effects water quality, siltation of reservoir stops renewal of fertility downstream
Technologies for Generation of Energy
Wave PowerConvert KE & GPE of tides and waves to electricity
Click for video
Click photos for websites
SynthesisDescribe advantages and disadvantages of tidal / wave power.
Only useful where there are large tides or strong waves
Very cutting edge; not settled science and not cheap
Hard on equipment
Wave and tide energy are free if available
Clean, no direct pollution from energy generation
Disrupts sea bed ecology
SynthesisDescribe advantages and disadvantages of alternative energy
Expensive currently
Not usually in synch with actual power needs; high energy when demand low and vice versa
Some needs considerable basic research and engineering yet
Relatively free sources of energy, derived from Sun (+ geothermal)
Relatively clean, no direct pollution from energy generation
Needs subsidies and fossil fuel companies have lobbies to slow that down
8.2.6 Discuss the relative advantages and disadvantages of various energy sources.
No pollution Hazazard to low flying aircraft
Self starting NoisyTall towers can be built almost anywhere Structural failure due to fatigue
WindAdvantages Disadvantages
Cheap Difficult to transport large components
Minimal maintenance Large areas of land neededSunlight inconsistentOperating costs low
Pollution free operation Expensive to set upProduction wastes manageable Energy loss converting the DC to AC
Advantages DisadvantagesSolar
TidalAdvantages Disadvantages
Low running costs Fish mortality rate of about 15% per pass
Peak output time varies during lunar month
Pollution free when operating. Very expensive to set up
More efficient than solar and fossil fuels Do not produce power all day80% efficiency Limited number of suitable sites
Many needed to replace a ff power stationEyesore on the scenic coast line
Pollution free when operating.
Has to work in gentle seas
Location vital - need consistent wavesExpensive set up - must withstand storms
Variable output - waves inconsistent
WaveAdvantages Disadvantages
Low running costs Can be noisy - silencer needed
ReliableSmall amounts of fuel needed Slight chance of major explosion
No smoke or CO2 - no greenhouse effect Wastes must be sealed and buried
Small amounts of waste Wastes remain dangerous for many years
NuclearAdvantages Disadvantages
Not expensive - about the same as coal Wastes are very radioactive - dangerous
Contribute to acid rainReliable
Cheap Likely to contribute to global warmingSimple burning process Prices depend on politics
Advantages DisadvantagesEasily obtained and distributed Produces the greenhouse gas CO2
Fossil
Pollution free when operating. Natural habitats destroyed by dam water
HydroelectricAdvantages Disadvantages
Low running costs Water storage takes up large areas.
Renewable energy sources summary
Wind, tidal, hydroelectric and solar
Advantages Disadvantages
Zero fuel costs
Hydroelectric is good for a
“sudden” demand
Don’t produce pollution
Tidal barrages destroy the habitats of wading birds and hydroelectric
schemes involve flooding farmland
Unreliable (except for
hydroelectric)
Expensive to build
Solar is good for remote locations (e.g. satellites)
Non-renewable energy sources
Coal, oil, gas and nuclear
Advantages Disadvantages
Cheap fuel costs
Short start-up time for gas and oil
Good for “basic demand”
Fuel will run out
Costs a lot of money to
decommission a nuclear plant
Pollution – CO2 leads to global warming and SO2 leads to acid rain
Reliable
Nuclear produces little pollution
