PHYS 1110

Lecture 26

Professor Stephen Thornton

December 6, 2012

The Last Lecture

Reading Quiz

The utility poles on the street where you live do not likely carry which of the following?

A)Cable TV.B)Telephone lines.C)7200 VAC power lines.D)240 VAC power lines.E)135 kVAC power lines.

Reading Quiz

The utility poles on the street where you live do not likely carry which of the following?

A)Cable TV.B)Telephone lines.C)7200 VAC power lines.D)240 VAC power lines.E)135 kVAC power lines.

Remaining schedule:

Thursday, Dec. 6: HW 8 on Ch. 11 due

Final Exam, Wednesday, Dec. 12, 2-5 pm

Quiz 3 Average was 69.0 19

Go over the quiz.

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Teaching Evaluation Question

I found that separating into groups, discussing a subject, and making a group report made me more engaged in the class.

A)Strongly agreeB)AgreeC)NeutralD)DisagreeE)Strongly disagree

Teaching Evaluation Question

I found that using clickers to answer questions during the class made me more engaged in the class.

A)Strongly agreeB)AgreeC)NeutralD)DisagreeE)Strongly disagree

Need stored energy because of inconsistency of wind and solar. Also need to balance frequency and voltage of electrical grid.

A significant challenge is to learn how to integrate the variability of wind power in the electric grid. The ramp rates of a wind farm in Texas are shown. Energy storage must play a large role in balancing the electrical grid operations due to these large variations of up to 1000 MW. Currently, fossil-fuel generated power is serving that need.

• Pumped hydroelectric storage• Compressed air energy storage (CAES)• Batteries• Flywheels• Superconducting magnetic energy storage

(SMES)• Electrochemical capacitors• Thermal storage• Hydrogen storage

Types of Energy Storage

The increase in non-pumped hydro storage energy over the next decade is expected to increase by a factor of 100!

One factor that helps the situation is if all the electricity produced is connected to the smart grid. Electricity needs are greatest during the day, and solar energy helps provide that. But the amount of electrical energy produced varies by many factors including time of day, season, and weather. If all sources of electrical energy are connected to the grid, then the fact that the wind is not blowing in Kansas is helped by the fact that it is a particularly sunny day in Southern California (solar). The grid allows the energy produced in California to be slightly shifted towards Kansas. But there will still be times when operators will need to find extra electrical energy on short notice without starting up old inefficient, power plants. There are both short term and long term needs. And when both wind and sun are available, that extra electrical energy needs to be stored for that rainy day. The problem of keeping the grid voltage at 120 V and 60 Hz is particularly challenging in small, regional areas like on islands, for example Hawaii. Wind and solar energy will need to be backed up by short term storage energies even to keep the power stabilized. Even more storage capabilities will be needed to supplant peak demand times.

Stored energy is used when the consumed load power exceeds the generated power available.

We can distinguish energy storage in several ways. One simple way is by the technological process:

•Mechanical: Compressed air energy storage, pumped hydro storage, flywheels.•Chemical: Electrolyses, substitute natural gas, fuel cells.•Electrochemical: Batteries of many kinds.•Electrical: Double layer capacitors, super capacitors, and superconducting coils.•Thermal: Warm water storage, latent heat accumulator, thermochemical storage, fluid salts, compressed air energy storage.

We can distinguish energy storage by the time response: short term (seconds, minutes) and long term (minutes, hours):

Short term: Flywheels, cranking batteries, electrochemical capacitors, superconducting magnetic energy storage (SMES).Long term: Pumped hydro storage, compressed air, batteries

Energy storage retrieval time as a function of power.

• Pumped hydroelectric storage – skip here• 2 Compressed air energy storage (CAES)• 5 Batteries – big group, divide up batteries• 3 Flywheels• 1 Superconducting magnetic energy storage

(SMES)• 2-3 Electrochemical capacitors• 3 Thermal storage• Hydrogen storage – skip here

Divide into groups, discuss, and make report

Second generation CAES takes advantage of advanced techniques to burn fuel like natural gas using compressed air.

The Hydrogen Economy

The hydrogen economy is a system by which energy is carried and delivered by hydrogen. The vision of the hydrogen economy is to use hydrogen as a low-carbon energy “source” that would replace gasoline for transport fuel or natural gas as a heating fuel. When hydrogen reacts with oxygen from air to produce electricity, the only byproduct is fresh water. But hydrogen is not an energy source, it is an energy carrier.

We have an electron economy, hydrocarbon economy, and now a proposed hydrogen economy.

Hydrogen fuel cells operate by combining hydrogen and oxygen in an electrolyte and produces electricity (see Ch. 6).

Hydrogen fuel cells offer lots of advantages. They are about twice as efficient in producing heat as the internal combustion engine. Fuel cells have no moving parts; only water and air move around. This leads to less maintenance. Fuel cells have low emissions, and they can generate electricity at their point of use, so electrical transmission lines may not be needed. But a hydrogen gas transmission system probably would be needed. Automobiles operated by hydrogen fuel cells would increase the efficiency of cars and reduce air pollution at the same time. Several car manufacturers have produced prototypes. The hydrogen fuel cell produces electricity which drives the electric motor of the car.

Comparison of efficiency utilizing electricity directly for an electric car (86%) or by using electricity to produce hydrogen gas for use in a fuel cell (25%).

President George W. Bush announced the prospect of the hydrogen economy in his State of the Union address in January, 2003 when he proposed the FreedomCar and FreedomFuel Initiative. Jeremy Rifkin published a book titled The Hydrogen Economy in 2002 in which he extolled the promise of the hydrogen economy by stating “The road to global security lies in lessening our dependence on Middle East oil and making sure that all people on Earth have access to the energy they need to sustain life. Weaning the world off oil and turning toward hydrogen is a promissory note for a safer world”. Rifkin is an economist, writer, political advisor, and activist. He is not a scientist, and many of his books have been attacked because of his lack of scientific rigor. An article in Time magazine in 1989 about Rifkin was entitled “The Most Hated Man in Science”.

The promise of the hydrogen economy is tantalizing and includes

•The elimination of fossil fuels and their associated pollution.•The elimination of global climate change caused by greenhouse gases.•The elimination of economic dependence from unstable countries for their oil and gas.•Possible elimination of much of our energy transportation system. Hydrogen can be produced anywhere it is needed with electricity and water.

But we need to take a more deliberate approach to how the hydrogen economy would actually work. There are a couple of issues of the hydrogen economy that we need to address:

•Methods of producing hydrogen gas•Storage and transport

Producing hydrogen gas

• Electrolysis of water• Reforming• Photocatalytic water splitting• Photobiological water splitting

Hydrogen is primarily used for the production of ammonia NH3 and eventually fertilizer. Hydrogen is produced globally from natural gas (48%), oil (30%), coal (18%) and water electrolysis (4%). So 96% of the current hydrogen gas production also produces carbon dioxide!

Hydrogen is the most abundant element in the universe. However, it almost doesn’t exist by itself on Earth, because it is so light that it escapes gravity and goes to outer space. Hydrogen exists in molecules like methane (CH4), so it has to be transformed into hydrogen gas.

All the hydrogen gas currently produced is from reforming or electrolysis. We do not want to use fossil fuels to generate the electricity for the electrolysis of water. We would want to use renewable energy or nuclear power to do this so we do not release carbon dioxide into the atmosphere. Otherwise, that would defeat the whole purpose of the hydrogen economy! And in the reforming process we are using fossil fuels as the source of hydrogen, but this method adds carbon to the atmosphere which makes the greenhouse gas problem worse.

This leaves only surplus wind energy at night and nuclear power as a reasonable choice to produce hydrogen gas by electrolysis unless some remarkable breakthroughs occur. Nuclear power has the problems we discussed in Chapter 10, but we did discuss its use in the hydrogen economy.

One of the touted advantages of the hydrogen economy is to provide energy using fuel cells for cars and trucks. But hydrogen normally exists in molecular compounds and after transforming to a gas, it would have to be stored. It would be expensive and even possibly dangerous to liquefy hydrogen gas for storage in a car. About 5% would be lost by vaporization each day for safety reasons. That leaves high pressure hydrogen gas storage as the primary option. It would have to stored at very high pressures (200-800 atm), which would require considerable energy. Hydrogen gas compressed to 800 atm pressure occupies three times the volume of gasoline for the same energy output. The mass of the storage tanks required for high pressure hydrogen gas cars would add considerable mass to the car and reduces fuel economy. Another possibility is storage together with metal hydrides, which is currently under research and development, but is not yet available. An example is storage in solid form with sodium borohydride, which Chrysler has been testing.

Hydrogen would have to be made available to the consumer in much the same way as gasoline and diesel fuels are now at service stations beside roads and highways. Unless we are able to produce hydrogen gas at the more than one hundred thousand service stations in the US alone, a system of hydrogen transportation infrastructure would have to be developed. Studies have indicated that current natural gas pipelines might be suitable for both storing and transporting hydrogen gas, but most countries do not have a surplus of natural gas pipelines. Hydrogen causes steel to become embrittled. Natural gas pipelines would require an internal coating before being able to transport hydrogen. There are currently only 1000 km of hydrogen pipelines in the United States.

Fuel cell vehicles are currently much more expensive than conventional vehicles and hybrids. Fuel cells are not yet as durable as the internal combustion engine. It takes about 1 kg of hydrogen to replace the energy of 1 US gallon (0.04 m3). It requires about 55 kW of DC electricity to liberate 1 kg of hydrogen from 9 kg of water by electrolysis. If we use steam reforming of methane (natural gas), it requires only 4.5 kg of water, but 5.5 kg of CO2 is generated. If we use coal, 3 kg of coal and 9 kg of water are needed, but then 11 kg of CO2 is released and must be sequestered.

Comparison of the useful transport energy for an automobile powered by hydrogen or electricity.

It is not efficient to produce, compress or liquefy, transfer, and store hydrogen. The advantage of electric cars over hydrogen fuel cell cars is clear in the previous slide. The touted advantages of the hydrogen economy touted in the early 2000s do not make economic sense according to many experts. It may have been a mistake to announce and begin the Presidential Initiative before a full understanding was in hand. The technology itself makes sense, but the implementation is not cost effective. But don’t completely give up! Chemists and biologists are working hard to produce hydrogen gas from sunlight. A big breakthrough would change everything!

Quiz

Which of the following is not an advantage of AC over DC power?

A)Electrical generators naturally produce AC.B)It is not possible to transmit DC power.C)Transformers only operate by AC, not DC.D)It is easier to convert AC to DC than vice versa.

Quiz

Which of the following is not an advantage of AC over DC power?

A)Electrical generators naturally produce AC.B)It is not possible to transmit DC power.C)Transformers only operate by AC, not DC.D)It is easier to convert AC to DC than vice versa.

Quiz

Which of the following is considered a long term energy storage method?

A)Lead-acid batteryB)SupercapacitorsC)NaS batteryD)Pumped hydroE)Flywheels

Quiz

Which of the following is considered a long term energy storage method?

A)Lead-acid batteryB)SupercapacitorsC)NaS batteryD)Pumped hydroE)Flywheels

Quiz

Which of the following is not considered a reason for energy storage?

A)Provide nuclear waste backup powerB)Balancing energy systemsC)Helping with intermittent windD) Helping with cloudy daysE)Balancing electrical operations on Hawaii

Quiz

Which of the following is not considered a reason for energy storage?

A)Provide nuclear waste backup powerB)Balancing energy systemsC)Helping with intermittent windD) Helping with cloudy daysE)Balancing electrical operations on Hawaii

Quiz

Which of the following is considered the most mature/commercial energy storage operation?

A)Li ion batteriesB)CAESC)SupercapacitorsD) FlywheelsE) SMES

Quiz

Which of the following is considered the most mature/commercial energy storage operation?

A)Li ion batteriesB)CAESC)SupercapacitorsD) FlywheelsE) SMES

Quiz

Which of the following is not considered an advantage of the hydrogen economy?

A)Hydrogen fuel cells are twice as efficient as the internal combustion engine.B)Low emissionsC)Possibly reduced transportation infrastructureD) Fuel cells produce only electricity and waterE) Fuel cell driven cars are more efficient than electric vehicles.

Quiz

Which of the following is not considered an advantage of the hydrogen economy?

A)Hydrogen fuel cells are twice as efficient as the internal combustion engine.B)Low emissionsC)Possibly reduced transportation infrastructureD) Fuel cells produce only electricity and waterE) Fuel cell driven cars are more efficient than electric vehicles.

Good luck with final exams and have a Happy Holiday!