TO CATCH THE WIND

A brief chat with John Bilsten of the Iowa Wind Energy Park (see Wind Storage?) confirmed the intent of the project, which is to extend the economically viable energy capacity of Algona Municipal Utilities. Bilsten talked about a variety of forms of energy. “We will continue to diversify our portfolio of generation. We are about the people of Iowa. They want us to do the right thing and that includes being stewards of the land." A little-explored dimension of energy development, Bilsten's project intends to make wind energy more economically viable by storing off-peak generation in the form of compressed air at very low prices and reselling it during peak demand at higher prices. And it is also developing ways to use compressed air stored wind energy in conjunction with biofuels, making both more economically viable.

Here's more on the subject from around the web:

SECO (State Energy Conservation Office) in Texas published findings as of June, 2005:
Compressed Air Energy Storage
- …SECO conducted a study to determine what benefits compressed air energy storage (CAES) would have for the transmission challenges…Air is stored in airtight salt domes to be used later to generate electricity…
- The CAES process uses caverns left behind when miners finish mining and clearing salt domes…generators compress air into the cavern and hold it under pressures between 1,000 and 1,500 pounds per square inch (PSI). By comparison, scuba tanks hold air at about 3,000 PSI. When electricity demands are greater than wind generation, plant operators bring air from the cavern back to the surface, where it is heated with natural gas, causing it to expand and rush through turbines that power a generator. Electricity created by the generator can then be delivered to customers. Because the air has already been compressed, less gas is needed to produce power during periods of peak demand…
- The study was able to show significant benefits…CAES can add value [by]…significantly [improving] the delivery profile of renewable energy to the grid…[ameliorating] the impacts of wind energy on system ramping…[providing] transmission benefits in excess of the cost of any transmission upgrades required by the CAES plant itself.

Also from the Texas site:

Improving the technical, environmental and social performance of wind energy systems using biomass-based energy storage
Paul Denholm, National Renewable Energy Lab (August, 2005)
- [Abstract:] A completely renewable baseload electricity generation system is proposed by combining wind energy, compressed air energy storage, and biomass gasification. This system can eliminate problems associated with wind intermittency and provide a source of electrical energy functionally equivalent to a large fossil or nuclear power plant. Compressed air energy storage (CAES) can be economically deployed in the Midwestern US , an area with significant low-cost wind resources. CAES systems require a combustible fuel, typically natural gas, which results in fuel price risk and greenhouse gas emissions. Replacing natural gas with synfuel derived from biomass gasification eliminates the use of fossil fuels, virtually eliminating net CO2 emissions from the system. In addition, by deriving energy completely from farm sources, this type of system may reduce some opposition to long distance transmission lines in rural areas, which may be an obstacle to large-scale wind deployment.

A Department of Energy evaluation of the concept concludes:
- CAES is really a hybrid storage/power production system. The system stores compressed air that is fed into a natural-gas-fired combustion turbine, allowing the turbine to operate at high efficiency. At present, the only existing CAES systems are combined with large central-station power plants. However, the technology could potentially be applied to distributed energy by using a small air compression station with a gas cylinder that feeds a single combustion turbine or a modified microturbine. The case study presented here is of the only CAES facility in the United States at present.

The D.O.E. page links to:

Facts about the Nation's First Compressed Air Energy Storage (CAES) Power Plant
- Second commercially owned [CAES] in the world. World's first CAES plant is a 290 MW facility located in Huntdorf, Germany.
- First CAES plant in the United States.
- First in the world to use fuel-efficient recuperator, which reduces fuel consumption by 25 percent.
- One full charge from the 110 MW CAES plant provides enough electricity to supply the demands of 11,000 homes for 26 hours.

- Off-peak electricity is used to compress air in the cavern. Top of solution-mined salt cavern is 1,500 feet underground. Bottom of cavern is 2,500 feet underground.
- 10-million-cubic-foot air storage cavern is 220 feet in diameter and 1,000 feet tall.
- At full charge, air pressure is 1,100 pounds per square inch. At full discharge, cavern air pressure is 650 pounds per square inch.
- The cavern walls do not move as the pressure changes inside. The cavern walls have a strength of 50 times that of the maximum air pressure produced by the CAES plant. Compressed air flows through the CAES plant generator at a rate of 340 pounds of air per second, which is as fast as a wide-body jet engine.
- The fuel consumption during generation is equal to 4,600 Btu (HHV) per kilowatt-hour (kWh) of electricity. There are about 20,750 Btu in each gallon of gasoline.
- The electricity consumed during compression is 0.82 kWh of peak load generation.

There is also, on the Texas site, a link to a superb Princeton University powerpoint presentation:
Toward optimization of a wind/compressed air energy storage (CAES) power system

Also:

Compressed air wind energy storage
Bryce Finley, 27 November 2005 (Energy Bulletin)
- Certainly, two of the hurdles to relying on wind power for producing energy are the intermittent nature of the wind itself, and the fluctuating prices producers get for feeding the resulting power into the grid.
- One minute the wind is blowing (at a high enough rate to make power) and the next it isn’t…sometimes when the wind is blowing, power is selling for the lowest possible price, and when the turbines are still, power is worth the most…
- While wind power generation may be the fastest growing segment of the renewable energy business…Building wind farms is expensive, and relying on them to generate either a sufficiently steady source of power for the world - or revenue for the operator - is a sketchy affair…
- Systems for storing wind energy created when the going is good and releasing it for use when the turbines aren’t humming are being worked on…
- In a 2003 paper entitled “Large Scale Energy Storage Systems”, six students of engineering at Imperial College London noted that compressed air energy storage (CAES) systems typically relied on plants burning fossil fuels to compress the air stored in large underground caverns, which then used this air to produce energy at peak hours…
this air was mixed with natural gas and itself burned in a turbine to create the electricity…
- The researchers also noted that another approach, called compressed air storage (CAS) would hold the compressed air in man-made vessels…A few years later, this is exactly the road now being taken by…a Vancouver, B.C. company, Encore Clean Energy Inc…
- Encore will make use of its core technology, the Magnetic Piston Generator (MPG), as the turbine for its wind energy storage systems…MPG is a unique pressure-driven linear engine designed to generate electricity with higher fuel efficiency and lower emissions than conventional internal combustion engine-powered electric generators or even hydrogen fuel cells…The MPG can use many different sources of energy - one of them the compressed air from these proposed wind energy storage facilities - to generate the pressures required to propel the MPG's "Magnetic Piston" at high velocities, back-and-forth, through a linear alternator to generate power according to Faraday's Law of Induction…There are difficult engineering tasks associated…These problems include the high pressure needed for commercially meaningful output and the resulting low temperatures of the air if not reheated.
- Compressing the air in the first place, at least, is not one of the problems Encore envisions…
- if a wind facility made a certain amount of power at non-peak times, only about 25% of it would be used in compressing the air in the first place, leaving 75% of the initial production available for resale later at higher prices [so] “…non-peak intermittent wind power generated at…3-cents/kWh…sold during peak-demand times at prime peak prices of >10-cents per kWh…[generates]…a 250% improvement in gross revenues…”
- “This retrofit wind energy storage solution should enable wind farm owners to earn the highest prices for the power they generate and give local utilities the kind of peak, on-demand, power availability that Utilities pay the most for, but which up until now, current wind farm owners could not reliably guarantee…”

See also: General Compression

And, from energy expert Robert Rapier:

Compressed Air Energy Storage
- I have always been a big fan of wind power. But one of the knocks on wind is that it is intermittent….I have seen it claimed that 2,000 megawatts of installed wind energy still requires 1,800 megawatts of standby power for when the wind isn’t blowing…
- Clearly a storage system is needed…Imagine my surprise this weekend to learn that while I have been daydreaming about a wind energy storage system, someone is in the process of doing it…Members of the Iowa Association of Municipal Utilities have invested in a proposed power plant that would use wind turbines to drive compressed air into underground aquifers. The air would be released to generate electricity when needed…
- The plant will use power from its own wind turbines, supplemented by cheaper electricity bought at off-peak times, to force air into rock formations at least 2,000 feet underground.
- Current plans call for pressurized storage of tens of billions of cubic feet of air in rock formations deep underground…Only two other underground compressed air plants are in operation. A plant in Huntorf, Germany, was built more than 23 years ago and a plant in McIntosh, Ala., is 11 years old. Both store compressed air in underground salt caverns.
- Iowa's project is unique in that it would use wind power to store the air and combine it with massive underground storage capacity.

- The Germany and Alabama plants store hundreds of thousands of cubic feet of air in a thermos-bottle shaped container installed in the salt mines. The Iowa project would use naturally occurring pockets embedded in sand or sandstone formations sealed by shale or other rock…
- You need some kind of large, airtight, underground cavern. There are a lot of these in the United States, but they need to be located near a source of wind. Although, now that I think about it, I see no reason such a system couldn’t also be paired with solar or tidal generation systems, storing their excess energy using the same concept…
- The [Iowa] plant is scheduled to come online in 2010. I wish them great success, and look forward to hearing reports after they start up.