Wind plus compressed air equals efficient energy storage in Iowa proposal
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| The Iowa Stored Energy Plant project proposes to use wind energy to compress air for storage in an underground aquifer. When generation is needed, the compressed air would be released to drive natural gas-fired combustion turbines. |
Air in its rapidly moving form, otherwise known as wind, has become an increasingly important part of Iowa's energy mix, and it may become even more important if the Iowa Association of Municipal Utilities succeeds in launching an innovative wind-powered compressed air energy storage facility project.
CAES technology uses off-peak power to store compressed air in an underground aquifer for use in later generation. A joint project of IAMU and a steering committee of municipal utility managers, the Iowa Stored Energy Plant would use wind power to compress the air and an underground aquifer to store it. "Adding renewable energy and a different type of storage space to the equation has the potential to make an already effective technology even more attractive," said IAMU Energy Services Coordinator Patti Cale-Finnegan.
Studies examine how variables might affect CAES
The aquifer is located near Fort Dodge, Iowa, close to the electric transmission grid and a gas pipeline. Part of the facility may be used to store natural gas, making the ISEP of interest to gas as well as electric utilities. Northern Natural Gas originally developed the aquifer for natural gas storage in the 1960s, and it still contains some of the stored gas. "That indicates that it is just as airtight as the caverns used at other plants, maybe more so," Cale-Finnegan stated.
Initial studies suggest another advantage to the aquifer—that compressing air to displace water would require less pressure and therefore less energy. The ISEP proposal includes building a wind farm, using 1.5-MW wind turbines to alternately power the compressor and feed the grid. Preliminary cost estimates show that 200-MW of CAES generation capacity, combined with a 100-MW wind farm, is the most economical configuration. The steering committee has applied for a Department of Energy grant to further study the model.
Wind Utility Consultant Tom Wind, a member of the ISEP steering committee, was the original advocate for incorporating wind energy into the plant. "The two technologies are complementary," he noted. "In a sense, CAES serves as a battery to store the intermittent power the turbine produces, and wind power makes CAES more cost effective. The wind industry is very aware of the project, and we could see others like it in areas with the right combination of storage spaces and good wind resources."
ISEP addresses energy, economic issues
Using wind energy, as well as off-peak electricity, to power the ISEP makes the project more attractive to utility managers who face growing electrical demand, projected capacity deficits and rising natural gas prices. "The ISEP addresses a number of issues, such as renewable portfolio standards, the potential for carbon emissions fines to go up and local economic development," said Kent Holst, steering committee chairman and general manager of Traer, Iowa, Municipal Utility. "These problems are only going to get more pressing. That's why we believe utilities will support this kind of innovative solution."
When the proposal was first presented at an IAMU meeting, the concept generated enough interest to bring the steering committee together. The committee solicited $600,000 in pre-development funds to pay for an economic feasibility study and technical analysis by the engineering firm Burns and McDonald. The studies should be completed during the summer and incorporated into a business plan for presention to utilities this fall.
If the committee can get enough commitments from municipal utilities to own capacity in ISEP, the project could break ground within the next 18 months. The Iowa Public Power Agency a joint financing agency, may serve as the bond issuer for the project.
The operational structure of ISEP has yet to be determined. "We will offer ownership shares to utilities and then to other investors," conjectured Cale-Finnegan, "but the operational schedule could be market driven, with the plant operated by a control area on behalf of the owners. The studies will clarify the options and help us pick the most viable plan."
Whatever business model ISEP uses, the committee anticipates a strong positive response from the local utilities for reasons extending beyond a new source for cleaner, cost-effective power. With a $215 million construction cost and ongoing income from leases of underground aquifer storage rights and for wind turbine placement, "The Iowa Stored Energy Plant would provide an economic benefit for the entire state of Iowa," Holst asserted.
