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Local Government Commission



An Energy Newsletter for Local Governments

Iowa Utilities Propose A Wind-Powered Energy Storage Plant

A group of municipal utilities in Iowa are proposing to build a unique power plant that will combine wind power with a compressed air energy storage (CAES) facility. The proposed Iowa Stored Energy Plant (ISEP) will use a 100-megawatt wind power facility to pump air into an underground aquifer, compressing the air. During times of peak power demand, the compressed air will be supplied to 200 megawatts of combustion turbines that are fired with natural gas, allowing the turbines to operate at high efficiencies. The group places the cost of the ISEP at $215 million and hopes to launch the project this fall, with a startup date in mid-2006.

CAES plants work by replacing a combustion turbine's compressor with a source of compressed air. Nearly two-thirds of the natural gas supplied to a conventional combustion turbine is used to drive the compressor, so a CAES plant burns much less natural gas than a conventional combustion-turbine plant.

ISEP Background:

The centerpiece of the Iowa Stored Energy Plant is compressed air energy storage (CAES). CAES is a technology to store energy in the form of compressed air in an underground facility for use in later generation. CAES is in use in two other locations, a 290-megawatt plant in Germany and a 110-megawatt plant in Alabama, and is a well-known and cost-effective generation technology. A 2,700-megawatt CAES plant has also been proposed by CAES Development Company, LLC for construction in Norton, Ohio.

The Iowa Stored Energy Plant project proposes two innovations to the CAES concept:

First, the compressed air will be stored in an underground aquifer, rather than in a cavern as in other CAES projects.

Second, wind energy will be used to compress air, in addition to the off-peak power used elsewhere.

When generation is needed, the compressed air is released to drive natural gas-fired combustion turbines. The compressed air reduces the need for 2/3 of the natural gas normally used in a turbine.

A separate section of the underground aquifer will also be used for storing natural gas. Gas storage will allow the facility and other gas utilities to buy natural gas when prices are lower.

Preliminary cost estimates show that a configuration of 200 megawatts of CAES generation capacity with a 100-megawatt wind farm is the most economical. Although wind energy is the lowest-cost new generation option available, it is not reliable by itself. CAES acts as a “battery” for wind energy and makes it a dispatchable electrical resource.

Wind PowerWhile the Iowa Stored Energy Plant incorporates wind directly into its design, it will also indirectly promote the use of wind energy in the region. CAES will be operated to follow loads and fill in where other generation is unavailable or uneconomical. Wind generation output is highly variable, but CAES can fill in the gaps for wind. This could expand the role of wind in the region's generation mix.

The combination of natural gas and wind for electric generation lowers carbon emissions significantly and uses the abundant Iowa wind resource. In the future, a carbon neutral power plant, replacing natural gas with shelled corn, another important Iowa resource, can be envisioned.

Although sites in other states are being explored for CAES, Iowa is in the forefront of stored energy development. First, Iowa possesses a site that is ideal for the CAES power plant and wind farm. An underground aquifer near Fort Dodge contains the dome structure, capacity, and porosity needed for storage of both compressed air and natural gas. Second, Iowa has vast wind resources and corn acres.

Income from leases of underground aquifer storage rights and for placement of wind turbines would give local landowners an ongoing revenue stream. At a $215 million construction cost, the Iowa Stored Energy Plant would provide an economic benefit not only for the Fort Dodge area, but for the entire state of Iowa.


Patty Cale-Finnegan
Energy Services Coordinator
Iowa Association of Municipal Utilities

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