Buzz
The Iowa Stored Energy Park, scheduled for completion in 2011, is expected to cost between $200,000 and $225,000, excluding the price of wind turbines and infrastructure. View images of wind energy installations.Wind energy offers numerous advantages. It is a renewable power source driven by the sun, our planet's natural furnace. It generates electricity without emitting harmful greenhouse gases.
Moreover, wind energy is free from hazardous by-products such as mercury or nuclear waste.
However, wind energy faces challenges that limit its widespread use. The wind is not always reliable, and it often blows when demand is low. But what if we could capture and store the surplus energy produced by wind farms for future use?
This concept is at the heart of the Iowa Stored Energy Park (ISEP). Here, energy is stored as compressed air, with the Earth serving as the storage medium, not a battery. This is not some futuristic vision—compressed air energy storage (CAES) has been in use for years, though it is now gaining more attention from environmentalists and renewable energy advocates searching for greener alternatives to fossil fuels.
How does it all function? Keep reading to discover more.
Acronyms, like the wind, are a consistent part of any conversation about the Iowa Stored Energy Park. Here are some key terms to know:
ISEP – Iowa Stored Energy Park. The "P" used to stand for "Plant," but it was changed to "Park" when the organization was established in 2005.
ISEPA – Iowa Stored Energy Park Agency. Formed under section 28E of Iowa’s code, ISEPA represents over 130 municipal utilities across Iowa, Minnesota, and the Dakotas.
CAES – Compressed Air Energy Storage. CAES stores energy by compressing air in an underground cavern. During high demand periods, this air is released to generate power using a turbo-generator system.
IAMU – Iowa Association of Municipal Utilities. IAMU represents more than 550 municipal utilities (electric, gas, water, and telecommunication) across Iowa. It’s the largest organization of its kind in the U.S.
What is the Iowa Stored Energy Park?
The Iowa Stored Energy Park will generate electricity through wind turbines. Excess wind energy will power a compressor, and the compressed air will be stored in sandstone underground for later use.The idea for ISEP was introduced in 2003 when members of the Iowa Association of Municipal Utilities (IAMU) formed a study committee to investigate how wind energy could be creatively harnessed to enhance the state's power production.
Iowa ranks as the third largest wind energy producer in the U.S., trailing only California and Texas. To further cement its leading position, the IAMU study committee realized that adding another massive wind farm, even with cutting-edge turbines, wouldn't suffice on its own. They recognized the need for an energy storage solution. Therefore, they proposed a power plant combining a 100-megawatt wind farm and a compressed air energy storage system.
The ISEP concept is inspired by two operational CAES facilities: one in Huntorf, Germany, managed by Nordwest Deutsche Kraftwerke since 1978, and the other in McIntosh, Alabama, operated by Alabama's Electric Cooperative since 1991. These facilities store compressed air underground, with the Huntorf facility utilizing salt caverns and the McIntosh facility leveraging existing mines.
The ISEP planning group considered testing the storage of compressed air in an aquifer. An aquifer is a natural underground rock layer capable of holding water due to its numerous tiny gaps between rock and gravel particles, which trap water. Surprisingly, this rock is also suitable for storing air. When compressed air is pumped into an aquifer under high pressure, it behaves like a giant bubble, displacing groundwater. After months of study, the committee identified an aquifer near Fort Dodge, Iowa, that seemed perfect. It was close to both the electric transmission grid and a gas pipeline, but ultimately, the site was deemed unsuitable for several reasons.
As the team expanded its search for other potential sites, it also underwent some organizational changes. In 2005, responsibility for ISEP was handed over to the Iowa Stored Energy Park Agency (ISEPA), a corporation in Iowa representing more than 130 municipal utilities across Iowa, Minnesota, and the Dakotas.
In January 2007, after two years of thorough evaluation, the agency finalized its site selection process, choosing a location just west of Dallas Center in central Iowa. This site proved to be ideal for multiple reasons. The aquifer, located 3,000 feet (914 meters) below the surface, is both deep and expansive, making it capable of storing a substantial amount of air. Additionally, the site's geological features are favorable, with layers of porous sandstone topped by dense shale, which allows both air and water retention. Furthermore, the site’s proximity to downtown Des Moines, approximately 30 miles (48.3 km) away, is advantageous for potential economic development and tourism, which could attract more visitors.
While the Dallas Center location is suitable, it does not offer the best wind conditions in Iowa. As a result, ISEPA is exploring the possibility of a remote wind farm. This farm may either be developed by ISEPA itself or in collaboration with an existing private wind farm. Regardless, wind energy will play a pivotal role in the project. Unlike the Huntorf and McIntosh plants, which rely on off-peak electricity from traditional nuclear or coal-fired power plants to operate their compressors, ISEP will use wind-generated electricity to power the compressor and send any surplus energy back to the grid. By combining CAES and wind power, ISEP aims to provide a sustainable and environmentally friendly energy source for both homes and businesses.
In the upcoming section, we will delve into the process by which ISEP will generate electricity.
ISEP and Electrical Generation
Combustion turbines generate electricity by burning a mixture of fuel and air. However, most of the energy produced in this process is absorbed by the processor, rather than being used to generate electricity in the turbines.While wind energy plays a significant role in ISEP, it will not entirely eliminate the need for fossil fuels in energy production. Instead, it will decrease the reliance on fossil fuels to generate electricity. To grasp why, let's first look at how a conventional turbine power plant operates, which primarily uses natural gas as its energy source.
A conventional turbine power plant consists of a three-part combustion turbine. The first section, the compressor, pulls in air and compresses it. In the second section, the combustion system burns a mixture of fuel and air, producing a high-temperature, high-pressure gas stream. This gas stream moves through the third section, where it spins rotating blades. These blades serve two purposes: they power the compressor and drive a generator to produce electricity. Interestingly, most of the energy in a combustion turbine is used to operate the compressor, not to generate electricity.
Compressed Air Energy Storage (CAES) enhances the efficiency of gas turbines by separating the compression process. Off-peak electricity powers a motor that forces air into an underground reservoir. During high demand periods, the compressed air is released from storage and directed into the combustion system of a gas turbine. Since the air is already compressed, the turbine doesn’t need to run its compressor, allowing all the energy to be used for operating the generator. As a result, significantly less natural gas is consumed.
ISEP takes this concept further by combining wind energy—a clean and renewable resource—with underground storage in an aquifer. The diagram below illustrates how ISEP will function. Let's walk through the process:
- Wind turbines on a farm capture the energy of moving air and convert it into electricity.
- Some of this electricity, especially during peak demand, is sent to the power grid.
- The surplus electricity is directed to a compressor, which pumps air deep underground.
- The air is stored in porous sandstone. As pressure builds, the air pushes groundwater aside like a massive bubble. In essence, the sandstone acts as a battery that can store up to 20 weeks' worth of air.
- During the day or when demand peaks, compressed air is drawn from storage and fed into the combustion system of a gas turbine. The air combines with natural gas, and the fuel-air mixture is burned at extremely high temperatures. The turbine consumes 50% less natural gas because it doesn't have to run the compressor.
- The turbine powers a generator, which produces electricity.
- This electricity is then distributed to homes and businesses.
ISEPA is still in the process of determining the most effective solution for wind energy production, with the goal of completing the preliminary design by May 2008. By September, the agency plans to begin obtaining the necessary permits from the Iowa Utilities Board. The facility is expected to be operational and generating electricity by 2011. Once up and running, ISEP could account for up to 20 percent of the annual energy usage of a typical municipal utility in Iowa. Additionally, it could save cities and utilities as much as $5 million per year in energy costs [source: Energy Services Bulletin].
Utilities across the country are closely monitoring ISEP, with some even starting their own CAES projects. In West Texas, TXU Energy is collaborating with Shell WindEnergy to build a 3,000-megawatt wind farm integrated with a CAES system that will store air in underground salt domes. Other potential sites are being considered in New Mexico and along the Gulf Coast. Whether utilizing salt caves or aquifers, CAES could be the key to making wind energy a significant part of the U.S. electricity supply. The Electric Power Research Institute predicts that over 85 percent of the U.S. has the geological conditions necessary for this technology. One day, a nationwide network of CAES facilities combined with wind power might provide as much as 10 percent of America's electricity [source: BusinessWeek].
