Jump to: Small Wind Systems | Transmission | Wind Storage | Cash Crop | Renewable Portfolio Standard | Connecting to the Grid | Net Metering

Compressed Air Energy Storage (CAES)

I think that it is important for all states to look at their alternative energy generation resources and ways of storing energy. Compressed air energy storage is definitely one. John Turner, National Renewable Energy Laboratory

Each year, Texas generates more electricity from wind than any other state. While researchers have discovered the secret to pulling kilowatts out of wind in the Lone Star State, they are still looking for an economical way to make that power source available at any time. A new process could make that feasible.

The CAES process uses caverns left behind when miners finish mining and clearing salt domes. Electric power utilities can take off-peak electricity from the grid to power a motor/generator that drives compressors to force air into the airtight underground cavern, which is used as a storage reservoir. The air is held 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 combustion turbines that power a generator. Electricity created by the generator can then be delivered to customers.

The CAES process typically occurs when utility system demands and electricity costs are the lowest. When electric power demand peaks during the day, at peak times, the process is reversed. The compressed air is returned to the surface, heated by a small amount of natural gas in combustors and run through high-pressure and low-pressure expanders to power the motor/generator to produce electricity. In conventional gas-turbine power generation, the air that drives the turbine is compressed and heated using natural gas, but CAES requires less gas to produce power during periods of peak demand because it uses air that has already been compressed and stored underground. Using wind initially to compress the air cuts in half the amount of natural gas needed to operate the plant.

Source: Imperial College London, Large-Scale Energy Storage Systems

The concept of compressed-air energy storage to help generate electricity is more than 30 years old. Two plants currently exist - one in Alabama , the McIntosh Project, and the other in Germany, both in caverns created by salt deposits. Neither plant uses wind, but both use electricity generated in periods of low demand to pump air into underground storage. In January 2007, the U.S. Department of Energy (DOE) announced that DOE and a group of municipal utilities in Iowa and surrounding states are collaborating to integrate a 75- to 150-megawatt wind farm with compressed air energy storage. DOE has provided $2.9 million in funding and the technical expertise of the DOE Sandia National Laboratories for the project which should be completed by 2011. The Iowa Stored Energy Park (ISEP) would be the first plant in the world to use energy from a wind farm plus supplemental off peak electricity to produce compressed air to be stored in an underground aquifer until it is need to produce electricity on demand. See this ISEP project update with illustrations, and this article with CAES Demo animation.

SECO's Compressed Air Energy Storage Study

Energy storage can transform an intermittent, renewable energy resource into one that has firm capacity value and that can be dispatched in accordance with load and market prices for energy. Ridge Energy Storage & Grid Services L.P., 2005

Each year, Texas generates more electricity from wind than any other state. While researchers have discovered the secret to pulling kilowatts out of the wind in the Lone Star State, they still working on a way to make that power source available at any time. On average, wind farms operate at peak capacity only about 30 percent of the time. That drops even lower during the hottest summer days in Texas, when wind drops at the same time electricity demand surges. As a result, a wind-power provider must arrange a backup supply from another generator or rely on the Electric Reliability Council of Texas (ERCOT) to buy power to make up for a shortfall, which can get expensive during peak demand.

To address wind energy transmission constraints in areas such as McCamey, the Texas State Energy Conservation Office (SECO) conducted a CAES study to determine what benefits CAES would have for the transmission challenges in these areas. Excess power could be used to pump air underground for later use in generating electricity.

Summary Results, June 2005
The study was able to show significant benefits from the use of CAES to integrate large quantities of wind energy onto the grid. In particular, the study was able to show that CAES can add value in the following ways:

• significantly improve the delivery profile of renewable energy to the grid.
  
  
• ameliorate the impacts of wind energy on system ramping.
  
  
• provide transmission benefits in excess of the cost of any transmission upgrades required by the CAES plant itself.

Full report: Economic Impact of CAES on Wind in TX, OK, and NM

Additional Resources

The industry can forecast the output of a wind farm within 3 percent over 20 years, but it can't predict whether, or how much, the wind will blow next Tuesday. All of these challenges - low pricing for power, limited capacity payments, inefficient transmission use, and poor forecasting abilities - collectively limit the role wind energy can play in power generation today. David Marcus, CEO, General Compression

TXU, Shell to Harvest Panhandle's Wind Energy July 2007
TXU Corp.'s generating subsidiary and Shell WindEnergy plan a huge Panhandle wind farm that could include the use of compressed air to generate electricity when there's not enough wind to spin the big turbines. Greg Wortham, director of the West Texas Wind Energy Coalition in Sweetwater, said the use of compressed air to balance the unpredictability of wind power represents what he called the industry's "holy grail" -- the ability to store wind energy so that it is available on demand, just like electricity from traditional power plants that rely on natural gas, coal and nuclear energy.

Site for ISEP Development is Officially Announced December 2006
ISEP will combine the underground storage of air with energy derived from wind power in Iowa, making the project doubly attractive as Iowa strives to further the advancement of wind energy. Some of the energy collected by wind turbines will drive compressors to push the air underground. ISEP will provide 268 megawatts of CAES generating power and plans to use approximately 75 megawatts of wind power. Also see Capturing the Wind.

Wind Energy Storage
An article presented by the U. S. Department of Energy (DOE), National Renewable Energy Laboratory.

Optimization of a Wind CAES Power System
A Princeton University presentation with several charts and graphs depicting the CAES process.

Case Studies: Energy Storage Technologies
A DOE web page describing several energy storage methods.

Energy Storage: the Emerging Nucleus
This is an article published in the January/February issue of the Distributed Energy magazine.

Store Wind Power for Later Use? Cities Bet on It
An MSNBC article.

Grid Energy Storage
A Wikipedia encyclopedia article.

Send comments, questions, and suggestions to website manager.

Window on State Government | Privacy and Security Policy | Accessibility Policy