Despite all the talk about needed breakthroughs in batteries, Pacific Gas & Electric is pursuing a less high-tech approach to store wind power: underground compressed air.
The utility on Wednesday said that it is seeking $25 million in smart-grid stimulus funds to build an underground compressed-air storage facility that would be able to deliver as much electricity as a medium-size power plant for about 10 hours.
(Credit:
PG&E)
PG&E said the project is part of its smart-grid initiative and would take about five years to develop and build but, in a company blog post, didn't offer any other details on the proposal.
With compressed-air energy storage (CAES), air is compressed and then pumped in natural underground reservoirs. The air is released later and converted into electricity.
There are currently two compressed-air energy storage facilities in operation--one in Alabama and one in Germany--but the technique has been getting more attention because it is a relatively cheap approach to storage.
Utilities are starting to use flywheels to smooth out fluctuations on the grid or truck-size batteries to provide backup power for a couple of hours for a single substation.
CAES is well-suited to an intermittent source of energy like wind because a large amount of energy can be stored for many hours. PG&E's proposal calls for storing 300 megawatts worth of power for 10 hours, while most utility storage batteries being tested are 1 or 2 megawatts for shorter periods.
PG&E said that it plans to use wind turbines to compress the air during off-peak times and then draw from the reservoir during peak times. Shifting the energy from off-peak to peak times, such as the middle of the day, makes it more valuable as utilities pay more for energy at peak times. A wind farm in Iowa has been working on CAES storage for a few years to take advantage of peak pricing for wind.
PG&E quoted a Princeton University study on CAES that concluded that "CAES appears to have many of the characteristics necessary to transform wind into a mainstay of global electricity generation."
Industry executives say that the most cost-effective utility storage is pumped hydro, where water is pumped uphill and released at peak times to make electricity.
This technique, which has been around for decades, is tough to beat on cost. But like compressed-air storage, it requires that utilities find the suitable geography.
Updated at 12:45 p.m. PT to clarify the capacity and energy storage of the facility.
A New Jersey company said on Tuesday it will invest $20 million over three years to develop an underground compressed-air storage system for wind turbines and other power sources, a sign of growing confidence in the technology.
Energy Storage and Power is a joint ventured formed by energy developer PSEG Global and Michael Nakhamkin, who designed the only compressed air-storage facility in the U.S.
With Compressed Air Energy Storage (CAES), air is pumped into underground formations, such as depleted natural gas wells or salt caverns, using a natural gas-powered machine. The pressured air is released later to drive a turbine to make electricity.
A diagram of a compressed air storage facility. Click on the image to see a photo gallery of different grid energy storage technologies.
(Credit: CAES Development Company)The system allows for several hours or even days of stored energy, which allows power producers to deliver electricity during peak hours when the demand for electricity--and price--is highest.
The two CAES plants in operation right now--one in McIntosh, Ala., and the other in Huntorf, Germany--use several hours of storage to generate electricity during the middle of the day.
Energy Storage and Power said that it intends to develop equipment for storing renewable power resources at a large scale. Utilities are already using more wind and solar, but energy storage means that they can be used more broadly since electricity can be "dispatched" as needed.
"We have learned a lot since building the McIntosh plant in Alabama, and I believe the time is right technically, environmentally, and economically for a large-scale deployment of Energy Storage and Power's CAES technology," Nakhamkin said in a statement.
It's not the only commercial company pursuing compressed-air storage of wind energy.
General Compression is designing a wind turbine that has a compressor built into the nacelle, the housing at the top of a wind turbine tower. The company hopes to test a machine with utilities in the next few years.
With the growing use of renewable energy on the power grid and a push toward energy efficiency, energy storage is getting serious attention from investors and utilities.
Lithium-ion battery company A123 is working with utility AES on grid-tied energy storage devices. These 1- or 2-megawatt devices can be used to stabilize the grid's frequency and store enough power for less than an hour.
One advantage of CAES technology is that it can be used for longer periods. The Iowa Stored Energy Park plans to use a natural gas compressor in conjunction with a wind farm that it expects to go online in 2011.
Updated at 12:51 p.m. PT with corrected reference to peak demand time.
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