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PG&E to compress air to store wind power

Pacific Gas & Electric says it is applying for stimulus funds to build a compressed-air storage facility able to store as much energy capacity as a medium-size power plant.

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.


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.