Study looks at storing wind energy in Mid-Columbia

By Annette Cary, Tri-City HeraldMay 20, 2013 

Wind energy could be stored underground among volcanic rock formations in two places in Eastern Washington, making the seasonal and intermittent power that wind generates more practical, according to a new study.

Sites north of Boardman in Benton County and about 10 miles north of Selah in the Yakima Canyon could store enough wind energy to power about 85,000 homes each month, according to the study, conducted by Pacific Northwest National Laboratory and Bonneville Power Administration.

About 13 percent of the Northwest's power supply comes from wind. But the supply of wind power and the demand for it are not well-matched.

Mid-Columbia winds blow the hardest in the spring, but that also is when high water makes power from hydroelectric generation abundant. The winds also tend to blow at night, when the demand for power drops as customers sleep.

If the energy could be stored on a large scale, it could be saved for months until it is needed. Or on a smaller scale, it could be used to balance the power supply on the grid, storing and releasing energy during short-term peaks and dips in wind power generation.

Researchers are looking at compressed air storage, a technology that's relatively well understood, according to PNNL. Storage plants in Alabama and Germany use man-made salt caverns to store excess electricity.

But Eastern Washington's geology could provide power storage deep underground without the expense of having to carve out caverns.

Most of the wind farms in southeastern Washington and northeastern Oregon sit on land above the Columbia River Basalt Extent, where lava flows left layers of solid basalt that sandwich other layers with as many holes as a sponge.

The rock could work even more efficiently than salt caverns, said Pete McGrail, a PNNL fellow and lead researcher, when the study was in its early stages 18 months ago.

In typical compressed-air power storage, excess power is used to compress air from 14.7 pounds per square inch in the atmosphere to 1,000 to 2,000 pounds per square inch and push it underground. When power is needed, the compressed air is brought to the surface, heated slightly and used to spin a turbine to produce electricity.

In salt formations, the remaining air depressurizes as compressed air is pumped out. But in basalt layers, water would be pushed out of the way to make a bubble of pressurized air. When the pressurized air is pumped out, the water could collapse back on the remaining air and help maintain pressure.

Researchers narrowed possible sites to underground basalt reservoirs at least 1,500 feet deep, 30 feet thick and close to transmission lines to receive excess power from multiple wind farms and then distribute it after storage, said PNNL spokeswoman Franny White.

The site north of Boardman could access a nearby natural gas pipeline that could supply gas to heat compressed air that's released from underground storage. The heated air would then generate more than twice the power of a typical natural gas power plant, according to PNNL and BPA.

It could store 231 megawatts and would work well for frequent energy storage or could store energy for up to 40 days.

The Yakima Canyon site does not have easy access to natural gas, but researchers propose extracting geothermal heat from deep underground to power a chiller that would cool the facility's air compressors, making them more efficient. Geothermal energy would also re-heat the air as it returns to the surface.

The site could store 150 megawatts and would have the potential for future expansion, according to PNNL and BPA.

BPA, working with the Northwest Power and Conservation Council, next will use performance and economic data from the study to analyze the benefits of compressed air storage. The results could be used by one or more regional utilities to develop a demonstration project.

-- Annette Cary: 582-1533; acary@tricityherald.com; Twitter: @HanfordNews

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