The Northwest's geology holds the potential to offer a cavernous storage bank for excess energy on the regional power grid, according to a broad study released this week.
Researchers with the Pacific Northwest National Laboratory and the Bonneville Power Administration believe the vast, porous underground basalt formations of eastern Washington and Oregon could provide relief for a transmission system sometimes strained by too much supply.
The plan: Use storage plants to pump energy into the ground in the form of compressed air. The conversion would work two ways, allowing managers to deposit energy when it's not needed, and withdraw it when it is. The study even developed conceptual designs for two large-scale facilities in Washington to make that happen at a practical cost.
The findings give credence to a concept that's been used elsewhere, but remains relatively unproven here.
"We definitely have the geology in the Northwest that could work," said Steve Knudsen, a BPA project manager involved in the study. "In a number of ways, it works even better."
The only existing compressed air energy storage plants are in Alabama and Germany. Both use man-made salt caverns. The energy bank concept is also used in the natural gas storage facilities that are common across the country.
A new outlet for energy storage could have big implications for a Northwest power grid strained by a still-growing forest of wind turbines sending new energy into the system. Managers can balance wind generators' output against the more steady hydroelectric dams in the region, but not always. The BPA has at times ordered wind farms to shut down to avoid overloading the grid in recent years.
If energy storage pans out, the federal power marketing agency may have a new relief valve at their disposal.
"It has the potential to take the pressure off the hydro system over time," Knudsen said.
Here's how it works: Compressed air energy storage plants would take on the extra power produced by wind farms, for example, and use that energy to pump compressed air into a huge bubble underground -- keeping it off the rest of the power grid when it's not needed. When generation is low, the plants would release some of that pressurized air back out of the ground, using it to produce electricity through the same turbines.
The facilities could have a recovery rate of as much as 80 percent -- that is, they could re-generate 80 percent of the power they take off the grid.
"Effectively what you're doing is you're converting excess energy," said PNNL laboratory fellow Pete McGrail said. "You're essentially converting that into fuel that you can use later."
The two facilities envisioned by researchers would use two different designs. The so-called Columbia Hills Site, located on the Washington side of the Columbia River just north of Boardman, Ore., would pair compressed air storage with a natural gas power plant. The Yakima Minerals Site, about 10 miles north of Selah, would combine compressed air with geothermal technology.
The Columbia Hills facility would hold an energy storage capacity of 231 megawatts, according to the study. The Yakima Minerals facility would hold up to 150 megawatts of energy.
Researchers believe the concept could pencil out financially, as well. The estimated capital cost of the Columbia Hills site is about $207 million, according to the study. The Yakima Minerals plant could be built for about $176 million. And operation costs would be comparable to other energy facilities, McGrail said.
"The important point is the economics," McGrail said. "You have to have the right geologic structure, but that structure has to be in the right location that's conducive to other needs."
Compressed air isn't the only method of energy storage under development in the Northwest. BPA and PNNL researchers are also test driving a mobile battery storage unit developed by a Tualatin, Ore., company.
The $790,000 compressed air study was funded by the BPA's Technology Innovation Office, PNNL and several other project partners. Researchers will continue to analyze the idea, which could develop into a demonstration project before it's pursued on a larger scale.