Think of it as a giant energy bank. Withdraw when you need it; deposit when you don’t.
The concept has been used before, most notably in the natural gas storage facilities that are common across the country. But a group of researchers led by the Richland-based Pacific Northwest National Laboratory and the Bonneville Power Administration are exploring whether that idea can be put to use in a different form. The goal: storing excess energy in the form of compressed air and water in the Northwest’s expansive, porous underground basalt formations.
Researchers are a long way from proving that it’s doable here, or that it makes financial sense to pull the trigger. But if successful, the concept could have big implications for a Northwest power grid strained by an ever-growing forest of wind turbines pumping new energy into the system.
“The ultimate objective is to be able to store and shape and shore up renewable energy resources like wind,” said Steve Knudsen, a BPA project manager helping with the study, which began last fall. “You would use it essentially as a load to soak up and store excess wind energy.”
Excess energy has been a problem in the past. Just last year, unusually high flows in the Columbia River Basin put the region’s hydroelectric dams at maximum capacity. The situation led to a well-publicized dust-up between the BPA and the region’s wind generators when the BPA ordered them to shut down to avoid overloading the grid. Wind farms objected. A Federal Energy Regulatory Commission decision last December ruled in their favor.
If the concept pans out, BPA and PNNL researchers are hoping the new form of energy storage helps alleviate similar over-generation events.
“The compression takes that load,” said PNNL laboratory fellow Pete McGrail.
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 technology has the potential to regenerate more than 75 percent of the energy that was used for storage, McGrail said.
A second method would use a similar concept to pump water into the ground in a sort of enhanced geothermal system, again banking energy for later use. The two ideas are being studied concurrently. They may even be able to work together under the right conditions, McGrail said.
The concept would need a lot of room to work — researchers are thinking in the neighborhood of 10 million cubic meters of underground storage, McGrail said.
It’s unclear whether wind generators themselves will weigh in on the study. PNNL hasn’t actively reached out to developers so far. Two major national wind players, Iberdrola Renewables and Horizon Wind Energy, also maintain corporate offices in the Northwest.
At least two other examples of air compression energy storage exist in the U.S. and Germany, Knudsen said. But the idea hasn’t been applied on such a large scale in the Northwest’s unique landscape. If it’s feasible, however, it could theoretically absorb all the wind energy generated on the BPA grid over about a week, Knudsen said.
“If you tried to do that with batteries, it would take a battery complex the size of a small city,” he said, noting compressor plants would have relatively little above-ground impact.
Potential seismic impacts aren’t a big concern, McGrail said. The study focuses mostly on eastern Washington and Oregon, where seismic activity is generally quiet.
The $790,000 study, with half paid by BPA and half by cost-share participants, is still in its early stages. Researchers are using computer models and existing geologic data to explore possibilities. The yearlong research project is expected to wrap up late this year.
So is it feasible? The jury’s still out.
“I’m much more encouraged about the technical feasibility than I was maybe at the outset,” McGrail said.
Whether it’s economically feasible, however, is another matter entirely. Researchers haven’t yet drawn up cost estimates for any potential storage system.
“That’s definitely the million-dollar question,” McGrail said.