A project in south Texas could unlock a new method of long-term energy storage—essential for a grid powered ever more by intermittent, renewable sources—by storing energy deep into the earth.

San Miguel Electric Cooperative, a G&T based in Christine, Texas, has entered into a land-use agreement with Sage Geosystems for its 3-megawatt “Earthstore system,” which involves drilling deep into a rock formation to create an underground reservoir.

The water can be pumped into the reservoir when renewable sources such as wind or solar are at their peak, tapping excess generation. When electricity is needed on the grid—during lulls in renewable generation or other shortfalls—valves will release the pressurized water to turn turbines on the surface, providing power.

Based on the results of a pilot test project, Sage Geosystems has concluded the Earthstore system could provide long-duration, economical energy storage.

“It’s very similar to what they call pumped-hydro, where they pump up to lake. It’s working with the pressure you can build up in the earth rather than in a lake,” says Craig Courter, San Miguel Electric’s general manager/CEO. “But what’s so unique about it is you can pretty much do it anywhere. All you need is an underground rock formation.”

Sage’s pilot project indicated its Earthstore system is cost competitive with lithium batteries and could provide longer-duration storage with minimal energy loss through evaporation and leakage into rock fractures, providing dispatchable baseload power.

San Miguel Electric has the right of first refusal “to expand the project” if it’s successful, which Courter says could provide the co-op low-cost storage, important as renewables expand in Texas, a leading wind and solar energy producer.

He notes there’s an additional advantage: “Other than the equipment that’s used to drill the wall, it has a zero-carbon footprint,” Courter says. “If people want clean energy, this is about as clean as you can get.”