Geothermal and energy storage company Sage Geosystems has completed a commercial pilot that indicates its new energy storage technology can provide 18 hours or more of storage capacity, and is cost-competitive with lithium-ion batteries and pumped storage hydropower.

Similar to pumped hydro in that it moves fluid through different levels, the EarthStore energy storage system operates deep inside the Earth. The technology is based on drilling a well and creating a fracture in a specific kind of rock formation. This fracture is then used as an artificial reservoir: electricity generated by a solar array, wind farm or off the grid is used to pump water into that fracture. The pressure causes the reservoir to balloon open and hold the water under pressure. When electricity demand peaks, the system’sSource: Sage GeosystemsSource: Sage Geosystems valves can be opened and the water is jettisoned back to the surface, where it passes through a turbine to generate electricity.

Field tests at an abandoned gas exploration well in Texas demonstrated production of 200 kW for over 18 hours for long-duration service and 1 MW for 30 minutes for load-following service. The EarthStore project generated electricity with Pelton turbines to power equipment on location. Subsurface system efficiencies as high as 94% were documented, with an estimated round-trip efficiency of 70% to 75%.

The company estimates that the levelized cost of storage for its technology is between 2 and 4 cents/kWh, depending on duration, compared to pumped hydro’s 6 to 15 cents/kWh, and lithium-ion batteries’ 25 to 30 cents/kWh.

The system can be paired with wind and solar to create 24x7 power, replace gas peaker plants that deliver during peak demand periods, and serve remote locations without access to a utility electric grid. The company next plans to build a power plant with this technology, comprising a single well with around 2 MW to 3 MW of capacity,

To contact the author of this article, email shimmelstein@globalspec.com