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Houston startup to build geothermal energy storage on Texas grid

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Sage Geosystems plans to build a three megawatt geothermal energy storage facility dubbed EarthStore in Texas.

A Houston-based startup plans to build what it called a “first of its kind” geothermal energy storage project in Texas.

Sage Geosystems plans to build a three-megawatt geothermal facility dubbed EarthStore, the company announced last week. The project would provide enough electricity to power 600 Texas homes during peak demand. Construction is expected to begin in the second quarter, with a targeted commission date before the end of the year, according to the statement.

The planned project would feed the grid operated by the Electric Reliability Council of Texas in its south load zone, which encompasses portions of south and central Texas. Cindy Taff, Sage Geosystems’ CEO, declined to share a more specific location for the project, citing a pending feasibility study with the local utility and a yet-to-be-submitted application to ERCOT to connect to the grid.

The project is estimated to cost $14 million, including costs for the application and for research and development, according to the company. Sage Geosystems also announced it had raised $17 million in Series A funding from investors including natural gas giant Chesapeake Energy.

Geothermal energy taps heat from below the Earth’s surface to produce electricity. Clean energy advocates have hailed the resource for its ability to provide power without climate-warming emissions and to be turned on or off at will, compared to wind and solar resources that depend on weather conditions.

No geothermal resources now provide electricity to the ERCOT grid, and no others are pending, according to ERCOT spokesperson Christy Penders.

The EarthStore project is designed to store electricity, Taff said, using subsurface heat to increase the round-trip efficiency of moving water into and out of underground fractures to generate electricity. The heat itself won’t be converted into electricity, she said.

The technology works by using fracking technology from the oil and gas industry to drill a well and an accompanying reservoir offshoot 7,000 to 12,000 feet into the earth, she said. The startup announced positive results from a pilot project demonstrating the technology in September.

When demand for electricity is low but renewable power is plentiful, the project will take electricity from the grid to pump water into the reservoir, inflating it like a balloon, Taff said. When demand is high, valves will open, and pressure will shoot water back up the well, spinning turbines that generate electricity, she said.

“Believe it or not, rock does have elasticity,” Taff said.

The startup aims to build geothermal power plants in Texas in the coming years that will tap subsurface heat specifically for generating electricity, which would require drilling wells at least 16,000 feet deep, Taff said.

Battery energy storage systems, the dominant type of energy storage, have taken off on the ERCOT grid in recent years, but these are mostly limited to short-duration uses of one to four hours. In contrast, Sage Geosystems’ EarthStore is estimated to be able to store electricity anywhere from four hours to 18 hours, Taff said.

After operating EarthStore for three months, Sage Geosystems will review the results and discuss the possibility of scaling the project up to 50 or even 200 megawatts, Taff said. The company will also discuss trying to pair with a nearby solar farm to store its electricity, she said.