Axios Pro Exclusive Content

Scoop: Sage Geosystems raising up to $20M to store energy underground

Illustration of the Earth as a battery.

Illustration: Aïda Amer/Axios

Geothermal energy and storage developer Sage Geosystems is raising a $15 million to $20 million Series A to develop underground energy storage.

Why it matters: Sage says its first project will provide up to 17 hours of energy — turning on-again/off-again renewables like solar into round-the-clock sources of power.

Catch up fast: Batteries rely on chemistry to store energy. Mechanical storage, which Sage employs, uses physical pressure instead.

  • A common example: certain types of hydropower. Water is pumped uphill to a reservoir when electricity is cheap, then released downhill through turbines when electricity is expensive or scarce.

How it works: Instead of pumping water up a mountain, Sage Geosystems will send it deep underground.

  • The Houston-based startup will drill 7,000 to 12,000 feet, then blast a fracture in rock to store water.
  • Once Sage opens valves atop the well, the fracture will push the stored water to the surface, spinning a turbine as it goes to generate electricity.
  • The storage will amount to 1.5 to 2 MW. It'll be paired with 5 MW of solar.

Be smart: It's essentially fracking — without the toxic fluids.

Details: Existing investors Nabors, the oil and gas drilling contractor, and Virya, an investment firm whose focus includes carbon capture and sequestration, have joined the Series A.

  • Sage began fundraising in January. It expects the round to close by August.
  • It's aiming to complete the demonstration project in Q3 2024.

Of note: The startup previously raised about $25 million, plus a $1 million grant from the Defense Department to study a potential 3 MW microgrid at a reserve base in Houston.

Go deeper