Sage Geosystems says subsurface storage and engineered geothermal approaches are near‑market; presents Texas pilot and Alaska prospects

Mike Eros, chief geoscientist for Sage Geosystems, told the Alaska House Energy Committee on Feb. 27 that his company has advanced subsurface approaches for both long‑duration energy storage and engineered geothermal, and that a 3‑megawatt demonstration in Texas has moved the technology to a high technology‑readiness level.

Sage described two related product lines: EarthStore, a subsurface pumped‑storage system that injects and later recovers high‑pressure water from engineered fractures to run surface turbines, and engineered hot‑dry‑rock geothermal systems intended for power and district heating. “Our system’s subsurface has more than 80% efficiency,” Eros said, and with surface and transmission losses included “you put a megawatt in, you get about 750 kilowatts out.”

Why it matters: the company framed its work as potentially competitive with natural gas and lithium‑ion storage for long‑duration electricity needs, and applicable at scales from hundreds of kilowatts to multiple megawatts. Sage highlighted Alaska geologic areas and the state’s rail‑belt grid as candidate zones for testing subsurface storage and geothermal because of thick sedimentary basins and heat‑flow anomalies.

Demonstration, scale and costs: Eros said Sage has raised about $55 million in private capital and spent roughly $45 million on field tests and patented drilling/fracture approaches leading to a near commercial demonstration (a 3 MW plant near San Antonio). He described a target power‑in/power‑out efficiency around 75% and said subsurface design yields a relatively small surface footprint (5–15 acres) while accessing a larger subsurface volume through directional drilling. Sage presented initial commercial targets in Texas of about $0.09 per kilowatt‑hour with potential to reach lower levels at scale; Eros said Alaska drilling and surface costs could be higher but that reuse of existing wellbores or nearby oil‑and‑gas infrastructure could materially reduce project capital expenses.

Alaska potential and regulatory notes: Eros pointed to Alaska heat‑flow maps and sedimentary basins covering parts of the Anchorage area, Fairbanks and other population centers as promising for either energy storage or geothermal district heat. He said Sage intends to operate wells well below typical groundwater zones (he cited technical depths of at least 7,000–8,000 feet) and emphasized casing, cementing and testing to protect freshwater. Lawmakers asked about rig size and logistics for remote communities; Eros said modern, more mobile drilling rigs can be brought to site seasonally and that repurposing existing wellbores would lower costs.

Use cases and partners: Eros described Department of Defense interest and feasibility studies at military posts in the U.S., a project with San Miguel Electric Cooperative in Texas and an agreement with Meta for geothermal pilot power. He said potential Alaska use cases include microgrids, repurposing stranded thermal assets and district heating for communities; he suggested utilities should evaluate levelized cost metrics when comparing alternatives.

Ending: Sage asked for data sharing and deployments to reduce project risk in Alaska and said it is prepared to engage further with state agencies, utilities and private partners on feasibility work for sites where the subsurface prospectivity and surface logistics are favorable.