In this episode, we’re diving into the world of subsurface energy storage and geothermal power with Mike Eros, Chief Geoscientist at Sage Geosystems, where he’s pioneering geo-pressured geothermal and long-duration energy storage solutions. A former ExxonMobil subsurface expert, he’s now helping reshape how we tap into and store Earth’s heat.
We explore how Mike transitioned from oil and gas into geothermal, the potential of geo-pressured systems for grid-scale power and storage, and Sage Geosystems’ groundbreaking projects reshaping the future of energy.
Episode At-a-Glance
* Storage + Geothermal: Sage merges long-duration pressure storage with geothermal heat extraction — delivering baseload + peaking power from the same well.
* From O&G to Geo: Subsurface and drilling skills transition directly into geothermal; the biggest bottleneck is industry awareness, not ability.
* EarthStore Pilot: First 3 MW project in Texas test results showing 70–75% storage efficiency with <2% fluid loss — built using off-the-shelf drilling tools.
* DoD + Meta: Early customers want resilience (military bases) and 24/7 clean power (data centers).
* Ormat Partnership: Taps into existing interconnections and Ormat’s equipment procuring capabilities — potentially reducing geothermal timelines from years to months.
* Superhot Roadmap: Drill to ~16,000 ft, then frack deep to access 300°C rock for 10× power density using mostly standard oil & gas gear.
* The Big Blockers: Organic-Rankine Cycle (ORC) turbine and broader equipment delays, interconnection queues, and lack of drilled pilots — not geology.
⏱️ Timestamps (Notes below)
[1:04] What got Mike into Geothermal? What was his career?
[6:14] How do Sage’s Pressured Geothermal Systems work?
[16:59] Why do we push the working fluid lung-like “huff-n-puff” operations in fractures?
[21:06] What are the variables affecting the economics on your projects and the efficiencies on your storage projects? How can we make geothermal scale faster?
[29:55] How does your team measure success? What are the longer term goals?
[33:57] How is your team exploring using super critical CO2 as a working fluid?
[36:15] What does it look like to build out a Sage site from ideation to creation?
[40:59] How is your team engaging with different partners to get things done?
[43:07] What are the risks and challenges your team is facing?
[45:58] How does financing these different projects look?
[49:54] How does your team work with different locales to help integrate projects with the community? What about other regulatory frameworks and environmental risks your team has to handle?
[59:31] How are the steps back in supporting certain renewables like wind and solar impacting your team?
[1:04:49] Lessons from working with San Miguel Electric Cooperative and ERCOT
[1:11:07] How is your team approaching permitting in regards to your work in Altascosa County?
[1:13:50] How has your team been approaching the grid interconnection process?
[1:15:22] Digging in on the project with the US Air Force in Starr County.
[1:19:07] How is your team developing and navigating partnerships with other military branches and the broader US military?
[1:22:31] Sage and Meta’s partnership and how the team is approaching it.
[1:25:59] Partnership with Ormat in the west.
[1:29:29] Where do you see this partnership with Ormat going?
[1:31:50] How have technological advancements in energy and drilling contributed to geothermal today?
[1:40:08] How can we get communities and the government more excited about geothermal? What can they do to help?
[1:45:18] What’s coming up for Sage?
[1:48:23] If you had a magic wand, what problem in geothermal would you solve today?
Additional Notes
* Regarding 10 to 20% dilation - As an additional note, the larger the volume put in the ground compared to the percent that is brought out/smaller volumes allows the system to stay above fracture opening pressure. This maintains sufficient presssure in the fracture to keep the system open without proppant.
* Regarding the mention of $0.065/kWh - Mike misspoke on the 10-12 cents. He meant that the costs would fall to the lower side with scale with a target of 6 to 7 cents per kWh. Additionally, for energy storage, the team is targetting Long-duration CAPEX of $2.25M/MW.
🔬 Sage’s Tech: What Makes “Geo-Pressured Geothermal” Unique?
If you’re new to Sage, their system is: part geothermal, part inverted pumped hydro.
Instead of just drilling into hot dry rock and circulating water, they:
* Drill mostly vertical wells, with a short deviation.
* Create a lung-shaped fracture network beneath the surface.
* Cycle fluid in a “huff-and-puff” pattern—injecting to build pressure, then releasing it to run a surface turbine.
Where it fits in:
* 8-12 hour duration long-term storage
* Ideal for solar-heavy regions like Texas & California, as well as Australia
* Cheaper + higher energy density than lithium-ion beyond 4 hour discharge durations
So far, this has led to:
* Round-trip storage efficiencies of ~70–75% (on par with lithium-ion and pumped hydro).
* Low fluid loss (<2%)—critical for long-term operation and environmental confidence.
This is different from some of the other well-known players as well:
* Fervo Energy: Prioritizes inter-well fracture connectivity for heat extraction (not pressure cycling).
* Quidnet: Works at shallower depths with “pancake fractures” for subsurface storage, not geothermal heat.
* Exceed GeoEnergy: Aims for closed-loop systems using CO₂ as the working fluid. (Check out our episode with the founder, Tim Tarver, here)
* Mazama Energy (and DOE superhot initiatives): Pursue ultra-deep drilling into 300+°C rock—potentially ≥10x power output. A future goal for Sage as well.
Sage, in contrast, is finding a viable bridge: using standard drilling tech and tools from oil and gas to unlock deep baseload power and grid-scale storage.
🧪 Project Highlights — More Than Just Pilot Talk
One of the most exciting things to note is how quickly Sage has moved from theory to real projects:
✅ EarthStore #1 – San Miguel Electric Coop (South Texas)
* 3 MW energy storage pilot project co-located with a coal plant with plans for 400 MW solar expansion
* Targeting Q1 2026 grid interconnection with ERCOT
* First-of-its-kind subsurface storage system using off-the-shelf turbines
* 12-month delivery from drilling to facility commissioning
With this built, Sage now has a pad that could support 10+ wells and >50 MW of long-duration storage—all without the need for mountainous terrain, vast water imoundment, and long permitting times that traditional pumped hydro requires.
🛡️ Department of Defense Partnerships
Sage has leveraged their existing work to further build projects with the DoD.
* Sage has completed geothermal feasibility study with UT Austin’s Bureau of Economic Geology (BEG) at Joint Base Ellington. (Hear more about the Bureau of Economic Geology wiht our episode with Ken Wisian (Part 1, Part 2)
* They’ve been awarded $1.9M toward a real geothermal power demonstration.
* Parallel work is now happening at Fort Bliss (Army) and Naval Air Station Corpus Christi (Navy).
* Priority: “behind-the-fence” power resilience to ensure bases can operate even if the external grid fails.
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🧠 Meta & Ormat: Strategic Scale, Not Just Experiments
Sage isn’t just proving the tech—they’re anchoring it with serious partners:
* Meta (Facebook)
* Target: 4–8 MW geothermal by 2027, with paths to scale to 150 MW and beyond.
* Location: east of the Rockies (think grid-challenged, heat-rich regions).
* Goal: 24/7 clean power for hyperscale AI data centers.
* Ormat Technologies
* Why this matters: Ormat owns dozens of operating geothermal plants already connected to the grid.
* This deal enables Sage to deploy their subsurface system into existing power sites—bypassing long lead times for interconnection and key equipment procurement.
* Mike thinks this could cut their first full-scale geothermal project timeline from several years to as little as 12–18 months.
🌱 Risk, Regulation & Water: How They’re Meeting Community Expectations
Geothermal always raises good questions about water use and induced seismicity.
Here’s how Sage is addressing those:
* Water sourcing: Using non-potable sources, including ranch and industrial water; modeling even wastewater use in future systems.
* Seismic transparency: Partnered with UT’s TexNet seismic network, run by the Bureau of Economic Geology to ensure independent monitoring.
* Fluid loss: Maintaining <2% loss is key—not just for safety, but economics based on higher system efficiencies and lower costs.
📊 Economics: What Moves the Needle
The biggest costs in geothermal are:
* Drilling and stimulation
* ORC procurement (18+ month lead times)
* Interconnection delays
But Mike made it clear:✅ Pair geothermal + storage with solar → competitive LCOE: $60–70/MWh✅ Scale from a single-well pad to multi-well → drive down cost/kW✅ Bundle into confirmed PPAs → unlock project finance instead of venture equity
🪄 Mike’s Magic Wand: More Drilling, Less Modeling
Mike’s #1 concern for geothermal right now? Funding.
“You know, if I could instantly give all of the companies that have a brilliant idea, the money that they need to test, I would do it.
There aren’t that many players on the field who actually [have] a drill ready proposal. I would do that immediately. Why beat around the bush? Let’s learn together quickly.”
What’s missing:
* Fast, catalytic funding to drill and prove commercial viability
* Public support stalled since the 1970s (For a broader history of geothermal, read more here)
* Most investors need to see more commercial successes
Bright spots:
* Rising demand from data centers and utilities for 24/7 clean power
* New Energy Secretary showing interest
* A few successful pilots could unlock a wave of private capital
🔗 Recommended Episodes
* Tim Tarver (Exceed GeoEnergy) — Advanced geothermal drilling, fracking challenges, and water reuse.
* Jen Wakeland (Beaver County, Utah) — Community engagement, rural development, and transmission planning.
* Bill Heins (Getech) — Insurance products and de-risking geothermal projects in Europe.
* Eric Bosworth (Eversource) (Part 1, Part 2) — Utility-led networked geothermal and lessons from the Framingham pilot.
* Ken Wisian (Bureau of Economic Geology, Texas) (Part 1, Part 2)— Military applications of geothermal and energy security.
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