- 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, the company announced Tuesday.
- The company estimates that the levelized cost of storage for its technology is between two and four cents per kilowatt hour, depending on duration, compared to pumped hydro’s six to 15 cents per kWh range, and lithium-ion batteries’ 25 to 30 cents per kWh, Cindy Taff, CEO of Sage Geosystems, said.
- While the pilot tested the technology for up to 18 hours of storage, “we’re confident that it can be a weekly cycle if there’s a business need,” Taff said. “We even think it could be seasonal.”
Sage’s energy storage technology is similar to pumped hydro in that it moves fluid through different levels, according to Taff — however, it does this deep inside the Earth. The company’s model 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 of sorts.
The system can take in electricity from a solar array, wind farm, or off the grid, and use it to pump water into that fracture. The pressure causes the reservoir to balloon open and hold the water under pressure, Taff said. When electricity demand peaks, the system’s valves can be opened and the water is jettisoned back to the surface, where it passes through a turbine to generate electricity.
The technology has multiple use cases, Taff said — it can be paired with wind and solar to create 24x7 power, replace gas peaker plants that kick in during peak demand periods, and serve remote locations that don’t have access to a utility’s electric grid.
Sage’s recent pilot involved re-entering a gas exploration well in Texas, drilled by Shell in 2008, which was later plugged and abandoned. The company pumped water from a storage facility into the well over a five-week period, measuring the pressure and flow rate, which in turn determines the power output of the system, Taff said.
The company is now turning its attention to building a “power plant” with this technology, comprising a single well with around 2 to 3 MW of capacity, according to Taff. It is considering different locations, including two lignite coal mines in Texas and Louisiana respectively that are going to be installing solar energy, as well as a big wind producer in Texas that is already experiencing curtailment.
Sage’s plan is to install a first well and scale up to as many as 20 wells if the technology proves out.
“That’s why we’re strategically picking what location we’re putting it at, so that we can scale up to 50 MW,” Taff said.
The company has one technical aspect to take care of. Sage’s energy storage systems use Pelton turbines, a kind of water turbine that currently top out at a 3,000 pound-per-square-inch pressure rating, Taff said. Sage, however, will need to re-engineer it to a higher pressure rating of 3,500 PSI.
Other than that, the company will need to navigate factors like supply chain constraints, or interconnection bottle necks, that could slow down its progress.
“But by choosing these lignite coal plants or this wind installation, they’ve already got interconnection to the grid,” thereby removing one of those challenges, Taff said.