Geothermal energy storage of 18 hours or more

Dive Brief:

  • 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.”

I was curious how they could possibly store energy that way. From the linked article:

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.

That is certainly geo-something, but despite the headline it is not geothermal.


A basic principle of hydraulics is that water does not compress. Storing pressurized water underground has to mean something moves and then rebounds when pressure is released.

There must be lots of potential for surprises. How many cycles before it fails. Or is it that the water is compressing under ground air chambers.

Interesting technology but i think i will not be first to invest. Need more data.


They probably call it geopumpedhydropressure.

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This is textbook fracking. Luckily, we’ve rebranded it as green, so it’s now fine.

(it was fine before, too, BTW)

There are also reports of using underground storage of compressed air. Yes, fracking makes sense. But why water instead of air?

Compressed air is a bomb without a fuse.

When water “pops”, it looks like an oil well, not a bomb.

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But without the toxics used in fracking for O&G!

“Toxics in fracking”

They routinely inject particulates to maintain space between the rocks. The “toxics” are probably dispersants to help suspend those particles. Toxics might be extremist language. They need not be a major concern but probably are present in fracking for energy storage.

Different chemicals are added for different purposes, based on the rock type and other specifics of a fracking site. Acids, for example, are used to dissolve minerals to help fossil fuels flow more easily; biocides eliminate bacteria; gelling agents help carry proppants into fractures; and corrosion inhibitors prevent steel parts of the well from being damaged by fracking fluid. The EPA identified 1,084 different chemicals reported as used in fracking formulas between 2005 and 2013. Common ingredients include methanol, ethylene glycol, and propargyl alcohol. Those chemicals, along with many others used in fracking fluid, are considered hazardous to human health. Meanwhile, and perhaps more disconcertingly, the potential human health impacts of the majority of chemicals used in fracking formulas are simply unknown.

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Yes, and you can drown in water. It too is hazardous to your health.

Methanol and ethylene glycol are known to be toxic if you drink them. But in small amounts they are unlikely to cause problems.

I’d be surprised if “propargyl alcohol” is accurate. Propylene glycol is more likely. It is non-toxic and usually considered suitable in foods.

The fact that aspartame is a methyl ester that can hydrolyze to methanol is the basis of some claims against it.

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I do not think the system described in the OP wants to have toxic chemicals in the power generation machinery.

“Toxic chemicals” is a very broad category. At some level all are.

I’m sure the people involved with do the best they can to minimize use of toxics.