Long duration energy storage

Toronto-based Hydrostor Inc. is one of the businesses developing long-duration energy storage that has moved beyond lab scale and is now focusing on building big things. The company makes systems that store energy underground in the form of compressed air, which can be released to produce electricity for eight hours or longer.

“It’s a very simple system that just uses a hole in rock [plus] air and water,” he said. “And then the equipment is all from the oil and gas industry, so you don’t need new manufacturing or anything.”

Some background on why long-duration storage matters: The grid of the near future will require a mix of energy storage resources to fill gaps when there are lulls in generation from wind and solar. Most lithium-ion battery systems run for a maximum of four hours. Energy system planners have said the grid will also need storage options that can run six, eight, and 12 hours, and some that last as long as a day or more.

The Department of Energy has identified the need for long-duration storage as an essential part of fully decarbonizing the electricity system and, in 2021, set a goal that research, development, and investment would help to reduce the costs of the technologies by 90 percent in a decade.

A variety of companies and technologies are competing for a share of the market. This includes several types of long-duration batteries, and some resources that have been around for a while, such as pumped hydro storage at hydroelectric dams.

Hydrostor’s first large project to go online is likely going to be Silver City Energy Storage Centre in Australia, which will have the ability to discharge at 200 megawatts for up to eight hours. Construction should begin around the end of 2024, and the plant should be running by mid-2027, VanWalleghem said.


People have been talking about compressed air energy storage for decades. It’s great to hear someone is going to build one.

In much of the US we have extensive cave systems usually in limestone. They are abundant, readily available, and extensive. Why not use them?

Similarly salt domes are found in dozens of areas. They too can be huge and suitable for compressed air storage.

An excellent potential technology that has been an orphan. No one apparently has been willing to pay for test data.


Where is Bill Gates when we need him? Warren Buffett? Very nice opportunities for those willing to take the risks.

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It doesn’t sound like they would be suitable for storing water underground.


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Remember that if you have to run lines 50 miles to get to the grid, those sites aren’t worth exploring. Batteries can be sited almost anywhere. You can locate solar in lots of different places, (including right where the energy is to be used, lessening the need for more grid), you can put some other renewables in convenient places, but location is a driving force.

Gravity/water, for instance is great, except - it’s hard to find places to do it that are also convenient to the grid. Heck, it’s hard to find placers to do it, period.

Here’s a piece from today’s NYT showing changes in California energy use over 3 years. Batteries come on strong in such a short time:

Giant Batteries Are Transforming the Way the U.S. Uses Electricity

They’re delivering solar power after dark in California and helping to stabilize grids in other states. And the technology is expanding rapidly.

Gift link: Giant Batteries Are Transforming the Way the U.S. Uses Electricity - The New York Times


Re water underground.

Caves are almost always wet. Water is not a problem. Salt domes would probably require a liner. But that is ancient technology. Acids used to be stored in wooden tanks lined with lead. Today you spray on a coating.

Re Location.

Yes, all these are regional solutions. One size does not fit all. Batteries are fine but need to be huge. Geo features can be very large. Lots of capacity.

This is great. (long term storage via compressed air)
But I have to take a bit of an issue with the above that claims batteries only last for 4 hours.
What would be wrong with discharging the battery 50% as much and thus increasing the duration by 2x to get to 8 hours? Did no one think of this?

I’m pretty sure that they don’t do this because 4 hours is the sweet spot for getting the most for your money.

Also note when I saw the title I was thinking that long was far more than a day.



I title was meant to capture people’s attention. I agree the we need longer than a day storage. I think there are many people working on those concepts and they will happen. Hydrostar is starting small to tests out their concepts. If succesful results are achieved they will go to larger and longer storage.

Whenever I see articles on energy storage technologies, my first question is about the round-trip efficiency of the process.

Here is another article on this compressed air storage (CAES) technology from Hydrostor.

From the link:
Another problem with CAES is that it is much less efficient than battery storage. The round trip of compressing the air, storing it, and then using it to generate electricity is between 60 percent and 65 percent efficient.

~ ~ ~ ~ ~ ~

So, if you use 1000 kwh of electricity to compress air and store it in a cavern, you might get 650 kwh of electricity back out when you want to use it. Traditional pumped hydro and even batteries are more efficient, at around 80%.



  • Pete

You would only get half as much power for the eight hours and thus would need twice as many batteries. This would be the same as discharging the regular amount and then switching to a second tier of batteries.


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Yes, but my point was that the article title was implying some kind of breakthrough in LONG duration…as if batteries can’t store energy for more than 4 hours


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You are worried about CAES being 65% efficient. Why are you not worried about nuclear power plants and coal fired power plants being only about 33% efficient?

Because nuclear, coal and other traditional power plants all generate electricity. They convert fuel into electricity, which is the final desired product.

Batteries, pumped hydro, and this compressed air system all consume electricity. Those storage technologies consume more electricity than they produce. They consume the final product, and give you fewer kilowatt-hours in return. Because of the laws of thermodynamics, this will always be the case.

BTW, most solar panels are even less efficient than nuclear power plants, using your rules.

  • Pete