Hydrostor Is Building Underground Caverns for Affordable Compressed-Air Energy Storage

Hydrostor's Terra system for compressed-air energy storage in underground caverns
Photo:Hydrostor

Hydrostor, the Canadian company that wants to store energy as compressed air in large balloon-like bags underwater, is now turning its attention to terra firma. Specifically, the company unveiled a system to store large-scale energy in underground compressed-air caverns.

The system comes in at “half the cost of competing battery technologies, and on part with new natural gas plants,” the company claims.

The case for storing large quantities of electrical energy is getting stronger and stronger, whether to expand the use of solar and wind power or to meet surges in demand on the grid. Batteries are making headway for energy storage, but compressed-air energy storage (CAES) is a strong contender. Such systems use off-peak electricity to run compressors and store the compressed air, which can later be expanded to drive a turbine.

CAES systems have the potential to cost less and last longer once they have been built. The problem with conventional CAES is that it is expensive and requires underground geological formations to store the air.

In 2014, Hydrostor introduced plans to pack compressed air into large bags submerged underwater, with the idea of storing energy from offshore wind farms. Their latest system, called Terra, stores compressed air in an underground cavern built to operate at low and constant pressure.

The cavern has to be connected to a local water body via a pipe so that water can enter and leave the cavern as air goes out and in. The water in the shaft and cavity helps keep the air under constant pressure. To improve efficiency, Hydrostor uses an adiabatic design, in which the heat generated during compression is removed via heat exchangers and stored in a volume of water, and then, in turn, used to heat the air when it is expanded to drive the turbine.

The company’s design offers two key advantages over traditional CAES systems. It does not require special geological formations and can be built at any site close to a body of water, including urban areas. As a plus, it does not require natural gas to generate the heat for air expansion.

According to Hydrostor’s president and CEO Curtis VanWalleghem, the company is now “engaged with several utilities around the world to deploy systems rated at hundreds of megawatts.”

Hydrostor might have competition from a few other CAES startups looking to enter the market. SustainX in New Hampshire has demonstrated a full-scale system to store compressed air in pipes, while LightSail Energy plans to store air in steel tanks.

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