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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. //
Unlike some other long-duration storage companies, Hydrostor has proven its technology. The company has operated a small, 1.75-megawatt plant in Goderich, Ontario, since 2019, which can run for about six hours at a time. Compressed-air storage existed before Hydrostor—plants in Germany and Alabama have been around for decades and use variations on this approach.
Hydrostor’s system uses a supersize air compressor that ideally would run on renewable electricity. The system draws air from the environment, compressing it and moving it through a pipe into a cavern more than 1,000 feet underground. The process of compressing the air produces heat, and the system extracts heat from the air and stores it above ground for reuse. As the air goes underground, it displaces water from the cavern up a shaft into a reservoir.
When it’s time to discharge energy, the system releases water into the cavern, forcing the air to the surface. The air then mixes with heat that the plant stored when the air was compressing, and this hot, dense air passes through a turbine to make electricity.