Editor's note: SGN Managing Editor Liz Enbysk recently participated in a smart grid media tour hosted by the Ontario provincial government. With journalists from around the world, she visited utilities, smart grid companies and research labs. This is one of her reports.

By Liz Enbysk

SGN Managing Editor

If land-based wind turbines are a bird's worst nightmare, it will be interesting to see how the fish in Lake Ontario react to giant underwater "accumulators" that will store compressed air to feed back into the electric grid.

Toronto-based startup Hydrostor ran a pilot of its underwater compressed air energy storage (CAES) technology last summer and with partner Toronto Hydro will construct a 1MW, 4MWh demonstration facility about 7 kilometers from Toronto's shore later this year.

As Hydrostor President Cam Lewis explains, his company's first-of-its-kind system mechanically converts electricity from the grid to compressed air, which is captured, cooled and can be stored indefinitely in underwater accumulators. These accumulators are large, high-strength polyester bags that inflate with the air like a big balloon – no doubt producing quite an underwater show for salmon and lake inhabitants. When the grid needs the stored energy, the weight of the water pushes the air back to the surface where Hydrostor's expander/generator system sends it back. (Click to page 2 for an animated video that showcases the technology.)

The idea, Lewis says, is to transmit excess electricity at night when demand is less and reverse it when demand is high. The technology offers 70% round-trip efficiency, he says.

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Lewis sees underwater CAES as a smart choice for cities, which he says account for 75% of electricity consumed. But many find it difficult to locate generating assets close in due to NIMBYism and other issues. And that leads to higher transmission costs.

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Thirty to forty percent of cities worldwide have deep enough water nearby to accommodate underwater CAES, Newton says. And as cities grow, more accumulators can be added.

There isn't going to be a single magic bullet in energy storage, Lewis says. He believes Hydrostor's scalable, low-cost solution makes sense for urban centers and can also play a role in the growing demand for renewables and accompanying challenges of intermittency.

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"We really see our market as peak power right now," Lewis says, noting that underwater CAES is an emerging industry with research also under way in the U.S. and U.K.

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