Project Management Institute

Underwater energy

a Canadian project team looks at giant underwater balloons to store excess power from the grid


About 60 meters (197 feet) below the surface of Lake Ontario, Canada, six giant balloons are storing energy—and potentially reducing Toronto's reliance on fossil fuels.

The balloon project sponsored by Canadian energy startup Hydrostor Inc. converts electrical energy into compressed air and sends it through a 2.5-kilometer (1.6-mile) pipe underwater to the coated-nylon balloons. The six three-story balloons, anchored by 30 straps apiece, together take up the equivalent of a basketball court.

Hydrostor is partnering with Toronto Hydro, Canada's largest energy distribution company, on the two-year pilot project to use the balloons to store excess energy generated by Toronto's grid. The project began in November 2015. By potentially saving solar- or wind-generated power, they could offset dips in renewable power availability during cloudy or non-windy days, which currently drives reliance on coal and gas power.

“Most of the world is saying we have to get off fossil fuels,” Hydrostor CEO Curtis VanWalleghem told the Toronto Star in late 2015. “To do that, you need lots of energy storage.”

When energy demand increases, the system uses Lake Ontario's natural pressure to push air out of the balloons to a turbine, where the electricity is regenerated and sent back to Toronto's grid.

Hydrostor executives say they see potential to scale up the project concept to coastal cities such as Los Angeles or Tokyo. Another potential project plan: repurpose abandoned mines by putting the balloons at the bottom and filling the mines with water. —Brigid Sweeney


The three-story balloons together take up the equivalent of a basketball court.

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