Deep in Lake Ontario is an insurance policy for Toronto’s electricity grid. On normal days, it has all the power it needs. It’s only when something goes wrong, or the grid needs an extra boost, that the city utility might call upon the facility, which stores one megawatt of power in the form of compressed air.
The new plant, which is 1.5 miles out into the lake, has been developed by a Toronto startup called Hydrostor, working with the local utility. It takes excess electricity and runs a compressor that converts the power to high-pressure air, which is then pumped underwater and into voluminous nylon bags.
“It stores power when it’s off-peak and prices [sometimes] go negative, and it sits there waiting for ice storms or super-peak days,” says CEO Curtis VanWalleghem.
Compressed air is normally stored in tanks or disused caverns. The advantage of going underwater is to equalize the pressure inside and outside the bag, creating a stable, easily managed space. Hydrostor’s idea offers an alternative to pumped hydro, when energy is in the form of water at high elevation on a mountainside, because it can be used in more locations–really, anywhere deep enough.
“It can be deployed far more places, anything coastal, or island nations and legacy mines,” VanWalleghem says. Hydrostor has another ongoing project off the coast of Aruba. Indeed, the Caribbean and Hawaii offer potential, because the water can get very deep close the shore. “The economics get better the deeper you go,” he says. “The ideal site is 200 meters [deep] within about [2.4 miles] of shore.”
Energy storage is crucial for electric grids adapting to renewable sources of power. You need storage when wind and solar are producing in abundance and the grid can’t use it all. Then you want storage when the wind goes down. Hydrostor’s storage is designed for load-balancing that takes several hours, not for the instant gratification you get with a battery.
To put down the air balloons, Hydrostor borrows a technique from the fracking industry. It drills down on-land, and then out horizontally, laying an air pipe. The method, VanWalleghem says, doesn’t disturb the fragile environment closer to the shore. “We only impact the seafloor when that pipe pops out,” he says.
Assuming the Toronto project works out, and Hydrostor can meet its target of 80% efficiency, compressed air could be a useful thing for coastal communities.