Exclusive: One startup's quest to store electricity in the ocean | TechCrunch

"When Manuele Aufiero was a child, his parents would take him hiking along a reservoir in northern Italy. It wasn't a typical reservoir, though. This one drained and refilled constantly, with pumps raising the water level when electricity was cheap. When nearby cities needed electricity, the pumps would reverse, turning into generators as the water drained out of the reservoir."

"The technology, known as pumped-storage hydropower, or pumped hydro for short, has been around for over a century. Such facilities are some of the biggest "batteries" humans have ever built. Globally, pumped hydro reservoirs store 8,500 gigawatt-hours of electricity, according to the International Energy Agency. Pumped hydro can generate electricity for hours on end, and the power plants have grown in importance as intermittent energy sources like wind and solar have become more widespread."

Reservoirs that pump water uphill when electricity is cheap and release it to generate power have existed for over a century, storing about 8,500 gigawatt-hours globally. Such pumped-storage hydropower supplies hours-long electricity and supports variable wind and solar, but suitable topography is scarce. Sizable Energy adapts pumped hydro to the ocean by using two sealed flexible reservoirs—one floating near the surface and one on the seabed—linked by a plastic tube and turbines. Investors led by Playground Global committed $8 million to the startup. The system pumps super-salty seawater to the upper reservoir when prices are low and releases it to drive turbines when power is needed.

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