Take a big hollow sphere and sink it to help anchor an offshore wind turbine. Pump water out when you have extra wind and open a valve and let water back in, spinning a turbine connected to a generator, when it is calm. Massive engineering, but it may be a viable way to store energy.
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Whenever the wind turbines produce more power than is needed, that power would be diverted to drive a pump attached to the underwater structure, pumping seawater from a 30-meter-diameter hollow sphere. (For comparison, the tank’s diameter is about that of MIT’s Great Dome, or of the dome atop the U.S. Capitol.) Later, when power is needed, water would be allowed to flow back into the sphere through a turbine attached to a generator, and the resulting electricity sent back to shore.
One such 25-meter sphere in 400-meter-deep water could store up to 6 megawatt-hours of power, the MIT researchers have calculated; that means that 1,000 such spheres could supply as much power as a nuclear plant for several hours — enough to make them a reliable source of power. The 1,000 wind turbines that the spheres could anchor could, on average, replace a conventional on-shore coal or nuclear plant. What’s more, unlike nuclear or coal-fired plants, which take hours to ramp up, this energy source could be made available within minutes, and then taken offline just as quickly.
The system would be grid-connected, so the spheres could also be used to store energy from other sources, including solar arrays on shore, or from base-load power plants, which operate most efficiently at steady levels. This could potentially reduce reliance on peak-power plants, which typically operate less efficiently.
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There are any number of ways to store energy - the trick is finding one that is cost effective and efficient. Perhaps this one makes sense.