Critics of wind power keep coming back to the same old complaint: what happens when there’s no wind? A new design from researchers at MIT could finally offer a solution to this renewable energy conundrum. Engineers have conceived of an offshore wind turbine anchored by hollow concrete spheres that could also turn seawater into electricity. The turbine would allow offshore wind farm managers to store excess energy for a time when there’s no wind.

The design would use massive concrete orbs (think: the diameter of the dome on the U.S. Capitol building) to anchor floating wind turbines to the ocean floor. When it’s particularly windy and the turbines produce more power than is needed, some of the energy could be diverted to a pump that would remove the water from the hollow sphere. Then, if there comes a time when power produced by the turbines is insufficient, water would be allowed to flow back into the sphere through a turbine attached to a generator, and the resulting electricity would be 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,” reports David Chandler for PhysOrg.

According to the researchers, the trick is finding the correct concrete wall thickness to withstand the hydrostatic pressure while also providing enough ballast mass – this will depend on the strength of the concrete used. The concrete could incorporate significant amounts of fly ash from coal-fired power plants, and the spheres could double as artificial coral reefs.