The concept is pretty simple: As floating offshore wind turbines churn, they send most of the generated power to the grid. Some of the power, though, goes to pumping seawater out from 25-meter-wide hollow spheres which sit on the seafloor. As soon as the wind dies down, the pumps turn off, and the seawater rushes back into the spheres through a turbine; the water turns the turbine, which then generates electricity. The researchers calculated that one such sphere, moored in 400-meter-deep water, could store up to six megawatt-hours of power. A few hundred of those would be enough to offset an hour of energy from a typical nuclear power plant.