Curtailment

Switching off or reducing solar or wind output that could have been generated, because demand or grid capacity is insufficient.

A power grid must balance generation and consumption at every moment. When sunny, windy hours produce more than is needed, the surplus has nowhere to go and output must be cut. A 2016 review by Lori Bird and colleagues traced how this discarded electricity has grown as countries add renewables^[1].

In Japan, curtailment of solar is frequent in Kyushu and elsewhere. Storing that otherwise wasted electricity cheaply and shifting it to hours of shortage is a major reason for building more batteries.