Curtailment

Curtailment is the deliberate reduction of a generator's output below what it could otherwise produce, most often applied to wind and solar plants when a grid has more low-cost renewable supply available than it can use or move at that moment. California's grid operator, the CAISO, describes the mechanism plainly: its market automatically reduces, or curtails, renewable generation to match supply with demand, a routine and growing feature of operating a grid with a deep midday solar surplus, the same surplus behind the duck curve.