Curtailment is the deliberate reduction of output from a generator, most often solar or wind, because the grid cannot absorb it at that moment. In California the largest curtailments happen around midday, when solar production exceeds what load, exports, and battery charging can take.
Scale
- In spring 2026 CAISO curtailed nearly 2 gigawatts more solar over the noon peak than a year earlier, even as the state ran on more than 50 percent solar for the month of May.
- Curtailed energy is paid for and then thrown away. It is the cheapest electricity on the system, and it goes unused for lack of a place to put it.
Why it matters for parking
A car parked at a workplace, campus, or hospital garage from nine to five is sitting inside the curtailment window. Charging it then absorbs power the grid would otherwise discard, which is the case for daytime managed charging. Source: Grid Status, June 2026.