What Is the Duck Curve?

Coined by CAISO in 2013, the duck curve describes what heavy solar penetration does to the load the rest of the grid must serve. At noon, solar floods the system and net demand plunges; around sunset, solar disappears just as households ramp up, forcing other resources to climb thousands of megawatts in a few hours. The steeper that evening ramp, the harder and costlier it is to serve reliably.

The duck curve is why storage and flexibility, not raw generation, dominate modern grid planning in solar-rich states. Batteries charge in the belly and discharge up the neck; demand response and time-of-use rates flatten both ends. As other states add solar, their curves are following California's — which is why battery buildouts track solar buildouts a few years behind.