Denholm, Paul, Matthew O’Connell, Gregory Brinkman, and Jennie Jorgenson. (2015) Overgeneration from Solar Energy in California: A Field Guide to the Duck Chart. Golden, CO: NREL.
This paper explores the California Independent System Operator’s “duck chart,” published in 2013, which shows a significant drop in midday net load as solar PV is added to the system. The authors examine how much PV might need to be curtailed if additional grid flexibility measures are not taken and how curtailment rates can be decreased by changing grid operational practices. They find that, under business-as-usual types of assumptions and corresponding levels of grid flexibility in California, solar penetrations as low as 20% of annual energy could lead to marginal curtailment rates that exceed 30%, but that by allowing (or requiring) distributed PV and storage (including new installations that are part of the California storage mandate) to provide grid services, system flexibility could be greatly enhanced.