Net demand on the California ISO power system hit its lowest mark on record April 19, dropping to 5,262 MW in the early afternoon, according to grid operator data.

That beat the previous all-time low of 5,492 MW in May 2019 on CAISO's wholesale grid, which covers 80% of California and a small section of Nevada. The new record coincides with recent lower overall power demand due to the severe economic slowdown related to stay-at-home measures to slow the spread of the novel coronavirus as well as record cuts of renewable power generation to balance system supply and demand.

A measurement of power demand minus variable wind and solar resources, CAISO's daily net loads are swinging from ever lower to ever higher levels, boosting its anticipated need for flexible resources to nearly 20,000 MW in March 2021 and almost 21,000 MW in March 2022, the grid operator said in an April 14 draft report.

Depicted in the well-known "duck curve" chart, CAISO's dwindling net loads and daily generation jumps, which several times in 2019 and 2020 topped 15,000 MW over a three-hour period as the sun set, "are about four years ahead of the ISO's original estimate primarily due to under forecasting rooftop solar," according to an April 14 presentation by grid operator officials.

CAISO expects rooftop solar capacity, which reduces demand for grid power, to rise to roughly 16,000 MW by 2025 from 8,641 MW at the end of 2019.

Based on the results of CAISO's study, the grid operator will "allocate shares of the system flexible capacity needs" to utilities, community choice aggregators and other load-serving entities, according to the report.

While natural gas-fired power plants, hydropower and imports fulfill most of the state's current flexible capacity requirements, demand response and battery storage systems are emerging as additional options as California seeks to decarbonize its power sector.