by Christian Roselund

California’s grid operator has reported that renewable energy sources briefly met 97.6% of demand on its grid at 15:39 on 3 April. This includes 11.51 gigawatts of large-scale solar and 5.13 gigawatts of wind, and is a new renewable energy penetration record for the California Independent System Operator (CAISO). However, an analysis of the output of various generation sources and power flows at the time show just how far California’s electricity system must go to meet state decarbonization goals.

CAISO is tasked with helping the state to achieve its target of 60% renewable electricity by 2030 and 100% carbon-free power by 2045. Energy analysts were quick to point out that reaching an instantaneous peak does not equate to meeting any given portion of daily, monthly, or annual demand with renewable energy. This and other details were explained in a twitter “thread” by Mike O’Boyle, the director of electricity policy at Energy Innovation. O’Boyle noted that at the time CAISO calculates renewables were meeting 97.6% of demand, 2.72 gigawatts of natural gas plants were still operating.

The figure of 97.6% also omits some generation, as CAISO has no visibility into “behind the meter” rooftop and other small-scale solar. Given historical deployment levels this means that around 6 gigawatts of solar was not included in CAISO’s figures. Nor was all the large-scale solar utilized; between 2 and 3 gigawatts of large-scale solar output was being curtailed between 15:00 and 16:00.

As California does not define large hydroelectric plants as renewable and did not count the output from the Diablo Canyon nuclear power plant, Energy Innovation’s O’Boyle estimates that California was meeting 107% of its demand with zero-carbon electricity sources when the record was set. CAISO’s records support this, showing that the state was exporting 3.09 gigawatts of power at 15:40.

In fact, the chief source of flexibility on 3 April was the state’s imports and exports of power, which ramped up from 3 gigawatts of exports to 8.2 gigawatts of imports at 22:00 on 3 April. California is also adding batteries very rapidly to help its vast solar resources meet evening electricity demand, but on 3 April they played a much smaller role. Despite California having an installed battery capacity of 2.73 gigawatts, the daily record shows that batteries supplied only 1.25 gigawatts at their peak output at 20:20 on 3 April – less than half the total capacity.

Regardless, California has made substantial progress in decarbonizing its power supply over the last decade. The California Energy Commission has calculated that 59% of the state’s electricity came from zero-carbon resources in 2020, including 34.5% from geothermal, small hydro, wind, and solar (collectively termed renewable energy). This is up from 41% zero carbon power, including 22% renewables, in 2013.

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Source: California ISO hits all-time peak of more than 97% renewables (CAISO)

Analysis: Did California actually hit 97% renewables in April? Yes and no (Canary Media)