Running On 100% Renewable

Data from the California Independent System Operator (CAISO) in late March 2024 confirmed that for 18 out of 19 consecutive days in early spring the entire electricity needs of the state were met from renewables (visual below). Renewable output exceeded demand by between 1/4th of an hour to 6 hours during the middle of the day on cool sunny spring days. The state is usually blessed with plentiful rain, ample wind, and solar energy on cool spring days when the air conditioning load is virtually non-existent.

The State of California must be powered with 50% carbon-free electricity by 2025 rising to 100% by 2045 as required by Senate Bill 100 (SB 100). The 2025 goal, while ambitious, is likely to be met. Recently the California Public Utilities Commission (CPUC) approved a plan that mandates the construction of more than 56 GW of new renewable capacity by 2035, resulting in renewable generation exceeding the state’s total demand on an annual basis, even if not at all hours.

With so much renewable generation, especially solar, CAISO is frequently overwhelmed by excess supply and must resort to curtailment due to the lack of adequate transmission capacity to export and lack of sufficient storage capacity to save it for later use. Solar oversupply in the southern part of the state averaged 1.4 GW in Jan 2024, 609 MW in Feb and 3.7 GW in the first 2 weeks of March 2024. Much of that oversupply would have normally been transmitted to northern California except that 2 south-to-north transmission lines don’t have reliable spare capacity to transmit.

The problems facing CAISO are replicated in many other parts of the world including Denmark, Spain, Portugal, and Ireland and across the US. In Texas, renewables recently reached a new peak meeting 73% of demand. Similarly, the windy Midcontinent Independent System Operator (MISO) which supplies power to 45 million people in 15 mid-western states, set a new renewable output record of 27.7 GW. Similarly, the PJM grid reported a new solar output peak of 6.6 GW, while in the New York grid behind the meter solar hit a new peak of 3.6 GW and ISONE grid posted a new behind the meter solar peak of 5.7 GW over the weekend, along with new peaks for utility scale wind and solar.

On 8 April, many parts of the US experienced a total solar eclipse as the moon covered the sun as it moved from Texas to New England (map). This reduced solar generation in its path. The grid operators were, of course, prepared to cope with the loss of solar generation as it covered solar panels across its path.

Much more needs to be done as we approach higher levels of renewable penetration including coping with the occasional solar eclipses.

This article originally appeared in the May 2024 issue of EEnergy Informer, a monthly newsletter edited by Fereidoon Sioshansi who may be reached at fpsioshansi@aol.com“