Using real-world data from the state’s main grid, the study counters [pdf] concerns that grids dominated by solar and wind energy will lead to costly, unstable electricity.
California’s increasing capacity in solar photovoltaics, wind, and battery storage—alongside reductions in demand from installations like household solar panels—enabled the state to meet 100% of grid demand for parts of 98 days over a 116-day period from late winter to early summer. These periods—when wind, water, and solar (WWS) sources met demand—ranged from a few minutes to more than 10 hours per day, with no blackouts reported.
The study focused on WWS, but other energy sources were also generating electricity during those times.
Excess power was exported to other states or stored in batteries for later use, while also shifted excess solar for later use, supplying up to around 12 % of nighttime demand.
In some cases, excess generation was curtailed, meaning it wasn’t used. The study suggests future grids can use curtailed electricity for other applications like district heating, high-temperature industrial process heat stored in firebricks, or green hydrogen production for ammonia and steel plants.
An uptick in behind-the-metre solar resources helped lower overall demand, say the researchers, noting that in 2024, these sources met 12.9% of California’s electricity retail sales from October through September. Moreover, recent state-level restrictions have held back rooftop solar installations, meaning their contribution to lowering demand could have been even greater.
The study also shows that California’s renewable energy sources increased considerably in 2024 compared to the previous year. Nameplate capacities of utility-scale solar, wind, and batteries were about 18%, 4%, and 73.3% higher, respectively. WWS reached peak generation on May 5, 2024 at 162.3% of demand, compared to a 2023 peak of 129%.
The overall effect contributed to an estimated 40% drop in gas use.
The study also addresses concerns that large-scale renewables deployment will raise electricity prices, finding that an increase in California’s rates was caused by other factors:
“Aside from the high cost of fossil gas in California, a big factor is wildfires,” the researchers write. “Utilities have passed on to customers the cost of wildfires caused by transmission line sparks, the cost of undergrounding transmission lines to reduce such fires, and other wildfire-related mitigation costs.”
Data from other studies indicates that WWS actually tend to lower prices. Of 12 U.S. states with the highest WWS supply as a percent of demand, six were among the 10 states with the lowest residential electricity prices in March 2024, write the authors, while 10 were among the 20 lowest. Only two, California and Maine, recorded higher prices.
