Solar energy in California: batteries reduce curtailment

Solar energy in California reached an important milestone in 2025. Between January and May, curtailment decreased by 12% in relative terms (from 13% to 11.5%), despite an 18% increase in solar generation during the same period. This was only possible because batteries played a decisive role, absorbing surpluses at midday and releasing energy in the late afternoon, when prices and demand are higher.

Even so, in absolute numbers, generation cuts rose 4.1% and March registered a 28% higher peak, showing that the solution involves a combination of storage, smart grids, and active demand management. 

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The impact of batteries on solar energy in California

Batteries are changing the way the electrical system operates. During the day, they charge during peak isolation hours; at dusk, they deliver clean energy back to the system, reducing emissions and avoiding the activation of thermal power plants.

In 2024, batteries supplied, on average, 8.6% of demand between 5 pm and 9 pm and accounted for 14.7% of the load when charging between 10 am and 1 pm. Installed capacity jumped from 8 GW to 11.6 GW in 2024 and already exceeded 13 GW in April 2025, consolidating California as a global reference. This expansion ensures better utilisation of solar energy in California, reduces losses, and smooths the difference between supply and demand throughout the day.

Why does curtailment still happen?

Even with batteries, curtailment has not disappeared. It primarily occurs due to an excess of generation in relation to demand and congestion in the electrical grid. Spring and autumn are the most critical seasons, as mild weather keeps consumption low, but the sun and wind produce a lot.

Furthermore, transmission limitations prevent all generated energy from being dispatched. In 2025, the CAISO operator identified regional congestion as the primary cause of the cuts. This demonstrates that storage is essential, but it must be complemented by reinforcements to the electrical grid, more accurate forecasts, and intelligent load management to fully leverage the potential of solar energy.

Solar energy in California and the next steps

The expansion of storage has already begun to smooth the duck curve, shifting the peak consumption and stabilising prices during the most expensive hours. The next challenge is to combine more storage, regional interconnections, and demand response, so that energy is used efficiently at different times and locations.

In the coming years, battery projects are expected to continue growing, with a focus on standalone systems designed to balance the grid. If combined with investments in transmission and digitisation, this movement can further reduce curtailment, making solar energy in California increasingly competitive, predictable, and reliable for consumers and businesses.

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Source: PV Magazine