In sunny California, solar panels are ubiquitous, adorning both desert landscapes in the Central Valley and urban rooftops in Los Angeles. With nearly 47 gigawatts of solar power installed, the state boasts the capacity to power 13.9 million homes, contributing over a quarter of its electricity supply.
However, California now faces a perplexing issue: an oversupply of solar power leading to negative electricity prices on sunny spring days with lower demand. This phenomenon, known as curtailment, results in wasted gigawatts of solar energy.
To address this challenge, California has scaled back incentives for rooftop solar and slowed installation rates. The state’s response raises concerns about the future development of solar energy in a region committed to renewable energy goals. Moreover, as other states embrace solar power, they may encounter similar issues.
Michelle Davis, head of global solar at Wood Mackenzie Power and Renewables, acknowledges the challenges faced by grid operators, stating, “These are not insurmountable challenges, but they are challenges that a lot of grid operators have never had to deal with.”
The root of the issue lies in the “duck curve” phenomenon identified by California’s grid operator, CAISO, over 15 years ago. This curve depicts a significant drop in electricity demand during midday hours when solar power generation peaks, followed by a surge in demand as the sun sets.
In recent years, California has witnessed a deepening of the duck curve, leading to substantial solar curtailment. In 2022 alone, the state wasted 2.4 million megawatt-hours of electricity, with solar accounting for 95% of the discarded energy.
Clyde Loutan, principal for renewable energy integration at CAISO, attributes the rapid rise of residential solar installations to the unexpected challenge. However, he emphasizes that the state’s grid was not fully prepared for this influx.
While curtailing solar power is technically straightforward, it raises electricity prices and undermines the economic viability of rooftop solar. Changes to California’s net-metering system, which compensates solar panel owners for excess energy fed into the grid, have further complicated matters. The backlash from consumers and solar companies has prompted calls for policy reversal.
Despite the setbacks, experts believe that California’s experience can serve as a valuable lesson for other states navigating the transition to renewables. Solutions such as energy storage, additional transmission lines, and regional power sales are being explored to manage excess solar energy and alleviate grid strain.
Paul Denholm, senior research fellow at the National Renewable Energy Laboratory, underscores the importance of proactive measures, stating, “There are fundamental limits to how much solar we can put on the grid before you start needing a lot of storage. You can’t just sit around and do nothing.”