CAISO has long been a case study in managing an electricity grid with a high share of renewable energy. The rapid expansion of solar generation in the region has reshaped daily patterns of supply and demand, drawing attention to the “duck curve.” This concept describes net load—electricity demand minus wind and solar generation—which reflects the burden placed on conventional, flexible energy sources, such as natural gas. Named for its resemblance to a duck’s silhouette, the curve highlights the challenges introduced by abundant solar production during midday and steep ramping needs in the evening.
In recent years, continued solar buildout has deepened this pattern, transforming the duck into what now more closely resembles a canyon. The figure below illustrates CAISO’s daily net load curves over the past eight years, showing the sharp reduction in midday load.
The iconic duck curve is losing its bird-like shape as growing solar generation continues to dig deeper into net load. What began as a midday dip has driven net load below zero during certain hours, leading to a rise in curtailments, episodes of negative power prices, and increasingly steep evening ramps into peak demand. While these challenges have implications for the grid year-round, they are most acute in spring and early summer, when solar output is high but cooling demand has yet to materialize.
Solar has had a strong trajectory in CAISO over the last decade, with it being the primary driver behind the changes we’re seeing in the duck curve. Much of the attention is typically focused on utility-scale installations, but behind-the-meter (BTM) systems, such as residential and commercial rooftop installations, have seen a substantial buildout as well.
Utility-scale solar continues to rise, while BTM growth slowed in 2023 following the adoption of Net Energy Metering (NEM) 3.0, which reduced compensation for excess generation from retail rates to avoided-cost pricing. This policy shift accelerated interest in co-locating storage on BTM systems: nearly 40% of new solar applications in 2024–2025 include batteries, up from just 13% in 2023. By storing excess solar for self-consumption, customers reduce reliance on exports to the grid for cost-savings while also helping to mitigate the steep evening ramps that define the duck curve.
In CAISO, the average evening ramp can sometimes exceed 20 GW in the spring, an issue traditionally resolved by flexible natural gas plants. However, battery storage is beginning to ease this strain. By charging midday, batteries absorb low-cost solar and discharge during evening peaks, both smoothing net load and arbitraging price spreads. The figure below shows this effect in action, wherein the evening ramp is reduced by nearly 50% due to the activity of batteries.
The transformation from “duck” to “canyon” in CAISO’s net load profile is a sign of both the region’s rapid progress in clean energy development and the complexity of balancing supply and demand with increasing shares of variable resources. Utilities will have to further invest in flexible resources, demand-response mechanisms, and other innovations to ensure the transition into peak consumption remains smooth and stable. As solar adoption continues to accelerate across other ISOs, similar load profile distortions are likely to emerge.
Stay tuned for more Energy Insights as we continue to explore the ways solar and storage are affecting electricity markets across the U.S.
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