California's renewable fleet just wrapped up its toughest semester on record. Through the spring, solar output routinely outran the grid's ability to absorb it, and curtailment volumes exploded, averaging roughly 48,700 MWh a day in April and 46,700 MWh in May. That's about double March's already-elevated pace and nearly six times what the market saw back in February. Every extra megawatt of spilled solar and wind represents clean power that got built, bid in, and then turned away because there was simply nowhere for it to go in the middle of the day. For a stretch there, it looked like the new normal, a structural mismatch between how much solar had come online and how much midday load was around to use it.

Then summer showed up. As real heat settled over the CAISO footprint in early July, demand climbed and curtailment fell off a cliff, down to about 8,500 MWh a day through the first ten days of the month, the lowest mark since January. The most telling part is the year-over-year comparison: this July's pace is tracking almost where 2025 sat in the same window. In other words, spring 2026 was the outlier, not summer. The grid didn't suddenly get better at soaking up renewables, and no new transmission or storage magically appeared overnight. There was just more solar on the system this year, and once the heat arrived to lift demand, the grid finally had somewhere to put all that extra power.

Figure 1 | Average Daily Solar + Wind Curtailment by Month, 2025 vs. 2026

The July 4–10 heat event told the story in real time, and it's worth looking at which resources were actually doing the work. During the critical evening ramp, the late-afternoon hours when solar fades but demand stays high, thermal generation more than doubled across the week, and batteries ran hard every single night to help cover the gap. But here's the key: solar and wind never had to step aside to make room. Solar kept pouring out through midday and still contributed meaningfully into the evening. Rather than curtailing renewables to balance the system, the grid needed everything running at once just to keep up with load, which is the exact opposite of a curtailment problem. The day-ahead market noticed too, re-pricing both NP15 and SP15 well above their month-to-date averages. And notably, that price move was driven by physical fundamentals, gas burn and heat rates climbing as thermal picked up a bigger share of the stack, not by any shift in carbon allowance costs, which barely budged all week.

Figure 2 | CAISO Evening Ramp Generation Mix by Fuel, July 4 to July 10, 2026

Of course, summer break doesn't last forever. Just like the school year, curtailment will be back on the fall schedule as the days shorten, cooling demand fades, and all that midday solar once again has nowhere to go. It's a seasonal rhythm this market is going to keep living with as the solar fleet grows. For now, though, the story has flipped from spilled megawatts to how tightly the next heat wave will price the ramp, and with another round of extreme heat already bearing down on Southern California, that next test is here. Want the full picture, with the figures, price tables, and the month-by-month curtailment breakdown? Check out the complete article, "Summer Break is Here."

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