The late spring/early summer season in Texas can be a period of volatility when it comes to the weather. Often, the rainiest times of the year can occur in May or June. Rainfall has been occurring over various parts of the region yesterday and today, and more rain is in the forecast for the coming few days:

Figure 1 | Weather Forecast for Texas Cities

The rain and associated cloudy weather can have a meaningful impact on ERCOT's generation stack. Over the past few years, peak midday solar output has doubled or tripled (depending on which month you look at), and it's easy to find hours where solar is the largest single component of the supply stack.

Figure 2 | ERCOT Average Hourly Supply Stack, 2026 YTD

The figure above shows ERCOT's average supply stack, by hour, for 2026 so far. During non-solar hours, natural gas and wind are the two largest contributors. During solar hours, wind and natural gas are still significant, but clearly lower—and, on average, solar makes up a larger portion of the stack than anything else during the highest-output intervals in the middle of the day.

On average, the vast amounts of solar supply are great news for the grid. High demand in ERCOT often occurs when it's hot and sunny, and solar can reduce net load by 30+ GW during the midday. This results in a sharp evening net load peak, but batteries have been effective in keeping the sharpness from becoming acute.

However, the importance of solar in the supply stack makes its relative absence on cloudy days even more impactful:

Figure 3 | Solar Generation on Three Different Days in May 2026

This figure shows three example days of solar generation from this past May, with the highest value on each day labeled. On May 1^st, generation didn't really get off the ground until about HE10 and stayed below 10 GW for all but three hours of the day. On May 13^th, generation was already greater than during most hours on the 1^st by HE8 and came in over 30 GW (sometimes well over) for 9 straight hours. The 27^th was more middle-of-the-road, with a slower ramp up than on the 13^th and a lower peak, but much more total output than the 1^st.

It's important to note that the relative lack of solar generation on any given day doesn't mean that the grid will be in a state of scarcity; it also depends on the other components of the supply stack, the level of demand, outages, and so on. And, since the solar is spread out over the state, it's rare for the entire solar fleet to be blanketed with clouds simultaneously. However, this highlights the magnitude of the swings in total supply that are possible given how much solar is installed.

We track the shifting market fundamentals from day to day in ERCOT and other North American power markets. If you're interested in staying on top of these dynamics, consider subscribing to one of our Enterprise packages, or email us at [email protected] for more info.

Follow us on LinkedIn