The Rise of the Duck Curve in ERCOT: A Shift in Net Demand Peak and the Future of Solar Power Integration
As solar energy continues to grow in Texas, ERCOT’s net demand patterns are shifting. One key change is the rise of a phenomenon called the “duck curve,” driven by increasing solar generation and its impact on demand. During sunny afternoons, net demand drops sharply as solar power reduces the need for other sources. But in the evening, when solar fades, demand spikes again.
This pattern is reshaping Texas’ energy grid. But the real challenge comes after sunset, when demand often remains high, but solar power disappears. On hot, still nights, wind generation can also be low, leaving the grid vulnerable with little renewable energy available when it’s needed most. That’s why understanding not just how much demand there is, but when it occurs — and how much power is still needed after renewables decline — has never been more important.
ERCOT's Shift to Later Net Demand Peak
For years, ERCOT’s net demand peak occurred around 5:00 PM during the summer months, driven by the combination of rising temperatures and increased electricity use in the late afternoon. However, as solar generation grew, a notable shift began to emerge: the net demand peak is now moving later into the evening. This shift can be attributed to solar power covering a larger portion of daytime electricity use, followed by an increase in demand as the sun sets and people continue using electricity.
This evolving pattern first became noticeable around 2021, when a secondary peak began to emerge in the evening. By 2022, this shift was more pronounced, with evening net demand rising significantly after the sun sets around 8:30 PM in the summer. This trend has continued and is now firmly established, with net demand in ERCOT consistently occurring closer to 9:00 PM rather than the traditional 5:00 PM.
Is CAISO's Duck Curve ERCOT's Future?
With this shift in net demand, ERCOT's evolving load profile is starting to resemble the famous "duck curve" seen in CAISO. In the duck curve, solar generation peaks during the day, but as the sun sets, there's a steep drop in solar output, leading to a sharp increase in demand in the evening hours.
Could ERCOT’s future soon look like CAISO’s duck curve? As solar energy continues to play a larger role in Texas’ grid, ERCOT is likely to see more pronounced evening peaks. But unlike CAISO’s steadier trajectory, ERCOT’s net demand has surged more rapidly in recent years — growing over 300% since 2021 compared to CAISO’s 67% — highlighting a much faster pace of change in Texas.
That said, the duck curve is taking a different shape in each region. CAISO’s curve is clearly defined, with a deep mid-day dip and steep evening ramp. This is largely the result of high solar penetration. In contrast, ERCOT’s curve is just beginning to form. Despite larger and faster solar growth, Texas hasn’t yet developed the same mid-day dip, likely due to different load patterns and system characteristics.
One big reason CAISO’s curve is now more manageable is the rise of battery storage. In recent summers, California has avoided grid emergencies and even skipped Flex Alerts altogether — thanks in part to batteries that soak up solar energy during the day and discharge in the evening when the sun sets. This shift has made a noticeable impact on reliability.
For ERCOT, this may be a signal of what is needed next. While Texas is rapidly adding batteries and expanding demand response programs, building out these flexible resources sooner rather than later could help the grid avoid the reliability challenges California faced in earlier years. As ERCOT’s evening ramp becomes more pronounced, the tools that helped stabilize CAISO, like storage and demand-side flexibility, could prove just as essential in Texas.
This evolving load shape isn’t limited to California and Texas. In 2025, MISO, the grid operator across much of the Midwest, began to show early signs of its own duck curve, with mid-day demand dips emerging as solar capacity grows. By learning from the paths taken by CAISO and ERCOT, MISO has a timely opportunity to get ahead of the curve — literally — by investing in battery storage and flexible resources now to manage evening ramps and maintain reliability as solar continues to scale.
What This Means for Forecasters
Net Demand Shift: ERCOT's net demand peak has moved from 5 PM to 9 PM during key summer months, driven by solar growth.
Duck Curve: ERCOT’s load shape is evolving similarly to CAISO’s "duck curve," though with unique Texas-specific characteristics.
Forecasting Matters: Accurate net demand forecasting is critical for grid reliability, especially during the vulnerable evening ramp hours.
For forecasters, this evolving pattern changes everything. As renewables fade in the evening, the timing and accuracy of net demand forecasts become critical for managing risk. These forecasts help grid operators and market participants anticipate late-day peaks, deploy resources more effectively, and make smarter operational decisions.
By shifting focus from total demand to net demand, we’re not just improving predictions — we’re helping people stay ahead of the curve, make better choices, and keep the grid resilient in the face of rapid change.
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