Winter Is the New Summer: The Seasonal Grid Stress Ahead

Understanding the Emerging Seasonal Shift in Net Load

Seasonal net electricity load across the U.S. is undergoing a fundamental shift from peaking in summer to increasingly peaking in winter. This change is driven by two powerful trends: the rapid expansion of solar generation, which depresses daytime load in the summer, and the accelerating growth of electricity demand from data centers, which is largely insensitive to seasons. Our energy planning frameworks must take notice and catch up. 

This notion of net electricity load refers to the total electricity demand minus renewable generation. The remaining net load represents the portion that must derive from other resources, including natural gas, nuclear, and storage. As explained in the video below, net load is central to both system economics and reliability planning.

As mentioned, the emerging shift is driven by the interaction of two major forces:

1. Solar generation is highly seasonal. In recent years, the United States has installed unprecedented amounts of solar generation. In 2025, 81% of all utility-scale capacity additions were either solar or short-duration battery systems. When combined with behind-the-meter solar and batteries—resources that have a similar profile—the system experiences a strong downward pull on net load during sunny summer days.
2. Data center demand is large, persistent, and largely temperature-independent. Data center capacity in our modeling grows 100 GW from today to 2040.  

As a result, the system experiences:

• Deep solar-driven reductions in summer daytime net load, but
• High and steady demand during winter periods when solar contributes the least.

The outcome is a seasonal inversion: the most challenging period for system reliability is migrating from the hottest days of summer to the coldest days of winter. The influx of midday solar generation pushes net load to very low levels during daylight hours, followed by a steep increase as the sun sets. This phenomenon, known as the “duck curve,” has already shifted many regions’ daily net-load peaks into the early evening. Looking forward, the shift is not only intraday but increasingly seasonal.

Tracking the Seasonal Transition with Ensemble Analysis

Using Evolved Energy Research’s RIO model, we ran an Ensemble of 100 scenarios under the OBBBA and examined when different U.S. regions are likely to evolve from summer-peaking net load to dual-peaking systems, and ultimately to strongly winter-peaking net load.

The map below illustrates this transition using the ratio of winter net-load peak to summer net-load peak.

• Red regions illustrate summer net-peaking conditions.
• Blue regions correspond to winter net-peaking conditions.
• Intermediate colors represent systems in the midst of a dual-peak regime.

As can be explored in the interactive map, Alaska is the only state in 2025 with the deep blue markings of winter-peaking net load, with some blue visible in the Northwest and the Southeast (due to the prevalence of electric heating in both regions). However, by 2040, all but a handful of states in the Southwest transition to winter net-peaking.

Implications for Reliability and Resource Planning

Addressing a winter net-peaking system requires fundamentally different planning. Summer net peaks have historically been dominated by short-duration, high-intensity events linked to air conditioning. Winter reliability challenges, by contrast, often involve sustained periods of low renewable production coupled with high, steady demand.

Managing these conditions will require:

• New planning frameworks that account for prolonged low-renewables conditions and can accommodate all-hours reliability challenges.
• Resources without duration constraints such as longer-duration storage technologies, thermal resources that provide sustained output during extended low-renewable periods, and, in some cases, backup generators at data centers that can operate for effectively unlimited runtimes.
• Sustained demand flexibility for data centers and other large industrial loads that may be called on to reduce load for sustained periods. While data center operators frequently discuss load flexibility, far less attention has been paid to the duration over which that flexibility can meaningfully contribute. Short-duration adjustments may help smooth summer net-peaks, but they provide limited benefit during extended winter reliability events.