States across the country have dramatically increased their generating capacity from renewable sources, which will help them face the coming demands from summer heat. This clean power will also add a new layer of challenges during periods when the weather is extreme.

The North American Electric Reliability Corporation (NERC) is the regulatory authority that oversees the continent’s electric grid, ensuring reliability and efficiency in the areas it regulates. Its 2025 Summer Reliability Assessment (SRA), which was released in May, makes significant findings about the preparedness of the nation’s grid systems for this year’s summer weather. It also discusses the unique dynamics of clean power technology that have been added to the mix.

The SRA examines generation resource and transmission system adequacy for the upcoming four-month summer period (June through September). According to the report, an ever-expanding need for power across the nation is causing the aggregate of peak electricity demand for the authority’s 23 assessment areas to rise by over 10 gigawatts (GW) since last summer.

To put that into perspective, the number is more than double the increase for the previous year-to-year measurement from 2023 to 2024. The increase in demand is driven by economic growth as well as more demand from the industrial sector and data centers, which are expanding to accommodate the growth of artificial intelligence.

An additional 7.4 GW of generator capacity has also been retired or has otherwise become inactive for the upcoming summer. This is power that would have been generated from coal and natural gas.

On the positive side, all the areas examined in the assessment are projected to have “adequate anticipated resources for normal summer peak load conditions.” Much of the need has been addressed by the addition of new capacity from solar plus storage and wind power. The SRA projects the new solar and battery resource additions to provide over 35 GW in summer on-peak capacity. New wind resources are expected to provide an additional 5 GW on peak.

A simple calculation puts the additional 40 GW of capacity from these renewables in excess of the 17.4-GW gap caused by increased demand and retired fossil fuel generators.

However, challenges arise when the likelihood of extreme summer weather conditions is considered, along with the variable nature of the new renewable capacity. According to the SRA, temperatures in summer-peaking areas is one of the main drivers of demand. It notes that weather services expect above-average summer temperatures across much of North America this summer, as well as continued below-average precipitation in the Northwest and Midwest, which lowers the expected generation from hydropower. Supporting that projection, summer 2024 ranked in the top four hottest recorded summers, with certain areas breaking records.

The addition of further solar and wind to the power mix also makes systems more variable and less flexible because the power sources can only be harnessed when the sun shines or the wind blows. The assessment notes that solar is vulnerable on days of above-average temperature when demand persists even into the evening. The risk of supply shortfalls also increases in late summer, as the days begin to shorten and solar output diminishes earlier in the day. Solar and wind are less “dispatchable” in the traditional sense, meaning that they cannot always be relied on to ramp up generation in response to rising demand during those peak times, especially if the conditions are not conducive.

However, the SRA observes that the growth of battery energy storage systems (BESS) in recent years has markedly improved the ability to manage this variable quality of renewable generation, especially during challenging summer periods. The assessment notes that BESS resources can help meet peak demand and overcome energy shortfalls on the system “that might otherwise occur with solar down-ramps or variability.”