A Data Center Ran Its Backup Generators During the July 4 Heat Wave

Ashburn, Virginia, is in the heart of America’s “data center alley.” Over the July 4 weekend, diesel generators at a Digital Realty data center switched on as temperatures spiked.

Dark smoke floated above ACC9, one of dozens of data centers clustered in Ashburn and nearby cities, according to a video and photos from July 3 seen by Business Insider. The company said it turned on generators as part of a program run by the electrical grid operator, PJM Interconnection, to reduce the load on the grid during times of peak demand.

In recent years, unprecedented volumes of cash have been pumped into America’s data center buildout and into the construction of new power plants and transmission lines. A Business Insider analysis found that 176 new data centers were permitted in 2025, which could together require enough electricity to power millions of homes.

The growing footprint of such data centers has touched off debates about their role in rising energy costs. It also has some people worried about the environmental impact of burning fossil fuels to generate backup power, particularly on days like July 3, when the high was 102 degrees in Ashburn.

“We’re talking about normalizing running our grid and protecting it with 18th-century electricity,” said Elena Schlossberg, a northern Virginia activist. “That is what diesel fuel is.”

Disaster averted

Data centers are a small minority — around 5% — of those enrolled in PJM’s demand-response programs, according to information published by the grid operator, which coordinates power generators, large loads, and utilities that supply power to roughly 20% of Americans. Demand-response programs offer power users incentive payments for agreeing to reduce the electricity they draw from the grid during peak stress times.

Across the states PJM serves, manufacturers account for 43% of demand-response capacity. In cities like Ashburn, some of the top electricity users are data centers run by companies like Amazon, Microsoft, and Equinix.

At the Digital Realty data center, a 2016 permit lists 20 Caterpillar diesel backup generators capable of producing more than 2 megawatts each. The company wouldn’t say how many were running on July 3, but said that its permits prevent it from running the generators excessively.

According to a PJM report, about 3.25 gigawatts’ worth of generation resources were run outside their limits during the weeklong heat wave that included the July 4 weekend. All in all, PJM said that demand-response programs like those the ACC9 data center was enrolled in meant that more serious steps, like an emergency order compelling the use of backup generators, weren’t required.

Bobby Chahal, a resident of nearby Leesburg, took photos of the smoke drifting from ACC9 while driving around Ashburn on July 3 and said he witnessed similar plumes rising from data centers last summer. He said this year his electricity bills have risen even though he’s not using more power.

Revenue from data centers has juiced the coffers of some of the municipalities and counties where they have broken ground. Tax collections related to a massive Meta data center in Louisiana meant huge bonuses for teachers in one part of the state. Loudoun County, where Ashburn is located, collected $875 million from data centers in its 2024 fiscal year, Business Insider previously reported, driving down each household’s share of taxes by thousands of dollars.

Still, some people who live near data centers, particularly in northern Virginia, say the noise and emissions generated by data centers have hurt their quality of life and driven down their property values.

The data-center buildout, Chahal said, “makes Ashburn look kinda industrial, kinda run-down.”