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

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

In recent years, unprecedented volumes of cash have been pumped into the construction of data centers in the United States and the construction of new power plants and transmission lines. A Business Insider analysis found that 176 new data centers would be permitted by 2025, which together could require enough electricity to power millions of homes.

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

“We’re talking about normalizing the operation of our grid and protecting it with 18th-century electricity,” said Elena Schlossberg, an activist in northern Virginia. “That’s diesel fuel.”

Disaster averted

Data centers are a small minority (about 5%) of those enrolled in PJM’s demand response programs, according to information released by the grid operator, which coordinates power generators, large loads and utilities that supply power to about 20% of Americans. Demand response programs offer customers incentive payments for agreeing to reduce the electricity they draw from the grid during stressful peak hours.

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

At Digital Realty’s data center, a 2016 permit lists 20 Caterpillar diesel backup generators capable of producing more than 2 megawatts each. The company did not say how many were operating as of July 3, but said its permits prevent it from over-running the generators.

According to a PJM report, about 3.25 gigawatts of generating resources ran off limits during the week-long heat wave that included the July 4 weekend. Still, PJM said demand response programs like those the ACC9 data center was enrolled in meant more serious steps, such as an emergency order mandating the use of backup generators, were not required.

Bobby Chahal, a resident of nearby Leesburg, took photographs of smoke billowing from ACC9 as he drove through Ashburn on July 3 and said he witnessed similar plumes rising from data centers last summer. He said this year his electricity bills have increased even though he is not using more energy.

Income from data centers has swelled the coffers of some of the municipalities and counties where construction has begun. Tax revenues related to a huge metadata 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, reducing each household’s tax share 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 reduced their property values.

The data center construction, Chahal said, “makes Ashburn look a little industrial, a little run down.”