The Indiana Department of Environmental Management has approved 174 emergency generators for Google’s $2 billion Fort Wayne data center, which opened in December but is undergoing continued construction. (IBJ photo/Abriana Herron)
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The power needed to operate data centers has increasingly drawn public scrutiny to the projects. But a draw from the power grid is just one of the energy issues at play.
Data centers have to keep the computer chips running even when the primary source goes dark, which makes backup generation an essential part of any data center plan. And that backup generation almost always comes from diesel fuel.
In Indiana, the state has already permitted hundreds of backup generators for a handful of data center projects, with hundreds more on the way.
And while technology companies say the generators are rarely used (they are dedicated only to infrequent power-grid emergencies and monthly testing), they’ve given data center critics concerned about noise and emissions another argument for their opposition.
Backup generators at data centers are typically allowed to operate up to 100 hours per year for non-emergencies — though there is no limit for emergencies.
As of April, the Indiana Department of Environmental Management has approved 174 emergency generators for Google’s new data center in Fort Wayne and 66 generators for its data center in Michigan City. Google also made a permit request in February for 166 emergency generators at its proposed data center in Monrovia.
Elsewhere, Amazon has been permitted to install 472 emergency generators between its two data center campuses in New Carlisle. The company plans to apply for an air permit for 766 generators at its proposed data center in Hobart, a spokesperson said.
Some smaller proposed data centers in Indianapolis are set to install dozens of diesel generators, too.
Across some projects, companies have also installed — or pledged to use — equipment that can significantly reduce emissions. For instance, the Amazon spokesperson specified that its generators are Tier-4-compliant, the category used for equipment that produces the least pollution.
Some data center operators have deployed alternative energy sources for backup power, while others are seeking regulatory frameworks that would allow them to reduce immediate data center demands when the grid comes under strain.
But demand for backup power is likely to grow, and for the time being, diesel remains the industry’s fuel of choice.
Diesel’s dominance
Almost every form of power generation has seen growth as data centers tie into the electric grid, but new backup diesel generators are almost as common as the data centers themselves.
The Better Data Center Project, a group that advocates for stronger environmental standards at data centers, released a report recently that estimated 99% of the backup capacity for data centers in Virginia comes from diesel. Virginia is the largest market for data centers in the United States.
The generators are important. When the power supply from the electric grid is interrupted, it can mean huge operational and financial losses for tech companies — and the customers they serve.
“It’s not the end of the world, but it’s really not pleasant,” said Xiaonan Lu, a Purdue University associate professor of electrical engineering technology. “So, if we do lose the power from the grid and for any reason we do not have [any alternative] resources to power the computing loads, it will go down for sure. … That can jeopardize their routine workflow.”
Heightened demand for data-center-related backup power is evident in earnings reports for manufacturers.
It was part of what drove growth during the most recent quarter for Columbus-based Cummins Inc., CEO and Chair Jennifer Rumsey said during a recent earnings call.
“Sales for the first quarter were $8.4 billion, an increase of 3% compared to the first quarter of 2025. Growth was driven primarily by higher demand in power generation markets, particularly from data centers,” Rumsey said.
Other North American manufacturing companies, including Caterpillar Inc. and Generac Holdings Inc., have noted higher demand for their generators in recent reports.
Generac, which has mostly produced backup power systems under 2 megawatts, recently released a line of diesel generators that can produce up to 3.25 megawatts marketed specifically to data centers.
Diesel generators have served as a backup power source for homes, hospitals, businesses and smaller data centers for decades, but the scale of the power demand from newer data centers is significantly larger.
“We’re talking about a single data center that could be the equivalent of the energy use of Indianapolis,” said Hoosier Environmental Council Executive Director Sam Carpenter.
Even cleaner diesel generators still produce pollution, Carpenter said.
“These generators could run for extensive periods of time, and they, too, put out lots of particulates, [sulfur oxides] and [nitrogen oxides] and things that are really going to be harmful for the health and air quality of that surrounding community,” he said.
Brad Tietz, director of state policy at the Data Center Coalition, said the industry has mostly limited the use of backup generators to power-grid emergencies such as storms in addition to required monthly testing. That means the generators produce far fewer pollutants than they’re permitted to release.
“In Virginia, the backup generators were only using 7% of their allotted emissions throughout [2023],” he said, referring to a review from the state General Assembly’s Joint Legislative Audit and Review Commission. “Understanding there are questions about the use of these backup generators, the industry does not want to use them.”
There is little public information about how often diesel generators are used to provide backup power at any given data center, but it has happened at least once in Indiana, according to public records.
The federal Energy Department issued orders allowing some utilities to request data centers turn on backup power during the January winter storm that dumped more than a foot of snow in parts of central Indiana. Amazon’s data center in New Carlisle, for example, cut its grid demand by 50 megawatts for five hours on Jan. 27 and used generators to replace it.
The specifics of that instance became public because of a cold-weather-related malfunction that Amazon had to report to the Indiana Department of Environmental Management. The incident was initially publicized by Citizens Action Coalition.
A spokesperson for the department told IBJ that no emissions violations have been observed related to backup generators at data centers in Indiana.
An Amazon spokesperson said despite the malfunction, total emissions remained below 3% of the company’s annual permitted levels.
Other options
Diesel is not the only power-source option for data centers, but other resources present challenges.
“Customers are exploring options such as natural gas generators, battery energy storage systems, turbines and other low-carbon or hybrid solutions, though diesel remains widely used today due to its fast start capability, modular reliability and on-site fuel control,” Paulette Carter, executive director of data centers at Cummins, said in a statement to IBJ.
Some data centers already use natural gas for backup power.
The complication with natural gas, though, is that it generally cannot be stored on-site, so access to a pipeline is required, said John Bangsund, director of science and technology at the Better Data Center Project.
Meanwhile, most battery storage systems are too expensive to provide a data center’s full backup power needs, Bangsund said.
“A battery system that can cover four hours of power right now costs about the same as the full diesel generator fleet that can provide basically indefinite power,” he said.
His group advocates that companies still deploy these types of batteries at data centers to offset the potential use of diesel.
Tietz, from the Data Center Coalition, said the industry is pushing for new energy solutions.
He pointed to a recent announcement by Google that it plans to build an iron-air battery system in Minnesota that could provide 100 hours of backup power.
“When you look at advanced nuclear technologies, geothermal, things like that, the industry is leaning in a number of different ways to meet the demand … to service the digital infrastructure that residents and businesses are asking for,” he said.
Technology companies are exploring other ways to address their power needs when the grid faces peak energy demands.
The Indiana Utility Regulatory Commission recently approved a demand-response program between Indiana Michigan Power Co. and Google for its Fort Wayne data center.
Under the agreement, Google would reduce or shift some data center operations to different times of the day when the local grid experiences peak demand.
These programs also have received support from some consumer and environmental groups that are often skeptical of data center projects.
Citizens Action Coalition Program Director Ben Inskeep said his group generally supports Google’s demand-response effort, though it has pushed for more information in the contract to be made public. The IURC has opened a sub-docket for the request.
“We think it would be a good example [for] other data centers to follow, not just in Indiana but around the country,” he said.
The benefit of that type of demand response, Inskeep said, is that it can prevent the need to build additional power plants and other infrastructure. He said it could also make the grid more reliable overall.
Tietz said there are limits to how much data center operators can use demand response during instances of peak demand or emergencies.
“The internet can’t just shut off,” he said.
All of these potential fixes come at a time when power-grid monitors have warned of increased strain due to higher demand, aging infrastructure and more weather-related disturbances.
Given the huge demands set for the electric grid, Lu, the Purdue electrical engineering technology professor, said the importance of backup power to data center operators will only grow.
“Backup power can release the load demand from the grid side, making it easier for the grid to handle this type of faster growth,” he said.
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