Seven hundred and twenty-six megawatts of diesel generation is more than many power stations have, and at Digital Realty's new campus in Charlotte, North Carolina, it is only the standby plant. WFAE, the city's public radio station, reported on 11 November that a proposed Mecklenburg County air quality permit would allow the company to run 242 diesel generators at its hyperscale data center on Moores Chapel Road when the mains supply fails. The permit would allow more than 100 tons of air pollutants a year, among them smog-forming emissions and carbon monoxide. The regulators have not decided yet, and according to WFAE the public comment window closes on Tuesday.
400 MW Of IT Load, 726 MW Of Standby
The Charlotte Observer described the project in August: a 156-acre site in the southwest of the city with two buildings of 3 million square feet in total, laid out for up to 400 MW of IT capacity, which would make it one of the largest data centers in North Carolina. Digital Realty is paying for a new substation that Duke Energy will own, build and operate; permit records put the spending on that structure at upwards of $53.5 million.
Divide the generator total by the number of sets and the average is 3 MW per machine. Neither report explains the distance between 400 MW of IT load and 726 MW of generators, but it is the normal picture: the standby plant has to carry cooling and building services as well as the servers, and it is built with spare units so that a set that fails to start does not cost a data hall.
Construction is well under way. TarSignal, which reads local permit records, counted $488.7 million of declared building and upfit costs at the campus between March and September, a shell permit for a building of 1.29 million square feet issued on 29 May, and two dozen electrical permits covering switchgear, generators, UPS and the medium-voltage feeders from the substation.
Approved Before The Moratorium
Digital Realty bought the land two years ago, and Charlotte City Council rezoned it in May 2025, with little fanfare as WFAE puts it. On 8 June 2026 the council voted unanimously for a 150-day moratorium on new data centers, running to 5 November, but it does not reach projects that were already approved, and this is one of them.
The permit is not a first for the state. In August the North Carolina Division of Air Quality issued one for 588 backup generators at Amazon's data center in Richmond County, TarSignal reports, and the state's environment secretary said then that the division's legal authority in reviewing such projects is limited.
Tons A Year Become Running Hours
WFAE's report does not name the engine make, the emissions tier or a limit on running hours, and those are the details that decide how such a permit works in daily operation. An annual tonnage cap is in effect a budget of engine hours. With 242 sets the routine test programme uses a good part of it before any real outage happens, so somebody has to plan which sets run, for how long and at what load, and keep the records to prove it.
Whether the regulator accepts standard standby engines or asks for exhaust aftertreatment is worth knowing before the generators are ordered. Aftertreatment changes the package around the engine, from the exhaust run and the reagent supply to the enclosure and the cooling air path, and it is far easier to design in than to add. Virginia has already gone that way, as we described in our item on its generator rule; the application is covered on our data centers page.
Sources: WFAE, The Charlotte Observer (via AOL), TarSignal
