A rule that could change how temporary power at data centers is permitted is now at the White House. The Environmental Defense Fund (EDF) said on 20 October that the US EPA has sent its proposed Nonroad Combustion Turbines Rule to final review. As EDF describes it, the rule would take certain combustion turbines out of the Clean Air Act programs written for industrial plants and regulate them as mobile sources, the way vehicles and off-road machinery are treated. We have not seen the proposal text, so what follows is EDF's reading, and EDF opposes the rule.
What a stationary turbine goes through today
According to EDF, gas turbines that power data centers generally need a Title V operating permit and a New Source Review permit before construction, and they have to meet NOx limits under Section 111 of the Clean Air Act, which EPA revised in January. Those permits bring pollution controls, a check against local air quality standards, public notice and comment, and emissions monitoring. EDF's argument is that a nonroad classification would remove most of that, including the local review and the public involvement.
What January already changed
The turbine standard published on 15 January had already eased things in two ways, as the law firm Clark Hill summarizes it. A temporary subcategory covers turbines up to 850 MMBtu per hour that run for less than 24 months and carry a less demanding NOx standard, and certain low-use turbines are exempt from Title V. A temporary unit cannot simply be swapped for another temporary unit to stay out of permitting.
The same rule contains a conditional exclusion. Temporary turbines drop out of the definition of a stationary turbine altogether if they qualify as nonroad engines and are certified to mobile-source standards, but only once EPA has adopted those standards for portable turbines. EDF presents the proposal now in review as the follow-up. It also notes that an industry group, the Coalition of Mobile Electric Turbine Users, petitioned EPA last year to have trailer-mounted turbines on gas or distillate fuel classed as nonroad engines.
The one-year limit nobody can easily check
A nonroad engine may not stay at one location for more than a year. EDF's worry is enforcement: without a permit, regulators often have no practical way to confirm it. The group adds that a cluster of portable turbines can emit about as much as one large power plant, and cites figures from the Southern Environmental Law Center for a 27-turbine site in Mississippi, with potential emissions of 1,700 tons of NOx a year. EDF expects the rule to reach beyond data centers, to oil and gas facilities too.
Where engines and generators come in
The rule under review is about turbines. Engine sets are not named in EDF's release, though a Frantz Ward note from May says EPA has been looking at lighter permitting for temporary power in general, turbines and diesel generators alike, during data center construction and early operation. The same note reminds readers that regulators may add up a group of backup generators by ownership, proximity and how dependent they are on each other, and that many developers still design to stay below the major-source line. States are not all moving the same way: Virginia has written Tier 4 into its rule for new data center generators (our report).
For anyone planning bridging power before a grid connection arrives, the question "is this unit temporary in the legal sense?" now comes before "which unit?". Put it to the permit office in writing, with the expected years on site. And do not price a project on an exemption that has not been published yet.
Sources: Environmental Defense Fund, Clark Hill, Frantz Ward