xAI runs 35 gas turbines at Colossus against a permit for 15

xAI's Colossus data centre in South Memphis has drawn part of its primary power from on-site methane gas turbines since it opened in 2024. In mid-2025 the Shelby County Health Department issued a permit covering 15 turbines, which xAI described as backup power.

Aerial and satellite imagery gathered by the Southern Environmental Law Center showed far more units on site — 35 at one point, with 24 observed operating in July. SELC's modelling puts the turbines' nitrogen-oxide output above 2,000 tons a year, which would make xAI the largest industrial source of the smog-forming pollutant in Memphis.

The NAACP and Young, Gifted and Green appealed the permit to the Memphis and Shelby County Air Pollution Control Board, arguing the turbines were wrongly treated as exempt "nonroad engines" under the Clean Air Act. SELC, Earthjustice and the NAACP also sent xAI a notice of intent to sue. xAI called the allegations "baseless and politically driven".

Why it matters for the index: on-site fossil generation is the single largest driver of a low carbon score, and contested permitting weighs on the conduct pillar.