Let's look at a "worst case" on my PC. Let's say 3 attempts, 1 main step, 3 controlnet/postprocessing steps, so 64-ish seconds of generation at 300W above idle.
...That's 5 watt hours. You know, basically the same as using photoshop for a bit. Or gaming for 2 minutes on a laptop.
Datacenters are much more efficient because they batch the heck out of jobs. 60 seconds on a 700W H100 or MI300X is serving many, many generations in parallel.
Not trying to be critical or anything, I hate enshittified corpo AI, but that's more-or-less what generation looks like.