Just a minor point first every federal agency has a law enforcement branch (
https://en.wikipedia.org/wiki/Federa..._United_States).
But main thing is the department of Energy does not control everything that makes energy, I know this as a former worker at Grand Coulee Dam (the largest power plant in the US) it is owned by the bureau of reclamation, department of the Interior. They have Dam Police, armed security, and unarmed security, are a veterans preference job (have to by law hire a qualified veteran if available before they can even look at a non-vet). At least at Grand Coulee when I was there most likely that dam would have sided with the military.