Line losses? Light? Oxydation?
Oops - forgot generation inefficiencies.
Line losses are from the resistance. It creates heat. What would be losses for a motor turning are contributions to heating in this case.
Light - In a heating element, this nearly all infrared, contributing to the heat. There is some minimal visible light, but not a reasonably measured amount in terms of energy loss.
Oxidation? Electrons forming chemical bonds come from the atoms being bonded, not outside sources like the power supply. Even this is extremely very small, to the point of not being measurable amounts of energy or the heating element would be gone nearly immediately.