Is it fair to bill electricity separately to guests?

Separate billing is fairer than including electricity in the rental price, because then each guest pays for their own consumption instead of contributing to the behaviour of the most wasteful guest. What matters is how you do it: a clear price per kWh stated upfront, live insight into consumption and credit, and a remaining balance that simply remains the guest's property. For occasional rentals at a nominal rate or properties with little variation in consumption, separate billing is less worthwhile.