Perhaps you could install this Emporia Smart Home Energy Monitor with 8 50A Circuit Level Sensors on (only) the circuits that go to the rental and then bill the tenant for the power used.

Or you could install a subpanel for the circuits that go to the rental unit and then use a submeter to determine how much energy is used to bill the tenant.

-- amateur

Seems pretty straight forward. I'd just estimate the amount of electricity they'll use and include it in the rent. Will you be able to easily access it, is the question.

IMO just add the utilities to the monthly rent price most tenants love it when it is included but you need to be able to always access the panel so that needs to be addressed .