Regarding reimbursment

no. your intention is wrong.

reimbursement of amount is not an income.

as per your case ititially you are paying electricity bill onbehalf of your tenant. i.e. adv given to tenant.

when you are collecting money from your tenant. i.e. collection of advance money given to your tenent.

so reimbursed amount can't be considered as income.

NOte: if your expenditure is reimbursed by some body is income.