How to sell electricity in SAP?

I'm implementing SD module for an electricity company A, which has two customers one is state owned company B and the other is a school.

Company A produces electricity with Solar energy and signs a contract with company B, the contract contains price etc, but no exact amount or volume of electricity. Company B will sell electricity to all society.

As you know, electricity is a very special material, no stock, the first thing I need to consider is that what kind of material type to be used.

what about service material NLAG (non-stock)? or PIPE?

if we treat electricity as service material, once sales order is created, we can bill it immediately with no delivery required.

what are your ideas? what else should I consider in selling electricity in SAP SD?

Thank you very much