Each corporation shall be operated without profit to its members, but the rates, fees, rents, or other charges, for electric energy, and any other facilities, supplies, equipment, appliances or services furnished by the corporation, shall be sufficient at all times (1) to pay all operating and maintenance expenses necessary or desirable for the prudent conduct of its business, and the principal of and interest on the obligations issued or assumed by the corporation in the performance of the purpose for which it was organized, and (2) for the creation of reserves.