The authority and any municipality or public or private entity operating an electric utility, or a municipality or private entity and another municipality or private entity, may enter into a contract providing for or relating to the sale of electric power by the authority to the municipality or entity, or by the municipality or entity to another municipality or entity. The contract may provide
(1) that the amounts payable under the contract are operating expenses of the utility and are valid and binding obligations of the municipality or other entity payable from the gross revenues of the utility;
(2) for one or more appropriations of the amounts payable under the contract;
(3) for the municipality or other entity to assume the obligations of another contracting party in the event of a default by that party;
(4) that after completion of a project the municipality or other entity is obligated to make payments notwithstanding a suspension or reduction in the amount of the power supplied by the project; or
(5) that payments under the contract are not subject to reduction by offset or otherwise.