A joint agency is hereby authorized to fix, charge and collect rents, rates, fees and charges for electric power and energy and other services, facilities and commodities sold, furnished or supplied through the facilities of its projects. For so long as any bonds of a joint agency are outstanding and unpaid, the rents, rates, fees and charges shall be so fixed as to provide revenues sufficient to pay all costs of and charges and expenses in connection with the proper operation and maintenance of its projects, and all necessary repairs, replacements or renewals thereof, to pay when due the principal of, premium, if any, and interest on all bonds and other evidences of indebtedness payable from said revenues, to create and maintain reserves as may be required by any resolution authorizing and securing bonds, and to pay any and all amounts which the joint agency may be obligated to pay from said revenues by law or contract.