No ordinance granting a franchise or granting a renewal or extension thereof shall be valid unless it shall expressly provide therein that the price to be paid by the City for the property that may be acquired by it from such utility by purchase, condemnation or otherwise, shall exclude all value of such grant, extension or renewal, and unless it shall expressly provide therein that the rental price to be paid by the City shall exclude all value of such grant, renewal or extension.