Tenn. Code Ann. § 67-6-307

There is excluded from the sales and use tax base that portion of the consideration, received from the sale of steam produced by an energy or resource recovery facility owned or operated by a municipality, that is used to satisfy an indebtedness to the state incurred pursuant to title 68, chapter 211, part 4 [repealed]. This exclusion shall only apply if the facility has no more than one (1) customer, and the portion of the consideration subject to the exclusion is separately stated on each billing. In the event ownership of the facility is transferred to the facility's sole customer, that portion of the consideration previously excluded from taxation shall be taxable to the customer.