Tenn. Code § 67-6-346
There shall be a credit of one hundred percent (100%) of the sales and use tax paid with respect to any system, method, improvement, structure, device or appliance appurtenant thereto that is required and primarily used to bring the purchaser into compliance with pollution control laws or regulations, whether federal, state, or local, when such pollution is created in the course of the purchaser's regular business activities. The credit provided in this section shall not be available to persons primarily engaged in processing, treating, or controlling pollution created by others. Copies of certificates provided for in § 67-5-604 or other evidence that is satisfactory to the commissioner shall be furnished to the commissioner by the purchaser to establish entitlement to the credit. The credit provided in this section shall also apply to machinery and equipment used to produce or store electricity in a certified green energy production facility, as defined in § 67-4-2004. A copy of the facility certification issued by the department of environment and conservation shall be furnished to the commissioner by the taxpayer to establish entitlement to the credit. Instead of taking the credit available under this section or § 67-6-507(i) and (j), the purchaser may apply to the commissioner for a refund of the taxes paid or for authority to make purchases exempt from the tax.
T.C.A. § 67-6-346