Okla. Stat. tit. 68, § 2357.1

As used in this section and Section 2357.2 of this title, "solar energy system" means a system primarily designed to provide heating or cooling, electrical or mechanical power, or any combination thereof by means of collecting, transferring or storing solar generated energy for such purposes. Such term shall include passive structural and nonstructural features which are designed to provide a calculated net energy gain to a structure from renewable energy sources, commonly referred to as "passive solar energy systems", but shall not include those parts of a structural system which would be required regardless of the energy source being utilized. Solar energy may be derived from either direct processes or indirect processes using wind energy systems.