Cal. Public Utilities Code § 371

(a) Except as provided in Sections 372 and 374, the uneconomic costs provided in Sections 367, 368, 375, and 376 shall be applied to each customer based on the amount of electricity purchased by the customer from an electrical corporation or alternate supplier of electricity, subject to changes in usage occurring in the normal course of business. (b) Changes in usage occurring in the normal course of business are those resulting from changes in business cycles, termination of operations, departure from the utility service territory, weather, reduced production, modifications to production equipment or operations, changes in production or manufacturing processes, fuel switching, including installation of fuel cells pending a contrary determination by the Energy Commission, enhancement or increased efficiency of equipment or performance of existing self-cogeneration equipment, replacement of existing cogeneration equipment with new power generation equipment of similar size as described in paragraph (1) of subdivision (a) of Section 372, installation of demand-side management equipment or facilities, energy conservation efforts, or other similar factors. (c) This section does not exempt or alter the obligation of a customer to comply with Chapter 5 (commencing with Section 119075) of Part 15 of Division 104 of the Health and Safety Code. This section does not limit the ability of residential customers to alter their pattern of electricity purchases by activities on the customer side of the meter. (d) Enhancement or increased efficiency of equipment, as described in subdivision (b), shall include industrial process heat recovery technology that meets the requirements of Section 451.7.