Section 39.453 - Customer Choice and Relevant Market and Related Matters(a) The commission may not authorize customer choice until the commission certifies the applicable power region as a qualifying power region under Section 39.152(a). Sections 39.152(b)-(d) also apply to the electric utility and commission in determining whether to certify the applicable power region.(b) The commission shall certify that the requirement of Section 39.152(a)(3) is met for an electric utility subject to this subchapter only if the commission finds that the total capacity owned and controlled by the electric utility and the utility's affiliates does not exceed 20 percent of the total installed generation capacity within the power region of that utility.Added by Acts 2005, 79th Leg., Ch. 1072 (H.B. 1567), Sec. 1, eff. June 18, 2005.