Several parties appeal from the district courts judgment affirming a final order of the Public Utility Commission ("the Commission") setting cost-of-service rates for the transmission and distribution utility ("TDU") of Reliant Energy, Inc. ("Reliant"). After a contested case proceeding, the Commission entered an order setting rates below the level Reliant sought for its TDU. Reliant and several parties who intervened at the agency level sought review by the district court. The district court concluded that one of the Commissions findings of fact was a prohibited advisory opinion, but otherwise affirmed the Commissions order. Reliant, Gulf Coast Coalition of Cities ("Gulf Coast"), Office of Public Utility Counsel ("OPC"), and Consumer Owned Power Systems ("COPS") all challenge the district courts affirmance of the Commissions order. We will reverse the portion of the district courts judgment affirming the Commissions inclusion of $107.3 million for the interconnection of Merchant Plant 4. We affirm the district courts judgment in all other respects. We remand the case to the Commission for further proceedings.