California ISO settles ‘tagging’ issue with Mesquite Solar 1 project

The California ISO on Sept. 30 filed with the Federal Energy Regulatory Commission an executed Large Generator Interconnection Agreement (LGIA), to be made effective on Jan. 1, 2014, between the ISO, San Diego Gas & Electric (SDG&E) and Mesquite Solar 1 LLC.

The Mesquite Solar LGIA is a non-conforming LGIA, which provides for the interconnection of the 165 MW solar photovoltaic facility located near Arlington, Ariz. The Mesquite Solar LGIA includes certain provisions to reflect the ISO’s discussions with the Salt River Project, the operator of a balancing authority area (BAA) adjacent to the ISO. These discussions and the associated provisions of the Mesquite Solar LGIA account for the unique nature of the generating facility’s interconnection, CAISO noted.

CAISO also offered to FERC notice of termination of a Pilot Pseudo-Tie Participating Generator Agreement between the ISO and Mesquite Solar, effective February 2012. This agreement was replaced by a pro forma Pseudo-Tie Participating Generator Agreement, ISO Service Agreement No. 2905, on that date.

Mesquite Solar submitted an interconnection request in July 2010 for this generation project, identified as Queue Position #643T in CAISO’s interconnection queue. Mesquite Solar subsequently submitted a request to downsize the net output of the facility to 165 MW in accordance with the ISO Tariff Appendix GG. This request was accepted pursuant to the Generator Downsizing Study Report: Area Report in the San Diego Gas & Electric’s System, issued on July 8, 2013.

Mesquite Solar has an existing interconnection comprised of two 500 kV generation tie lines between the Hassayampa Switchyard and the Mesquite 230/500 kV Switchyard. Together, the Hassayampa Switchyard, Palo Verde Switchyard, and three bus ties between the two switchyards form the Common Bus at Palo Verde. Two 500 kV transmission lines under CAISO operational control are connected to the Common Bus: the Hassayampa-Hoodoo Wash line and the Palo Verde-Devers line.

The Mesquite Solar generating facility is currently participating in the ISO markets as a “pseudo-tie resource.” As a pseudo-tie resource and because the Hassayampa Switchyard is under SRP’s control, CAISO requires the generation schedules to be tagged with SRP as the native balancing authority area. This arrangement prevents the capacity from being considered as deliverable for purposes of counting for resource adequacy purposes in the same manner as resources located within the CAISO balancing authority area.

Concurrent with the ISO interconnection process, Mesquite Solar engaged in discussions with representatives of the CAISO and SRP to find a solution that would allow the generating facility to obtain full capacity deliverability status utilizing the facility’s existing connection to the Hassayampa Switchyard. As a result, Mesquite Solar, SRP, and the ISO considered several options that could be pursued to achieve the Mesquite Solar’s deliverability objective. These discussions led ultimately to the awareness that the Common Bus Arrangement could facilitate a solution without the need to construct additional interconnection facilities. CAISO and SRP have concluded that the existing Common Bus Arrangement permits CAISO to receive the power output of Mesquite Solar or other similarly situated generating facilities without requiring tagging.

Sempra U.S. Gas & Power and Consolidated Edison Development recently became equal partners in two of Sempra U.S. Gas & Power’s solar facilities; the 150-MW Copper Mountain Solar 2 near Las Vegas and Mesquite Solar 1. Under the terms of the joint-venture agreements, which were announced in May, each company will own a 50% interest in each of the solar facilities. The terms of the transaction were not disclosed.

“Copper Mountain Solar 2 and Mesquite Solar 1 are among the largest photovoltaic solar plants in the U.S., and we are pleased to partner with ConEdison Development in the ownership of both these plants,” said Kevin Sagara, vice president of renewables for Sempra U.S. Gas & Power, in a Sept. 23 statement. “This transaction enables us to improve our financial returns, deconsolidate debt and reinvest the proceeds to more rapidly grow our business.”

Mesquite Solar 1, the first phase of Sempra U.S. Gas & Power’s Mesquite Solar complex located in Arlington, Ariz., was completed in late 2012. Power from the facility has been fully sold to Pacific Gas & Electric under a 20-year contract.

About Barry Cassell 20414 Articles
Barry Cassell is Chief Analyst for GenerationHub covering coal and emission controls issues, projects and policy. He has covered the coal and power generation industry for more than 24 years, beginning in November 2011 at GenerationHub and prior to that as editor of SNL Energy’s Coal Report. He was formerly with Coal Outlook for 15 years as the publication’s editor and contributing writer, and prior to that he was editor of Coal & Synfuels Technology and associate editor of The Energy Report. He has a bachelor’s degree from Central Michigan University.