Sonoran Substation to Wilmot Energy Center 138 Kilovolt Transmission Line

Tucson Electric Power (TEP) is planning to build a new 138-kilovolt (kV) substation, transmission lines and a switchyard south of Tucson to strengthen electric reliability for customers, meet future energy needs in the area and support what will become TEP’s largest local community-scale solar array and battery storage system.

The planned 100-megawatt (MW) solar array and accompanying 30 MW energy storage system located at the Wilmot Energy Center (WEC) will be owned and operated by an affiliate of NextEra Energy Resources. The systems are expected to be in service by the end of 2020 and will provide enough renewable power to serve up to 21,000 homes annually.

In spring 2018, TEP transmission planners reduced the scale of the project because transmission studies indicated that existing and planned infrastructure would support the new facilities and that new connections to TEP’s South Loop Substation in Sahuarita were unnecessary. The project name was updated as the “Sonoran Substation to Wilmot Energy Center” transmission line project, which includes three major components.

  • The Sonoran Substation will connect TEP’s existing 138 kV transmission system to the WEC. It also will house transformers and other equipment to reduce voltage from TEP’s 138 kV transmission voltage to lower voltages for delivery to customers. The additional capacity will help improve reliability by reducing the stress placed on existing circuits, and support customer growth in the area. TEP plans to build the Sonoran Substation on about 40 acres at a site located southeast of East Old Vail Connection and South Swan roads.
  • The Cisne Switchyard, which will be located within the WEC, will interconnect the new solar and battery storage systems to TEP’s electrical system through the proposed 138 kV facilities.
  • A 138 kV transmission line will extend more than a mile to connect the Cisne Switchyard to the new Sonoran Substation. Additionally, new 138 kV transmission lines will connect TEP’s existing 138 kV transmission system along East Old Vail Connection Road to the Sonoran Substation. The lines will cross private land in Tucson and unincorporated Pima County.

The Arizona Power Plant and Transmission Line Siting Committee, a committee established by the ACC, reviewed TEP's application during a public hearing held in September 2018 and recommended approval of a Certificate of Environmental Compatibility (CEC) for the transmission lines and switchyard.

The City of Tucson also approved a Special Exception Land Use Permit in December 2018 that allows for construction of the substation after TEP filed an application and hosted a public meeting for neighbors in 2018.

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