The SunZia transmission project includes the development of a 550-mile-long transmission line by Pattern Energy. Credit: Pattern Energy.
The ground-breaking ceremony for the SunZia transmission project was held in September 2023. Credit: Pattern Energy.
SunZia transmission will be developed consequently with the SunZia wind project. Credit: Mrs_ya via Shutterstock.

SunZia transmission project, also known as the SunZia Southwest transmission project, is a 550-mile long high-voltage direct current (HVDC) transmission line being developed in New Mexico, US.

Pattern Energy, a renewable energy developer owned by the Canada Pension Plan Investment Board (CPPIB) is developing the project.

The SunZia transmission project broke ground in September 2023 and is expected to start commercial operation in 2025.

The HVDC link will provide the Southwest with 3GW of clean, renewable power. It will be the largest voltage source converter (VSC) installation in the US and one of the largest worldwide.

The transmission line is being developed concurrently with the 3.5GW SunZia wind project.

The two projects will make up the largest renewable energy infrastructure project in the US and generate more than 2,000 job opportunities.


The SunZia transmission line is being developed between Corona, New Mexico, and Pinal County, Arizona.

Development background

The SouthWestern Power Group, a private construction services firm and a subsidiary of the MMR Group, acquired the development rights for the SunZia transmission project from Energy Capital Partners and its four partners, Salt River Project, Tucson Electric Power, and Shell Wind Energy, in 2008.

The transmission project received an approved rating of 3GW (east-to-west) in January 2015, for two single-circuit 500kV AC transmission lines running from central New Mexico to south-central Arizona.

Pattern Energy acquired the SunZia transmission project from the SouthWestern Power Group in July 2022, which included the rights to develop two transmission lines, each extending 550 miles.

A notice for the revised Preliminary Operating Scheme plan of service was submitted to the members of the Western Electricity Coordinating Council in July 2022.

The plan included the development of a transmission line as an HVDC bipole transmission project utilising a voltage source converter, along with a revised comprehensive progress report for review.

The Arizona Corporation Commission approved the Certificate of Environmental Compatibility application for the SunZia transmission line in November 2022.

In May 2023, the Bureau of Land Management announced the record of the decision for the transmission project, marking the completion of the National Environmental Policy Act process.

SunZia transmission project details

The SunZia transmission project includes the development and construction of a bipole (2 x 1.5GW) ±525kV HVDC transmission line extending 550 miles (885.14km).

Two HVDC converter stations named SunZia East DC in New Mexico and SunZia West in Arizona will be developed as part of the project.

The converter stations will feature HVDC Light® technology and the MACH digital control platform from Hitachi Energy.

The converter station in New Mexico will convert the power from AC to DC for transport in the overhead lines while the converter station in Arizona will convert the power back to AC for integration into the receiving grid.

In addition, two 0.75mi 500kVac tie lines will be developed from the SunZia West converter station to integrate into the Pinal Central substation

The power infrastructure will include a 345kVac switching station, known as the Pete Heinrich 345kV switching station, and two AC choppers (dynamic braking resistors).

SunZia transmission line route

The transmission line will start at the new substation in Torrance County, New Mexico, and end at the existing Pinal Central 500kV substation in central Arizona.

It is planned to pass over Lincoln, Socorro, Sierra, Luna, Grant, Hidalgo, Valencia, and Torrance counties in New Mexico and Graham, Greenlee, Cochise, Pinal, and Pima counties in Arizona.

The transmission line will follow the same corridor as the Western Spirit transmission line developed by Pattern Energy as part of the Western Spirit Wind Project.

Technology details

The transmission line’s converter stations will feature the HVDC Light technology, a VSC technology that enables power to be transmitted over long distances.

The technology enables compact converter stations and offers benefits such as neutral electromagnetic fields, and oil-free cables, resulting in minimal losses and maximum power quality. and

The line will also feature the MACH digital control platform, which enables advanced fault registration and remote control options. It enables the transmission line to be controlled and operated reliably.

Project financing

Pattern Energy announced the completion of an $11bn non-recourse financing in December 2023.

This comprehensive package encompasses an integrated construction loan and letter of credit facility, two distinct term facilities, an operating phase letter of credit facility, an innovative tax equity term loan facility, and a holding company loan facility.

For the approximately $8.8bn allocated to construction and term facilities, a consortium of banks and financial institutions including BNP Paribas, Crédit Agricole Corporate and Investment Bank, CoBank, ACB; Desjardins Group, Export Development Canada, ING Capital, Intesa Sanpaolo’s New York Branch, KFW IPEX-Bank, MUFG Bank, National Bank of Canada, Natixis Corporate & Investment Banking, Societe Generale, Sumitomo Mitsui Banking Corporation, and Wells Fargo Securities.

The $2.25bn tax equity term loan facility was facilitated by Banco Santander’s New York Branch and Santander Bank, acting as Joint Coordinating Lead Arrangers. Bank of America, GE Vernova’s Financial Services business, Natixis Corporate & Investment Banking, and the Royal Bank of Canada.

Nomura Securities International, and CPPIB Credit Investments III, a subsidiary of the CPPIB, contributed to the final segment of the financing arrangement.

Contractors involved

Hitachi Energy, a sustainable technological solution provider, was awarded a contract to provide HVDC and other advanced technologies for the SunZia transmission project in May 2023.

Hitachi Energy in collaboration with Quanta Services, an infrastructure solution provider, will provide solutions such as managing the construction, building, and installation of HVDC at the project site.

Quanta Services was also contracted to deliver a turnkey solution for the SunZia transmission project in May 2023.