New SunZia transmission line is a plus for reliability and affordability
In 2023, when the California Independent System Operator (CAISO) sought approval of its new Subscriber Participating Transmission Owner (SPTO) initiative from the Federal Energy Regulatory Commission (FERC), Pattern Energy’s SunZia Transmission project became one of the first lines to apply for that status.
Approved by FERC in 2024, the subscriber model allows transmission developers outside the CAISO’s balancing authority footprint to finance transmission infrastructure, join the CAISO balancing area and transfer operational control to the CAISO when the transmission line is energized. This is done using a cost-recovery mechanism different than the CAISO’s traditional transmission access charge which is paid for by load within and exports from the CAISO balancing authority footprint. Under the SPTO model, the transmission developer enters into a subscriber agreement with the power generator who then uses power purchase agreements with end-use customers to recover construction and financing costs. This innovative structure supports important Western transmission development and enables consumers to obtain generation resources necessary to meet reliability and clean energy objectives.
“Working with CAISO under the SPTO model, we appreciated its transparency and collaboration,” said Deral Danis, Vice President of Transmission for Pattern. “It is great to work with an organization that starts with ‘yes’ and figures out how to make it happen.”
The 550-mile line has been designed to deliver up to 3,650 megawatts (MW) of New Mexico wind energy to Arizona and the CAISO grid, and the CAISO’s share of that power is 2,100 MW.
“SunZia is meeting surging energy demand with new interregional transmission infrastructure that can deliver reliable, affordable energy,” Pattern said in a June 18 news release announcing that the line was fully operational. “The project helps solve one of the central challenges facing the energy sector: not only building energy generation, but also the grid infrastructure needed to deliver that power.”
SunZia brings another operational benefit to the CAISO balancing authority footprint. Its New Mexico wind generation provides valuable diversity to California's renewable portfolio. While California’s prolific solar generation typically reaches its maximum output during the middle of the day before declining sharply in the late afternoon and evening, SunZia's wind production often strengthens during those same hours, with summer wind patterns frequently ramping through the late afternoon and into the evening as low-level, jet-stream conditions develop. This complementary production profile helps supply clean energy during the net load peak, when system needs are greatest and solar resources are declining.
Successfully integrating and forecasting a renewable resource of this scale also demonstrates the CAISO's growing capability to manage an increasingly diverse and interconnected clean energy fleet while enhancing reliability across the region. It’s the kind of transmission project that represents the long-term infrastructure investment needed to serve customers today and strengthen the grid for the future.
