Leaders of Washington’s energy permitting council advanced a plan on Wednesday that would cut by one third the size of the state’s largest proposed wind and solar energy plant.

The state’s Energy Facility Site Evaluation Council indicated it will require developers of the Horse Heaven wind project near Kennewick to incorporate extensive setbacks from historic bird nesting sites, marking a possible resolution to a yearslong debate over protections for the locally endangered ferruginous hawk.

The energy council, which can override local bans on wind and solar power, plays a key role in Washington’s green ambitions. But it has struggled to referee battles between renewable energy developers and a diverse coalition of power plant opponents, a Cascade PBS investigation found earlier this year.

Colorado-based developer Scout Clean Energy first pitched building more than 200 wind turbines, along with solar arrays and battery storage systems, on a prominent ridgeline near the Tri-Cities in 2021. Scout warned in a July letter that the new restrictions, combined with others already imposed by regulators, would cut the project’s generating capacity by 348 megawatts.

The Yakama Nation, Benton County and local homeowners have vigorously opposed the project and sued the state to stop its construction.

EFSEC approved the project last year, after then-Gov. Jay Inslee rejected an initial curtailment plan. But the agency punted final determinations over hawk nesting buffer zones to a technical advisory group.

That group examined 45 historic hawk nests and found just one of them occupied. Advisory group members agreed that 40 other nests were no longer viable habitats. But group members disagreed about the size of buffer zones around five nests found to be viable.

EFSEC staff sided with the most restrictive plan favored by some in the advisory group: a two-mile buffer zone around the five viable nests. Wind and solar equipment would also need to stay at least one kilometer away from the non-viable nests.

Scout argued that agriculture and urban development have already degraded the habitat in question, making it unlikely the birds will return. Ferruginous hawks spend little time in Washington anyway, the company added, and are not listed as endangered in any other states or federally. It called the decision to protect inactive nests “unprecedented.”

“With the exception of the single active nest in 2025,” project manager Dave Kobus wrote, “the 0.6 mile setbacks are intended to protect a resource that simply no longer exists in the Horse Heaven Hills.”

The Horse Heaven project represents a key piece of the state’s strategy to reduce carbon emissions amid a spike in electricity demand. Forecasts predict electric vehicles, heat pumps and data centers will require Washington to double its electricity output in the next 25 years.

Last month, Gov. Bob Ferguson rejected a 160-megawatt solar energy plant EFSEC had approved in Klickitat County. He told the Council to work more closely with the Yakama Nation to resolve tribal concerns about impacts to the landscape.

EFSEC may formally vote on the Horse Heaven restrictions in October.