Tuesday's decision follows tense hearings this summer in Boise where utilities, developers and environmental groups tussled. Boise-based Exergy Development Group suspended hundreds of millions in Idaho wind and biogas projects, blaming uncertainty over what the rules would eventually look like for scaring off its financiers.
Exergy officials didn't immediately respond to requests for comment Tuesday.
In a key ruling, commissioners decided PURPA-eligible projects are entitled to ownership of their renewable energy credits, or "RECs," that can be sold for millions of dollars to utilities in states with renewable portfolio standards. For renewable projects that don't qualify under PURPA, utilities and developers will share RECs equally.
"Revenues from the sale of RECs continue to provide a revenue stream to ... developers to encourage the development of renewable generation," the PUC concluded.
Rocky Mountain Power, a utility serving southeastern Idaho, was among those arguing that RECs should belong to the utilities.
Rocky Mountain spokesman Jeff Hymas in Salt Lake City said his company was reviewing the decision.
"We will implement the policy set by the commission and will continue to provide high-level customer service to independent power producers," he said.
For existing wind farms, Tuesday's ruling didn't contain just gloomy news.
It rejected Idaho Power's demands for more freedom to halt contractually required electricity purchases during periods of light load, such as at night when the wind is blowing but few people are using power.
"Idaho Power did not provide sufficient evidence to support its proposal," the commission wrote. "If the company believes that over-supply ... presents operational problems during light-load periods then it should this address issue when it negotiates new power purchase agreements."
This follows a separate, federal decision earlier this year that also blocked the utility's curtailment demands.