What the 15 percent standard requires
The REST did not jump straight to 15 percent. It set a schedule that climbed a little each year, starting low in the late 2000s and reaching the full 15 percent of retail sales in 2025. Renewable sources that count include solar, wind, some biomass and geothermal, and certain hydropower, with solar doing most of the work in a state that gets sun the way few others do.
Inside that target sits a smaller requirement people often miss. A portion of the standard, roughly 30 percent of the annual renewable amount under what the rule calls a distributed generation carve-out, has to come from small systems sited at homes and businesses rather than large plants out in the desert. Rooftop solar in neighborhoods from Ahwatukee to north Scottsdale counts toward this piece, and the surcharge on your bill is part of how the utilities have funded programs that support it.
Which utilities it binds, and which it does not
Arizona Public Service, the largest utility in the state and the one serving much of Phoenix proper, is regulated by the Commission and bound by the REST. So is Tucson Electric Power to the south. For customers of either, the 15 percent standard is a legal obligation the utility has to report against, not a voluntary goal.
Salt River Project is the exception that catches people out. SRP is a public power entity run by its own elected board, which places it outside the Commission's jurisdiction, so the REST does not bind it. Large parts of the metro, including much of Tempe, Mesa, and the east valley, are SRP territory, which means a lot of people who assume the state standard covers them are actually served by a utility that sets its own renewable targets instead. Check the name at the top of your bill before you assume.
How to read a compliance filing
Each regulated utility files paperwork with the Commission showing how it is meeting the REST, and those documents are public. The place to find them is the ACC eDocket (the Commission's online docket system, searchable at the agency's website), where you can look up a utility by name or by docket number and pull its annual REST implementation plan and compliance report.
When you open one, look for a few things. The headline is the percentage of retail sales served by renewables for the reported year, which you can set against the schedule. Then look at how much of that came from utility-owned or contracted generation versus renewable energy credits (tradable certificates that represent the clean attributes of a unit of power, bought and retired to show compliance). One honest caveat: these filings report on a year already finished, so the most recent one you find will usually lag the calendar by a year or more.
Worth watching this month
1. APS and Tucson Electric Power file their annual REST compliance reports with the Commission, so watch the ACC eDocket for the current filing, which typically appears in the first part of the year and covers the year before.
2. The Commission posts open meeting agendas on its website, and renewable or resource-planning items show up there from time to time; most are routine procedural steps, a few are not.
3. Salt River Project, which the REST does not bind, publishes its own sustainability targets, so SRP customers should watch srpnet.com rather than the state docket for commitments that affect them.
4. Integrated resource plans, the long-range supply plans utilities file, are where any direction for the years after 2025 tends to surface, so watch the ACC docket for the next round.