How the schedule reads
That schedule lives in APS's Integrated Resource Plan, the long-range filing (a utility's multi-year forecast of what it will build, buy, and close) submitted to the Arizona Corporation Commission. In it, APS lays out when each coal unit stops and what comes next. Cholla, near Holbrook and Joseph City, has stopped burning coal. APS's share of Four Corners, the plant across the line near Farmington, New Mexico, which APS operates and co-owns with other utilities, is set to wind down around the end of this decade, roughly 2031 at last public report.
The Coronado Generating Station at St. Johns belongs to Salt River Project, not APS, and SRP has said it plans to stop burning coal there by roughly the early 2030s. Group these together and the state's remaining coal capacity is on a path toward near zero within about ten years. Dates like these slip. A unit can get a short extension if a reliability risk shows up, so read any single year as a plan, not a promise.
The honest math on backfill
Replacing a coal plant is not a one-for-one swap. A coal unit runs on demand, day or night; solar runs when the sun is up, which in Arizona is a lot but not at 8 p.m. in July when demand is still high. That is why APS's purchases pair large solar fields with battery storage (banks that charge midday and discharge into the evening peak). The utility has been signing contracts for several hundred megawatts of solar and storage at a time, hedged here as "roughly" because final capacity shifts as projects clear permitting.
Whether the math closes depends on timing more than totals. If a coal unit retires in a given year and the solar-plus-storage meant to replace it is delayed in interconnection (the study-and-build process to plug a project into the grid), there is a gap, and the gap gets filled by natural gas or market purchases. So the honest answer to whether solar is replacing coal is this: yes in energy, mostly, and in capacity it depends on whether the batteries arrive on schedule.
Who owns what, and who decides
APS is the investor-owned utility, and its plans need Arizona Corporation Commission review, where five elected commissioners approve or push back on the Integrated Resource Plan. SRP is a public power provider with its own elected board, which is why Coronado's timeline is set in a different room than Four Corners'. The Navajo Nation and the Hopi Tribe were central to the Navajo Generating Station near Page and the mines that fed it, and tribal land and water underpin much of this fleet's history.
For replacement solar, the cast widens to private developers building on desert acreage and, increasingly, on tribal land leased for utility-scale projects. Watch who signs the power purchase agreements, because that tells you who carries the risk if a project runs late. The Commission's dockets are where these deals surface first, usually before any press release.
Worth watching this month
1. APS's current Integrated Resource Plan docket at the Arizona Corporation Commission, where any change to a coal retirement date would show up first, and this one actually matters.
2. SRP board materials on the Coronado Generating Station, which should confirm or adjust its coal-exit timeline, more routine than urgent.
3. EIA's generator data updates, which record when a unit's status flips to retired and make a good fact-check on any utility claim.
4. Interconnection queue updates for large Arizona solar-plus-storage projects, where delays would hint at a backfill gap before it reaches your bill.
5. Any Commission vote approving new APS solar or storage procurements, the clearest public sign the replacement plan is moving.