--- title: "Arizona's AI power boom now turns on a 63-year-old coal plant and a rate case" description: "Pinnacle West trades at a premium to Duke on the expectation that Arizona's data-center-driven load doubles and compounds into earnings. Whether it compounds, or lands on household bills, is now a decision for the state's utility commission, with a coal plant's life and a rate case in the balance." publisher: "The Inference" section: "Power" published: 2026-10-18T23:06:13.319Z modified: 2026-10-18T23:06:13.319Z canonical: https://theinference.org/article/arizona-s-ai-power-boom-now-turns-on-a-63-year-old-coal-plant-and-a-rate-case language: en keywords: "Data Centers, Utilities, Coal, Arizona, Regulation" --- # Arizona's AI power boom now turns on a 63-year-old coal plant and a rate case > Pinnacle West trades at a premium to Duke on the expectation that Arizona's data-center-driven load doubles and compounds into earnings. Whether it compounds, or lands on household bills, is now a decision for the state's utility commission, with a coal plant's life and a rate case in the balance. The AI build-out in Arizona has left the engineering stage and entered the accounting one. Arizona Public Service (APS), the state's largest electric utility, [told investors this month](https://www.industrialinfo.com/news/article/capex-plan-for-arizona-utility-shows-broadening-of-states-economy--363553) that it now expects electric sales to grow 5-7% a year through 2030, up from 4-6% [1]. Its 2025-2028 capital plan rises to about $10.8 billion [1]. The first physical consequence is a 63-year-old coal plant [1][2], and whether all that spending compounds into earnings now rests with the Arizona Corporation Commission, not with the data centers. ## The doubling is booked, not forecast Compute is the load. In Arizona the buyers are data centers and the chip fabs clustering around them, and sales to those extra-high-load-factor customers are up 13.6% so far this year [1]. APS put the scale in one line [on the Nameplate podcast](https://x.com/NatBullard/status/2110447074617745442): "It took us 140 years to get to nine gigawatts, and we're going to double that over the next 10 to 15 years" [3]. Behind the committed growth sits a queue APS has not signed but says it must be ready to serve: more new demand than the entire grid the utility spent a century building [1]. *Chart: **APS must be ready for uncommitted load more than twice the grid it runs today** Bar chart comparing APS peak demand in 2025 with committed demand growth and the uncommitted load queue, in gigawatts* *Nameplate figures in gigawatts from APS's October 2026 investor presentation, as reported by Industrial Info Resources. Committed growth is a lower bound and no year was given; the queue is load APS says is not yet committed. [1]* ## The first move is to keep coal running Generation comes before wiring. APS's current resource plan had it exiting the Four Corners plant, its last coal station, in 2031 [2]. [A confidential September agreement](https://www.kjzz.org/business/2026-10-05/aps-signs-agreement-that-could-extend-four-corners-coal-power-plant-use-until-2038) with Navajo Transitional Energy Company, whose mine supplies the plant's coal, could keep it running until 2038 [2]. APS says staying longer lowers customer costs [2]; the mine and plant also provide about 35% of the Navajo Nation's general fund [4]. The updated resource plan that settles the plant's future reaches the commission this month [2]. ![Four Corners Power Plant seen across its cooling pond in June 1972, smoke rising from several stacks](https://storage.googleapis.com/theinference-public/img/450ecb62d3e63507.jpg) *The plant and its cooling pond in June 1972, as APS prepared its expansion. The mine and the plant supply about 35% of the Navajo Nation's general fund, one reason its life is contested. (Lyntha Scott Eiler, U.S. National Archives and Records Administration)* ## Who pays for the growth is the contested layer Pricing sits on top of the plant. APS has proposed "[direct assignment of generation costs (to large loads)](https://theinference.org/article/amazon-google-meta-and-microsoft-sign-duke-energy-s-data-center-tariff-ratepayers-keep-the-exit-risk) to ensure growth pays for growth" [1]. That principle is disputed on the record: [a consumer advocate alleges households and small businesses paid $587 million toward data-center growth between 2023 and 2025](https://azcapitoltimes.com/news/2026/10/09/data-center-costs-divide-corporation-commission-candidates/), an analysis APS calls misleading, while in its open rate case APS is seeking a 45% increase on large-load customers [5]. Residential customers get a $14 credit on their November bills [6], and two commission seats are on the same month's ballot [5]. ## The premium waits on the commission [Pinnacle West](https://theinference.org/markets/companies/pinnacle-west-capital), APS's parent, [trades at 19.85 times earnings](https://www.ad-hoc-news.de/boerse/news/nebenwerte/pinnacle-west-stock-trades-at-19-85-times-earnings-versus-duke-s-18-24/70350161) against [Duke Energy](https://theinference.org/markets/companies/duke-energy)'s 18.24 [7]. That premium pays for the doubling before anyone has ruled on who funds it. The load is observable; the price is a projection until the commission decides the rate case and the resource plan. Growth paying for itself is the right design, and the fastest way to keep building. The dated markers are the plan this month and third-quarter results before the open on November 3 [7]. The doubling is booked. The invoice is still being negotiated. ## Takeaway APS guides to 5-7% annual sales growth through 2030 and a $10.8B capital plan, but a deal that could run the Four Corners coal plant to 2038 and a contested rate case leave the earnings verdict to Arizona regulators. ## Sources 1. [Industrial Info Resources (IIR News Intelligence), "Capex Plan for Arizona Utility Shows Broadening of State's Economy," 12 October 2026](https://www.industrialinfo.com/news/article/capex-plan-for-arizona-utility-shows-broadening-of-states-economy--363553) 2. [KJZZ (Greg Hahne), "APS signs agreement that could extend Four Corners coal power plant use until 2038," 5 October 2026](https://www.kjzz.org/business/2026-10-05/aps-signs-agreement-that-could-extend-four-corners-coal-power-plant-use-until-2038) 3. [Nat Bullard, post on X quoting APS on the Nameplate podcast, October 2026](https://x.com/NatBullard/status/2110447074617745442) 4. [PR Newswire via Morningstar, "APS Extends Four Corners Power Plant Operations Beyond 2031" (Navajo Transitional Energy Company), 1 October 2026](https://www.morningstar.com/news/pr-newswire/20261001dc62162/aps-extends-four-corners-power-plant-operations-beyond-2031) 5. [Arizona Capitol Times (Reagan Priest), "Data center costs divide Corporation Commission candidates," 9 October 2026](https://azcapitoltimes.com/news/2026/10/09/data-center-costs-divide-corporation-commission-candidates/) 6. [Arizona Public Service (@apsFYI), post on X, APS customers to receive November bill credit, October 2026](https://x.com/apsFYI/status/2110029299353108710) 7. [ad-hoc-news.de, "Pinnacle West stock trades at 19.85 times earnings versus Duke's 18.24," 18 October 2026](https://www.ad-hoc-news.de/boerse/news/nebenwerte/pinnacle-west-stock-trades-at-19-85-times-earnings-versus-duke-s-18-24/70350161) --- Arizona's AI power boom now turns on a 63-year-old coal plant and a rate case — The Inference. Canonical: https://theinference.org/article/arizona-s-ai-power-boom-now-turns-on-a-63-year-old-coal-plant-and-a-rate-case