GridStor Secures $220 Million for White Tank Battery Storage Project in Arizona

GridStor closed $220 million in debt financing for its White Tank battery storage project in Maricopa County, Arizona, on September 21, 2026, according to mgrid.org and Mercom Capital Group. The 100 MW/400 MWh GridStor White Tank battery storage project is backed by a 20-year tolling agreement with Arizona Public Service (APS), the utility that serves roughly 1.4 million homes and businesses in the state, and is expected to enter service in the first half of 2027.

ING Capital, KeyBank and Zions Capital Markets provided the financing package, structured as a combination of tax equity bridge, construction debt and term debt, mgrid.org reported. ING director Filipe Barreto said “the rapid growth of renewable generation is driving increasing demand for energy storage solutions, making BESS assets an integral part of energy infrastructure.”

Why the 20-year APS tolling deal made White Tank bankable

Under the tolling structure, APS pays for the right to charge and dispatch the battery, retaining the arbitrage upside and price risk itself, while GridStor receives contracted payments regardless of market power-price swings, according to mgrid.org’s analysis of the deal. That structure, rather than a merchant revenue model exposed to volatile wholesale prices, is what allowed lenders to finance the project on a non-recourse basis. mgrid.org’s reporting on the transaction noted the deal follows record peak electricity demand on the APS system, though it did not cite a specific figure for that peak.

The deal adds to a year of rapid battery deployment in the United States: US energy storage installations reached a record 20.2 GWh in the second quarter of 2026, and grid operators nationally are pairing new storage with rising demand from data centers, as seen in Eolian’s groundbreaking on Ohio’s largest battery storage project for an AI data center hub. For readers new to the technology, Winss Solutions’ explainer on grid-scale battery storage covers how duration and chemistry choices shape projects like White Tank.

Background: GridStor and Arizona’s storage build-out

GridStor is a battery storage developer backed by Goldman Sachs Asset Management, with more than 3 gigawatts of storage in development or construction across the western and central United States, according to mgrid.org. The White Tank close is GridStor’s fourth project financing in twelve months, following a $120 million financing for a Texas project in March 2026 and the acquisition of a 199 MW/796 MWh project in Colorado in May 2026. The White Tank project ties GridStor’s growth directly to Arizona’s largest utility, APS, whose 20-year tolling commitment gives the developer a contracted revenue stream through the mid-2040s as the state’s electricity demand continues to climb.

Sources: Mercom Capital Group; mgrid.org; SolarQuarter

Featured image: photo by Deane Bayas on Pexels (free Pexels license).

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Figen Sekin

I specialize in sustainability education, curriculum co-creation, and early-stage project strategy. At WINSS, I craft articles on sustainability, transformative AI, and related topics. When I’m not writing, you’ll find me chasing the perfect sushi roll, exploring cities around the globe, or unwinding with my dog Puffy — the world’s most loyal sidekick.