GridStor Closes $220 Million Financing for a 400 MWh Arizona Battery

Goldman Sachs-backed GridStor has closed $220 million of financing for its 100 MW / 400 MWh White Tank battery in Maricopa County, Arizona, under a 20-year tolling agreement with the utility Arizona Public Service.

The financing

ESS News reported on 22 September that the package combines a tax equity bridge, construction and term debt, provided by ING Capital, KeyBank and Zions Capital Markets. It is described as GridStor's fourth financing in the past 12 months. The company says it is building or acquiring more than 3 GW of batteries. White Tank is expected to start operating in the first half of 2027.

What a tolling agreement means

Under a tolling agreement, the utility pays the battery owner a fixed fee for the right to charge and discharge the battery as it sees fit. The owner does not take the risk of price swings in the wholesale market, which is why lenders like it. Arizona Public Service serves about 1.4 million customers, per Enerdata's summary of the company's release.

Why Arizona wants storage

Both reports link the project to rising demand. APS set a peak demand record on 2 August 2026, 5 per cent above its 2025 record. ESS News attributes the growth to population, manufacturing, particularly chip fabs, and data centres. A battery can charge when solar is plentiful at midday and discharge during the evening peak, when air conditioning demand remains high but solar output has faded.

Context for home battery buyers

Utility-scale deals like this one are growing fast in the United States, as our report on record quarterly storage additions shows, while the home segment is under different pressures. Our United States guide covers what that means for households. The two kinds of battery do similar work on the grid but serve different buyers: a tolled project is paid by a utility, a home battery by the household that owns it.

ESS News's article contains two small inconsistencies, a stray reference to a different company name and two versions of the lender's name, so we have used the names that appear in both sources.

Sources

• ESS News: GridStor wins financing for 400 MWh BESS in Arizona, tolling secured with state utility
• Enerdata: GridStor secures USD220m for a 100 MW/400 MWh BESS project in Arizona

Related guides

Keep reading, or check your own numbers:

• US adds a record 20.2 GWh of storage in Q2
• Home batteries in the United States
• Home batteries and the grid: problem or solution?