Copper Valley Project

Executive Overview

The Copper Valley Project is a 500 MW / 4,000 MWh advanced compressed air energy storage (A-CAES) facility in early development by Hydrostor, Inc. (doing business as Copper Valley Energy Storage LLC) in the City of Buckeye, Maricopa County, Arizona. The project filed a ten-year transmission plan and ninety-day generation plan with the Arizona Corporation Commission in early 2026, representing the project's first major regulatory step in the state. The facility would connect to the grid via a new approximately four-mile 500 kV transmission line linking to the Jojoba 500 kV substation, jointly owned by Arizona Public Service and Salt River Project. Hydrostor submitted a generator interconnection application to SRP's Generator Interconnection Process in February 2026, with impact studies to follow. Commercial operation is targeted for September 30, 2032. No offtake agreements or project financing have been publicly disclosed at this stage.

How It Works & Differentiation

The facility uses Hydrostor's proprietary A-CAES technology: surplus grid electricity drives compressor trains that pressurize ambient air into purpose-built underground hard-rock caverns located approximately 2,000 to 2,600 feet below surface, organized into four 125 MW trains each comprising compressors, heat exchangers, and turbines/expanders. Heat generated during compression is captured and stored in thermal storage tanks rather than vented — and returned to the expanding air during discharge — eliminating the fossil fuel combustion that characterizes conventional CAES designs. A water column maintains constant air pressure as caverns fill and empty, improving round-trip efficiency. The system provides eight hours of continuous discharge at full 500 MW output, with a 100–150 acre surface footprint. Like all Hydrostor projects, Copper Valley is designed for a 50-year operational life, provides synchronous inertia and black start capability, and produces zero greenhouse gas emissions during operation.

Commercialization & Traction

The ACC filing is the project's first public disclosure and represents early-stage regulatory engagement rather than a final investment decision. Hydrostor's project pipeline identifies Arizona/Maricopa County as one of several active U.S. development markets, alongside California (Willow Rock), New York, and Nevada — all 500 MW projects at varying stages. Willow Rock received final permitting approval from the California Energy Commission in December 2025 and represents Hydrostor's most advanced U.S. project. The company's global pipeline exceeds 7 GW across North America, Australia, and the UK, and it is backed by Goldman Sachs Alternatives, CPP Investments, and Canada Growth Fund. No utility offtake, state procurement process, or project-level financing has been identified for Copper Valley at this time.

Scalability & Strategic Context

Arizona faces rapidly growing electricity demand driven by data centre development, semiconductor manufacturing, and population growth across the Phoenix metro — structural conditions that create durable demand for dispatchable long-duration storage. The Jojoba 500 kV interconnection point sits within the high-growth West Valley transmission zone, and the project's 8-hour duration is suited to address the multi-hour peak demand events that characterise Arizona's extreme summer afternoons. Copper Valley is part of Hydrostor's deliberate strategy to advance projects across multiple markets before long-duration storage procurements mature — positioning the company to compete once state policy frameworks and utility integrated resource plans create clear procurement pathways, as has occurred in California with Willow Rock's offtake agreements.