Tech giant supports a new way of storing energy. Grid stability is at stake.

One of the first commercial energy storage facilities in the United States based on compressed carbon dioxide technology will be built in Arizona. The project is being developed by Italian company Energy Dome in partnership with U.S. utility Salt River Project (SRP). The investment is expected to mark an important step in the advancement of long-duration energy storage while demonstrating how existing conventional power plant infrastructure can be repurposed for the energy transition.

New Project at a Former Coal Power Plant

The planned energy storage facility will have a power capacity of 19 MW and will be capable of delivering electricity for up to 10 hours. The installation will be located at the Coronado Generating Station in St. Johns, Arizona, and is expected to enter operation in 2029.

The project is financially supported by Google, which has entered into a cost-sharing agreement with the partners. The collaboration aims to accelerate the commercialization of energy storage technologies beyond the currently dominant lithium-ion battery systems.

Under a 20-year agreement, Energy Dome will own and operate the facility, while SRP will purchase and utilize the stored energy.

Giving Existing Energy Infrastructure a Second Life

A particularly notable aspect of the project is its location. The Coronado power plant, which historically operated on coal, is currently undergoing a transition that includes partial conversion to natural gas.

Locating the energy storage system on an existing energy site allows developers to leverage existing transmission infrastructure and grid interconnection rights. This approach can significantly reduce project development timelines by avoiding lengthy grid connection queues, which have become one of the major barriers to the expansion of renewable energy and energy storage projects.

Industry experts increasingly point to former coal plant sites as ideal locations for modern energy infrastructure, including battery storage systems, solar farms, and new power generation assets.

How Does the CO₂ Battery Work?

Energy Dome’s technology uses a closed-loop carbon dioxide cycle to store electrical energy.

During periods of excess electricity generation—such as from solar or wind farms—electricity is used to compress CO₂ and store it in liquid form. When energy demand rises, the carbon dioxide is reheated and expanded, driving a turbine that generates electricity.

According to the company, the system can provide energy for periods ranging from 8 to 24 hours while achieving a round-trip efficiency of approximately 70%. This means a significant share of the energy used to charge the system can be recovered and delivered back to the grid.

The technology is considered particularly attractive for applications requiring multi-hour energy storage, where conventional lithium-ion batteries become less cost-competitive.

Google Invests in the Future of Energy Storage

The Arizona project is one of the first outcomes of the strategic partnership between Google and Energy Dome. In 2025, the U.S. technology giant announced an equity investment in the company and launched a collaboration aimed at deploying CO₂-based energy storage systems near data centers worldwide.

Growing electricity demand driven by artificial intelligence and cloud computing services is pushing data center operators to seek solutions capable of ensuring reliable renewable energy supply around the clock.

Long-duration energy storage systems are increasingly viewed as a key enabler of these objectives.

Growing Interest in CO₂ Storage Technology

Energy Dome is expanding its technology beyond its partnership with Google. The company has operated a demonstration facility in Sardinia since 2022, where it has been supporting the Italian electricity grid.

In the United States, another project with a capacity of 20 MW and 200 MWh has recently been approved for Alliant Energy in Wisconsin. At the same time, the company has signed an agreement to deploy its technology at a planned 1 GW data center campus in Odessa, Texas.

The growing number of contracts suggests that CO₂-based energy storage could emerge as one of the most promising alternatives to lithium-ion batteries in the long-duration storage segment. For electricity systems with increasing shares of renewable energy, such solutions may play a crucial role in maintaining grid reliability and accelerating the energy transition.