Google Backs West Virginia Solar Project With 380 MWh of Short- and Long-Duration Storage

Google, MN8 Energy and Eos Energy Enterprises announced September 2 that the Google Mammoth Solar storage project in Kanawha County, West Virginia, will combine 86 MW of solar generation with 380 MWh of two different battery technologies, creating a dispatchable resource for the PJM grid serving Google’s regional data centers. The project matters because it pairs conventional lithium-ion storage with a 10-hour zinc battery system rather than relying on one storage technology to shift solar generation across different time periods.

MN8 will own and operate the project, which includes 70 MW/280 MWh of lithium-ion storage and 10 MW/100 MWh of Eos Energy Enterprises’ Z3 long-duration storage system. According to the September 2 joint project announcement, Google will purchase the project’s energy, capacity and clean-energy attributes under a long-term agreement as it adds new electricity resources to grids serving its data centers.

Mammoth Solar combines three complementary resources

The project is designed around three technologies rather than a conventional solar-plus-battery configuration.

Its 86 MW photovoltaic array provides generation. A 70 MW/280 MWh lithium-ion battery provides four hours of nominal storage at full rated output. A separate 10 MW/100 MWh Eos Z3 system is designed for 10 hours of discharge.

MN8 says combining the two storage technologies allows the project to turn intermittent solar generation into a more dispatchable resource whose output can extend across more hours of the day.

That distinction is important. Lithium-ion storage can shift substantial amounts of solar generation across several hours, while longer-duration storage can address periods that exceed the economical or practical duration of many conventional battery installations.

Microgrid Media previously examined the same underlying challenge through Google’s planned use of 100-hour iron-air storage for a Minnesota data center, illustrating how hyperscalers are increasingly testing multiple long-duration technologies rather than relying exclusively on lithium-ion batteries.

The Eos system will provide 10 hours of storage

Eos will supply 10 MW/100 MWh of its Z3 zinc-based battery technology.

The system is designed to discharge for 10 hours, extending energy availability beyond the shorter-duration lithium-ion portion of the project. Eos says Mammoth Solar will be Google’s first project using its Z3 technology and the first deployment under a previously announced master supply agreement between Eos and MN8.

The company describes its aqueous zinc chemistry as a non-lithium storage technology designed for applications requiring approximately four to 16 or more hours of duration.

Independent September 3 reporting from ESS News confirms that the project combines 100 MWh of zinc storage with 280 MWh of lithium-ion capacity and that the storage was added as the Mammoth Solar development progressed through West Virginia’s regulatory process.

The project is designed around data center load growth

Although Mammoth Solar will connect to the PJM grid rather than operate as a dedicated behind-the-meter data center plant, its commercial purpose is closely tied to Google’s electricity demand.

The companies say the integrated portfolio will add dispatchable capacity to the grid serving Google’s regional data centers, including a planned West Virginia facility.

Google will purchase the energy, capacity and clean-energy attributes from Mammoth Solar. That structure means the project adds a new grid-connected resource rather than physically wiring the solar and batteries exclusively to one computing campus.

The distinction matters as data center developers experiment with several different power models, from grid-connected renewable procurement to large behind-the-meter data center microgrids combining onsite generation and battery storage.

The project will be commissioned in stages

Mammoth Solar will not enter service as one completed portfolio.

MN8 expects the solar portion to reach commercial operation in 2028. The lithium-ion battery system is scheduled to follow in 2029, with the Eos long-duration storage planned for 2030.

Those dates remain development targets rather than completed milestones and are subject to construction, financing, procurement, interconnection and regulatory risks.

The project is being developed on a reclaimed coal mine in Kanawha County. MN8 estimates total capital investment of as much as $350 million and approximately 200 construction jobs.

West Virginia gets its first commercial-scale long-duration storage project

MN8 and Eos describe Mammoth Solar as West Virginia’s first commercial-scale long-duration energy storage deployment.

The project also links a state with a long history of coal production to an emerging battery-manufacturing supply chain. Eos maintains manufacturing operations in Pennsylvania, and the company emphasizes domestic production of its zinc-based systems.

Long-duration storage is increasingly being evaluated as grids add variable renewable generation and large new electricity loads. The technology does not replace lithium-ion batteries in every application; Mammoth Solar instead demonstrates how developers can use both technologies within one portfolio.

That multi-duration architecture may be particularly useful when a project needs both relatively high-power short-duration response and lower-power energy delivery extending further into the evening or other periods without solar generation.

The project is significant but not yet operational

The Google Mammoth Solar storage project remains a development-stage asset.

Its significance therefore lies in the commercial structure and technology selection rather than current electricity production.

The first major milestone will be completion of the 86 MW solar project in 2028. Lithium-ion storage would then add four-hour shifting capability in 2029, followed by the 10-hour Eos system in 2030.

If those stages proceed as planned, Mammoth Solar will provide a real-world test of whether combining short- and long-duration battery technologies can create a more dependable solar resource for a regional grid facing rapidly increasing data center demand.