FlexGen to Integrate 380-MWh Hybrid Storage at MN8's Mammoth Solar

• FlexGen will integrate the storage at MN8 Energy's 86-MW Mammoth Solar project in West Virginia and supply its HybridOS energy management software.
• The software will run 70 MW / 280 MWh of lithium-ion and 10 MW / 100 MWh of Eos zinc batteries as one dispatchable resource.
• Google will buy the output; MN8 expects solar online in 2028 and the two storage blocks in 2029 and 2030.

FlexGen Power Systems will integrate the battery storage at MN8 Energy's Mammoth Solar project in West Virginia, where 70 MW / 280 MWh of lithium-ion batteries and 10 MW / 100 MWh of Eos zinc batteries are to operate as one dispatchable resource. The company announced the role in a statement on Nov. 11.

FlexGen will supply its HybridOS energy management software for the site, which also carries 86 MW of utility-scale solar. Before hardware ships, FlexGen plans to test the main system integrations at its North Carolina lab. Its remote operations center will keep commissioning going overnight. The statement did not name the lithium-ion battery supplier or the value of the contract.

MN8, Google and Eos Energy Enterprises unveiled the project on Sept. 2. Google will buy its energy, capacity and clean energy attributes for the PJM grid that serves its data centers in the region, including a planned facility in West Virginia, MN8 said. The solar plant is being built on a reclaimed coal mine in Kanawha County.

The project in numbers

• 86 MW of utility-scale solar, with commercial operation expected in 2028.
• 4 hours of storage from the 70 MW / 280 MWh lithium-ion block (list.solar calculation).
• 10 MW / 100 MWh of Eos Z3 zinc-based storage, designed for 10 hours.
• 380 MWh of storage in total, or about 4.4 MWh per MW of solar (list.solar calculation).
• 26% of that storage energy sits in the zinc batteries (list.solar calculation).
• Up to $350 million in capital investment and about 200 construction jobs, according to MN8 estimates.

FlexGen called Mammoth the first utility-scale zinc-based long-duration storage deployment in West Virginia. The company says it serves more than 25 GWh and over 200 storage systems, and its HybridOS codebase has logged over 13 million hours of runtime. Eos, which builds the Z3 systems in Pittsburgh, reported a 171% jump in third-quarter revenue on Nov. 5.

"Our roots in microgrids and our utility-scale experience give us the expertise to make diverse energy technologies operate as one coordinated power resource," Kelcy Pegler, FlexGen's chief executive, said.

MN8 expects the lithium-ion storage to follow the solar plant into commercial operation in 2029, with the zinc system in 2030.