EnerVault

The company's core business was designing and manufacturing long-duration, megawatt-hour scale energy storage systems. Its primary technology was an iron-chromium redox flow battery, a concept originally pioneered by NASA. This technology stores energy in liquid electrolytes held in external tanks, allowing for the independent scaling of power (the size of the cell stack) and energy capacity (the volume of the electrolyte). This modularity offered a cost-effective solution for long-duration storage, as increasing capacity simply required more electrolyte, making it a viable alternative to gas-fired peaker plants. EnerVault's patented "Engineered Cascade™" architecture was developed to enhance the stability and reliability of the conventional iron-chromium flow battery design.

EnerVault targeted utility operators, renewable energy producers, and large industrial clients, offering solutions for time-shifting energy, providing grid stability services, and ensuring power reliability. The company successfully deployed a utility-scale demonstration project in Turlock, California, featuring a 250 kW, 1 MWh system co-located with a solar array and irrigation pumps. This project, supported by grants from the U.S. Department of Energy and the California Energy Commission, proved the technology's viability in a real-world setting. Despite raising over $24 million from investors like Mitsui, Total Energy Ventures, and 3M, EnerVault failed to secure subsequent funding to advance to full commercialization. In 2015, the company announced it was seeking new owners and subsequently underwent an assignment for the benefit of creditors, effectively ceasing operations.