ESS: redox flow battery breakthrough?

ESS was established in 2011, incorporated in Oregon, and has c150 employees. The company went public in October-2021, via SPAC, raising $500M in new funds, valued at $1.1bn, and listing on NYSE.

It aims to be the leader in medium-duration energy storage (4-12 hours), with an iron flow battery costing 2-5c/kWh (assuming >daily cycling) and practically unlimited cycle life without degrading (>20,000 cycles). The first units have shipped and the company is now in the scale-up phase.

This is one of the highest-quality patent libraries that has crossed our screens, with excellent, specific and clear details; which have clearly locked up ESS’s implementation of an iron-based redox flow battery.

Five key challenges are identified in the file, along with helpful technical details of ESS’s innovations, all gleaned from reviewing its patents. In our view, the main bottleneck is round-trip efficiency, which may be dented by the electro-chemistry ESS uses to avoid side-reactions.

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