October 17, 2025: Iron flow BESS developer ESS Tech has announced the closing of a $40 million financing deal.

The BESS manufacturer said on October 14 the financing with YA II PN, an investment fund managed by Yorkville Advisors Global, provides $30 million of immediate capital.

An additional $10 million will be available on execution of an at-the-market sales agreement with Yorkville Securities, an affiliate of Yorkville, subject to customary conditions.

ESS said the capital strengthens its cash position and signals significant momentum following its announcement on October 5 of plans to connect a pilot 5MW/50MWh iron flow BESS to the grid in Arizona for the Salt River Project (SRP), a not-for-profit public power utility.

The pilot will be installed at SRP’s Copper Crossing Energy and Research Center and sell capacity to SRP under a 10-year energy storage agreement.

ESS said the move will help SRP evaluate emerging, non-lithium ion long-duration energy storage (LDES) technologies and support SRP’s reliability and sustainability goals.

The system, using ESS’ Energy Base technology, will store enough energy to power 1,125 average-size homes for 10 hours, ESS said.

Last year, ESS said its Energy Warehouse BESS had been granted seismic design certification from the Institute of Electrical and Electronics Engineers.

The system received the highest level of IEEE 693, which ESS said made it the first non-lithium, LDES provider to receive the certification.