In 2010, a novel all vanadium redox flow battery system was developed at the US Department of Energy’s (DOE) Pacific Northwest National Laboratory (PNNL), with the support of the US DOE Office of Electricity Delivery and Energy Reliability’s Grid Storage Program. This new system uses vanadium electrolyte with chloride-containing supporting solution, in which a stable complex between Cl^- and V⁵⁺ forms. This new system was proved to have a much improved stability over the traditional sulfate based chemistry in small scales.

In the past three years, this advanced chloride-containin all vanadium redox flow battery system was extensively evaluated at UniEnergy Technologies, LLC (UET). The stability and cell performance of electrolyte solutions with different impurities were tested over a broad temperature window;  the performance of kW-scale and large-scale stacks was tested for thousands of cycles under various operation conditions; different testing and prototype systems, from 1 kW, 30 kW, to 100 kW, were developed and thoroughly tested for different applications; etc.

In 2014, the first commercial product of UET, Uni.System™, which delivers 600kW power and 2.2MWh energy in a compact footprint of only five 20’ containers, was successfully developed. This system integrates the abuse tolerant mixed acid vanadium electrolyte; a state-of-the-art containerized design derived from multiple decades of design experience among the UET team; optimized power electronics and controls at each system level (from cell to site); and mature large-scale stacks with more than 7 years of field deployment and over a dozen systems in the field.  In early 2015, a 1 MW-4 MWhr system, which consists of two Uni.System^TM, was deployed in Pullman, WA by a utility company, Avista.

In this presentation, we will discuss what we’ve learned in the past three years about this advanced chloride-containing all vanadium redox flow battery system, especially the unique advantages of this system over the traditional sulfate system, and our understanding on the potential of this novel technology for various energy storage market applications.