Validated Analytical Model to Project and Price New Flow Batteries for the Grid

Abstract

A more renewable electrical grid is demanded by exacerbating fossil fuel depletion and environmental repercussions. Among renewables, wind and solar photovoltaics are expected to see the fastest growth1,2, notwithstanding their inherently variable supply. To sustain the pace of renewable development, then, calls for electrical energy storage (EES) technologies, which would ease integration and allow higher capacity. However, given the anticipation that electricity costs remain below 14 cents per kilowatt-hour for decades to come2, EES devices must above all be cost-effective. Redox flow batteries (RFBs) are a standout EES candidate3. Unlike in a traditional solid-state battery, in an RFB, electrolytes are stored external to the electrode; as such, RFBs enjoy good efficiency, durability, and safety. More notably, RFBs see independently designable power and energy capacity. Further flexibility is possible in both redox chemistries and cell/stack design. At the same time, the breadth of possible innovations for RFBs tends to confound the question of cost-effectiveness. Indeed, to evaluate a new RFB for the grid requires either risky scale-up ventures (for experimental studies) or a comprehensive, generalizable model (for theoretical studies). We present the latter, with characterization of: activation overpotential in reaction networks, ohmic overpotential in concentrated electrolytes, concentration overpotential in different membrane-electrode configurations; as well as stack losses. Requisite characteristic parameters can be validated by independent experimental measurements. We also validate our overall model for a range of chemistries, layouts, and scales (Figure 1). In doing so, we demonstrate nearly instantaneous screening of new designs, an indispensable approach to both inform and direct future RFB development.