The deployment of renewable energy technologies such as photovoltaic solar panels and wind turbines partly relies on large energy storage options because the intermittent energy production is not synchronized with consumer demands. A flow battery, an electrochemical energy conversion device which shares features with both batteries (recharge needed) and fuel cells (reactants circulate), has a high energy efficiency and a more easily scalable power (cell stack size) and capacity (reactant tank size) than batteries. However, the flow battery cost is still too high to support commercialization efforts. The Hawaii Natural Energy Institute is investigating the tradeoff between salt purity and cost, and energy efficiency for the all vanadium flow battery, the most developed system, to reduce battery cost.

Vanadium oxide sulfate (VOSO4) salts of different purities ranging from 97 % to 99.99 % were first acquired. Subsequently, the activity and reversibility of the vanadium reactions in a solution containing the dissolved salt (4+ oxidation state) was determined by an electrochemical analysis method (cyclic voltammetry). Chemical analysis methods (inductively coupled plasma – mass spectrometry, total organic carbon) will be used to identify impurities and their concentration in solutions that will enable a correlation with the activity and reversibility of vanadium reactions and the identification of the elements causing the observed loss in efficiency. Vanadium oxide sulfate solutions will be spiked with the identified harmful species to confirm assessments. Analyses and tests will be conducted for all other 3 vanadium oxidation states (5+, 3+, 2+), which will require sequential charging and discharging steps of the vanadium oxide sulfate solutions. All solutions will be analyzed by titration to confirm the concentration of vanadium species and ensure results comparability. The experimental database will be used to gauge vanadium salt purity options.

Point Person: Jean St-Pierre


Flow Battery







Gills Onions Flow Battery Systems

Flow Battery. Electrolyte is stored in tanks and pumped through the core to generate electricity; charging is the process in reverse. The volume of electrolyte governs battery capacity. Courtesy: Battery University   One of the world’s largest vanadium flow battery energy storage systems began operation earlier this year at Gills Onions, an Oxnard, Calif., fresh-cut onions processing plant. The tennis court–sized system consists of cell stack modules that are connected in parallel configurations. It stores electricity during lower-cost nighttime hours and allows the Gills facility to rely on the flow battery to generate 600 kW for as long as six hours during higher-cost peak hours. Courtesy: Gills Onions