All Liquid RFB ( Development Timeline ):
Redox flow batteries, which have been developed during the last 40 to 50 years, are used to store energy on the medium to large scale, particularly in applications such as load leveling, power quality control and facilitating renewable energy deployment. Redox flow batteries offer an attractive solution to grid-scale storage due to independent scaling of power and energy, long service life, and simple manufacturing.
Early developments were carried out by NASA in the 1970s for bulk storage of electrical energy, load leveling, and to facilitate the use of intermittent energy sources such as photovoltaic cells and wind turbines. NASA studied a variety of redox couples, but their early focus was on the iron-chromium RFB. Between 1973 to 1982 iron-chromium RFB system with power / capacity of up to 1 kW/13 kWh were designed, fabricated and tested. Since 1981, NASA redirected the emphasis on fundamental studies of RFBs and stopped the system level effort. The Moonlight Project in Japan was designed to further develop RFB, and manufactured and tested 10 kW/60 kWh system prototypes from 1984 to 1989. Zinc RFBs development was in parallel with the iron-chromium RFB. The first 10 kW and 100 kW zinc-chlorine RFBs were tested then a 2 MW/6 MWh unit was designed for electric utility demonstration. Japan installed a 1 MW/4 MWh zinc-bromine RFB system in 1990. At present, the zinc bromine RFB is being developed by RedFlow Ltd in Australia. Since 2009 ViZn Energy has been developing the Zn-Iron RFB from 50 kW to 1.4 MW.
The limited abundance and cost of the raw materials, particularly for RFB’s using redox-active metals and precious-metal electro-catalysts is now the limiting factor of wide-scale utilization of flow batteries. Recently, lower cost actives species such as metal-free redox couples and hybrid RFB have been center of attention.
Hybrid RFB ( Development Timeline ):
Redox flow batteries also might be classified into groups according to the phases of the electroactive species presented in the system. In the classical RFB. No phase change occurs on the electrodes; all electroactive species remain soluble, e.g., the all-vanadium RFB. However in Hybrid RFB:
Type I: at least one of the electrode reactions involves a phase change, such that some of the electroactive species are in the solid or gaseous phase. If electrodeposition takes place at an electrode, then the volume of the half-cells limits the storage capacity. Although their feasibility has been well demonstrated by the commercial Zn-Br RFB, these systems can be prone to blocked manifolds due to detached solids/dendrites, edge effects at electrodes and flow inlet/exit effects. In hybrid systems involving metal deposition, e.g., Zn-Ce and Zn-Br, slow self-discharge can take place by deposit corrosion. It is also difficult to achieve thick deposits during mixed or mass transport-controlled conditions.
Type II: Phase change at both electrodes in the cell. Both half-cell reactions involve phase changes at the electrode surfaces during charge and discharge, as in the soluble lead RFB, where lead ions in an acidic solution are reversibly converted to PbO2 on charge at the positive electrode and metallic lead at the negative one. The energy is stored as deposits in the two electrodes, and the inter-electrode volume limits its capacity.
World Energy Outlook expects total renewable used in the electric power sector to increase. The rapid growth in variable renewable energy, namely solar PV and wind, is catalyzing efforts to modernize the electricity system. Energy storage investment has continued to increase as more renewable energy is integrated into energy mix, as a measure to mitigate climate change. This ensures that system stability is maintained by matching supply and demand of electricity. Large / medium battery storage is one of the options for enhancing system flexibility in these circumstances by managing electricity supply fluctuations. Current global market size of vanadium electrolyte is ~ 400 MWh of annual electrolyte production capacity. However, less than 1% of the world vanadium consumption can be attributed to battery use. Lack of domestic supply of vanadium electrolyte, keep the local price high. The overall market is set to expand dramatically in the coming decade.