Flow batteries allow energy and power components of electrical storage systems to be independently configured. The energy capacity (kWh) of a flow battery is easily increased by storing additional electrolyte within the system of fixed power (kW), thereby increasing duration of energy delivery. The rated power of flow batteries may be raised by increasing membrane surface which increases the area of electroactivity for a higher power output.
Flow battery technologies are mainly distinguished by electrolyte composition such as the single electroactive-element vanadium redox battery or dual electroactive-element designs such as the Fe – Cr and Zn – Br batteries.
Vanadium redox flow batteries are considered a leading light of the push towards technologies that can meet the need for long-duration energy storage - Andy Colthorpe (Energy Storage News)
The vanadium redox flow battery (VRFB also VRB) employs vanadium ions in different oxidation states to store chemical potential energy in an electrolyte solution. VRFB exploits the novel ability of vanadium to exist as four stable oxidation states V2+, V3+, V4+ and V5+ in acidic aqueous solutions. This property allows a flow battery design with a single electroactive element instead of two.
Vanadium batteries offer excellent characteristics compared to alternatives: extended service life, no discernible degradation of electrodes or electrolytes after thousands of rapid charge-discharge cycles, superior safety due to lack of combustibles and good operability across a wide range of ambient temperatures. Vanadium-based electrolyte is classified as a non-toxic fluid per UN regulations so no onerous permitting, is completely reusable and recyclable and has a low incremental cost for increased duration of energy output.
VRFB generally has higher energy capacity compared to competing batteries so it is well-suited for long-duration storage in static applications. These include off-grid applications with PV or wind, load shifting and load levelling within national grids, as well as smoothing of intermittent supplementary generation from renewables feeding into national, regional or local grids. Lithium batteries, on the other hand, typically are of higher power density and short-duration storage capacity so these batteries are best suited for applications where rated power is more important than duration such as EV and other mobile storage requirements.
The VRFB is a compelling alternative to lead acid or lithium battery technologies promising significant TCO savings in long-duration storage applications. It is widely recognised as a potential driver for sustained growth in vanadium demand over the medium and longer term.
Vanadium occurs naturally in about 65 minerals and is recovered from vanadium-bearing titaniferous ores, steel-making slags and a range of secondary resources such as spent petrochemical catalysts, combustion residues of fly ash, petcoke cinder and stone coal.
Primary vanadium producers only account for about a fifth of vanadium output globally. Secondary resources contribute around 10% with the balance of output (70%) produced as a by-product in the steel industry. Currently there are only three primary producers worldwide: Bushveld, Largo and Glencore. Largo currently leads with the highest annual output but Bushveld has the largest installed capacity globally so they are favourably positioned to overtake Largo’s Maracas operation. Both Largo and Bushveld already are strongly focused on VRFB with dedicated energy subsidiaries spun out in a vertically integrated business model.
X GROUP has developed a viable ion exchange (IX) flowsheet for producing VRB electrolyte directly from calcine seepage and vanadium process effluents as well as various secondary resources. Ongoing efforts to further improve the world’s lowest cost VRB electrolyte are focussed on minor adjustments to the acidic matrix, V3+ V4+ ratio and chemical stability.
An important differentiator of the X GROUP process is the capability to produce high-purity vanadyl sulphate solution at the required 1.8M concentration in a liquid-only flowsheet without any precipitation of solids required.
Watch this space!
Flow Battery Energy Storage Technology