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Battery Management System for Vanadium Redox Flow Batteries
Vanadium is an element that can commonly exist in four different oxidation states, namely an ion with different charges, e.g. a vanadium ion that is missing three electrons would have a charge of V3+. Adding an electron converts it to a V2+ ion. This transfer of electrons back and forth is what makes Vanadium Redox Flow Batteries (VRFB) charge and discharge. A conventional VRFB consists of two tanks of vanadium-based electrolyte dissolved in water and separated by a proton exchange membrane.
At around 50°C, the ions present in a VRFB begins to crystalise and precipitate within the electrolyte solution. This hinders the redox reactions necessary to generate electricity. An existing solution is to empty the batteries during stand-by, however this inevitably causes a delay in the response time when electricity is required, as the cells need to be filled again. Furthermore, the emptying process can cause a depression within the cells, as this favors the entry of air, causing undesired reactions between atmospheric oxygen and the electrolytes. Alternatively, forced ventilation is used to avoid the precipitation of electrolytes but this has proven to be a complex, costly and energy consuming solution.
Based in Italy, the technology owner has developed a proprietary battery management system (BMS) designed to increase efficiency and longevity of VRFB. The BMS controls the temperature of the electrolytes in order to avoid the precipitation of vanadium salts in the solution, thus preventing the redox reaction from being halted, and avoiding battery damage. The BMS can also improve the battery’s response time, which is suitable when VRFBs are used for quick regulation of grid frequency.
The BMS has been tested on an industrial scale electrochemical energy storage set-up at a university in Italy. The system algorithm currently runs on LabVIEW platform and the software can easily be transferred to common industrial controllers such as programmable logic controller (PLC). The technology owner is seeking industry or research partners to license and adopt the technology.
Technology Features, Specifications and Advantages
- The BMS software is capable of interacting with the different hardware elements to which it is connected: signal conditioning system, power management system, hydraulic circuits, cell and stack voltage and current, open circuit voltage (OCV), input and output stack temperature, stack current, electrolyte flow rates, stack pressure drops, tank levels, pump power, etc.
- By acquiring a multitude of parameters, the BMS can control battery functions, in particular: (a) identify a period of inactivity of the battery, during which it does not either accumulate or supply power; (b) Activate an operational mode to maintain the accumulated charge during stand-by that:
- Interrupts the electrolyte flow from the stack to the battery or maintains a minimum flow necessary to guarantee adequate battery response time.
- Identifies the threshold condition at which salts can precipitate within the stack. Consequently, activates a washing cycle that pumps fresh electrolyte solution from the tanks. This action is particularly important because in controls the stack temperature and avoids overheating.
- Advantages include maintaining battery charge even during stand-by avoiding self-discharge; effectively avoid the precipitation of the electrolyte inside the cells during battery stand-by by identifying threshold conditions and operating effective correctional measures; and control the temperature of the electrolyte inside the cells.
- Energy storage systems within electrical grids (smart grids, micro-grids) for management, control and characterisation of redox flow batteries.
- Industrial redox flow battery installations including multiple stack installations.
- Test facilities for VRFBs.
- This technology looks to the electrochemical energy storage market, which is closely tied to the production of electricity from renewable resources. Electrochemical energy accumulators are frequently used in various stationary applications such as domestic end-user, microgrids and DSO/TSO distribution grids.
- In particular, 50% of the flow battery market uses Vanadium Redox Flow Batteries, which in 2020 was worth approximately $194 Million (USD) and is estimated to grow by a CAGR of 20.9% by 2027 (Global Industry Analysts, Vanadium Redox Battery – Global Market Trajectory & Analytics, (2021).