As part of a one-and-a-half-year development project, VoltStorage has succeeded in developing a high-precision method for measuring the state of charge (SoC) of Redox Flow batteries. VoltStorage is setting new standards in Redox Flow research, as an accurate and serial producible SoC measurement has been one of the main challenges so far.
Challenge: Cost-effective Redox-Flow SoC measurement
Since the development of Redox Flow battery technology in the 1970s, this technology was mainly used in industrial storage systems. “For the operation of large storage systems, the development of cost-effective measuring methods was not necessary. The share of costs of existing measurement methods compared to the total costs of significantly higher priced large storage systems is quite low for large systems. However, the situation is different for home storage systems with significantly lower production and end customer costs. If we were using these existing cost-intensive measurement methods, we would not be competitive due to the high proportion of costs”, explains VoltStorage CTO Michael Peither, who heads the R&D department.
So far, no suitable standard components have been available on the market for our measuring needs. For this reason, VoltStorage relied on a method based on the so-called coulomb counting – a method commonly used in science to measure the state of charge. However, an inherent disadvantage of this method is its range of fluctuation, which can lead to inaccurate data in certain SoC areas.
Over 1.5 years development time for new state of charge measurement
With the aim of setting new standards in the field of Redox Flow technology, the VoltStorage R&D team has suceeded in developing a highly accurate and cost-effective state of charge measurement. With over one and a half years, five members of the VoltStorage R&D team evaluated a wide range of methods. “The vast majority of all measurement methods described in academic papers are simply not practical for implementation in mass produced energy storage systems,” explains Product Development Engineer Dr. Sean Ashton, who is responsible for the development of the new SoC measurement at VoltStorage.
The main reason is that, next to the targeted measurement accuracy, other aspects are also included in the evaluation of the method practicability. “In addition to the costs for the required measuring components, the serial producibility as well as the ease of integration into the battery system play a decisive role,” explains VoltStorage CTO Michael Peither. From the vast number of measurement methods described in the scientific literature, more than 30 methods were subjected to closer examination. Only three methods have finally made it into prototype development to provide more detailed assessments based on experimental tests.
New measuring method revolutionizes Redox-Flow state of charge measurement
The prototype tests in a laboratory environment have shown that one of the three tested measurement methods is particularly suitable for serial application in Redox Flow systems. “For competitive reasons, we cannot reveal the detailed method. But it is a measurement approach that enables a highly accurate state of charge measurement regardless of the Redox Flow cell chemistry,” explains project leader Dr. Sean Ashton. In addition, the measurement method enables a component design that can be easily and cost-effectively integrated into the battery system. VoltStorage’s internal electronics development department has developed a special “measurement board” for evaluating measurement data and calculating the SoC level.
Connected to the central control unit, this measurement board allows to use the SoC values for other operating system functions. For example, for the integrated rebalancing system, which is automatically activated when there is a charge imbalance between the negative and positive electrolyte tank. “The new high-precision measurement method has also positive effects on system functions that ensure the cycle stability of the entire system,” explains Dr. Sean Ashton.
Next steps: prototype use in series systems
Following the prototype development, selected series systems will now be equipped with the necessary measuring components. “After our successful laboratory tests, it is crucial that we now gain deeper insights into the new measurement method in a real-life environment – also in interaction with other system functions that rely on the SoC measurement,” explains VoltStorage CTO Michael Peither. If the further tests are as successful as before, the additional “measurement board” required for processing the measurement data will be integrated into the existing control unit of the energy storage system. “It is our goal to make the new measurement method available for all series systems in the future,” says Michael Peither.
In addition to the achievements in Redox Flow materials research, VoltStorage underlines its commitment to leadership in the Redox Flow field with the development of the state of charge measurement. “We are very glad that our investments in research and development are paying off so well. We have started with the objective of not only acting as a system integrator, but also to make a decisive contribution to the further development of Redox Flow technology. This is what significantly differs us from other competitors,” says VoltStorage CEO and Co-founder Jakob Bitner, explaining the strategic direction of VoltStorage’s R&D activities.
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