What is the Problem?
Large-scale batteries generate heat during charging and discharging events. So, we are interested to know the impact of charge/discharge regime on the generated heat. Also, it is quite important to quantify the impact of excessive heat in terms of battery degradation.
Why is it Interesting?
Since batteries in large-scale application sit in an enclosed container, the generated heat should be removed as fast as possible. This will improve battery operation in terms of available capacity, available charge, and round-trip efficiency. To do so, active and passive cooling mechanisms are employed in such applications. However, excessive heat leads to over-consumption of the active cooling system. This will, in turn, reduce the overall efficiency of the plant.
What is the Approach?
In this study, we utilised operational data of a 600kW/760kWh battery within a 3.2MWp PV plant at the University of Queensland campus in Gatton, QLD, Australia. Through the data analyses, we show that both charging and discharging events increase battery temperature substantially. We also found a strong linear relationship between current and temperature of the battery during discharge events. Such as strong correlation has not been identified during charging incidents. We also found out that the extra battery degradation caused by the excessive heat is substantial.
What is New?
This is the first study of its kind to show such impact for large-scale battery systems using real-world operational data. The linear relation between the temperature and current during discharging events is a remark with huge consequences which is made in this paper. The difference identified between charging and discharging regimes on battery temperature is yet another significant insight presented in this study.
How was it Tested?
First, we selected charge and discharge events where the ambient temperature had nothing to do with the temperature rise. Then, we developed several measures (such as Temperature Rising Slope, Peak Temperature, Absolute Temperature Change, Peak Current, Total Charge, and Temperature Rising Delay) to conduct analyses. After that, we tried to find a linear or piecewise linear relationship between the measures and battery temperature during the event. Finally, we used Zhurkov model quantify the extra degradation occurred due to excessive temperature.