Performance Testing of a Megawatt-Scale Battery Storage for Energy Trading

Large-scale battery energy storages (BESS) are being used more and more for various applications such as system services in the power grid. The importance of their use in short-term energy trading, such as day-ahead and intraday trading, has been growing steadily due to increasing and more dynamic energy prices. In current technical and economic simulations and trading models, batteries are often represented as energy reservoirs that can charge and discharge a constant power within a specified time frame, which can lead to significant discrepancies between planned and physical delivery. Since batteries and consequently BESS cannot deliver the same power over the whole state of charge (SOC) range, their real operating ranges and limits have to be investigated in order to successfully use BESS in energy trading. With an intraday performance test of the lithium-manganese-oxide (LMO) batteries of our hybrid BESS M5BAT, we show capabilities and limitations of the battery units. The results show that the LMO batteries meet the performance and requirements of the intraday market over a wide SOC range. However, especially in the upper and lower SOC ranges, the power available from the batteries is reduced. When parameterizing trading models for batteries, special attention has to be given to the efficiencies of the batteries, power electronic components and transformers under the respective load points so that the deviations between the trading plan and reality do not become too large. Based on our results for a relatively aggressive profile, we find that LMO batteries are well suited for short-term energy trading applications, adhering to safe temperature levels in the case of our system. Further, we find that with the appropriate knowledge of efficiencies, short-term BESS operations can be optimized with sufficient accuracy. Using the example of M5BAT, this work provides insights in performance characteristics of the operation of BESS.