The actual output power of a 350 megawatt-hour (MWh) battery energy storage system in Europe is much lower than expected due to inconsistent batteries. Due to the failure of the battery management system to detect the fault in time, the tradable power is overvalued for a long time, and the balance cost risk is even as high as 110000 euros (about 127700 US dollars) per week.

This real failure case will be analyzed at the Battery Business and Development Forum to be held on April 1. The 350 megawatt-hour storage facility, located somewhere in Europe, also failed to meet revenue targets. Subsequent analysis showed that the situation could have been more severe.

This is similar to photovoltaic modules connected in series. The overall performance of the battery energy storage system ultimately depends on the weakest link. Lutz Morawietz, head of Volytica algorithm development, said: "Battery analysis data show that in this system, the cells with the highest state of charge have reached 100 percent, while the lowest is only 75 percent."

In the series structure, once the cell with the highest state of charge reaches the upper limit, other cells that have not yet been fully charged cannot continue to be charged. The discharge phase is also constrained by this: the cell with the lowest state of charge will be the first to be exhausted, forcing the battery management system to terminate the discharge process-resulting in the energy in the remaining cells not being used.

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