The grid frequency is identical throughout the entire continental European interconnected grid (ENTSO-E) and serves as an important parameter for the current status and stability of the electricity grid. The target frequency in continental Europe is set at 50Hz. As it is not possible to store electricity directly in the grid, supply and demand in the grid must be balanced. If the frequency falls, this means that the demand for electricity is greater than the power currently being fed into the grid. If the frequency rises, there is too much electrical power in the grid. Smaller frequency fluctuations around 50Hz are balanced out by control reserve products such as frequency containment reserve. Larger frequency fluctuations are compensated for by other control products such as automatic frequency restauration reserve. The graph shows the measured grid frequency over the last 30 minutes. Stronger frequency deviations can be observed around full hours in particular. If you are further interested in the topic of grid frequency and the European electricity grid, a detailed analysis of the grid frequency is available here:  10.1016/j.egyr.2024.12.057 

An EPR of at least 0.81h is required for the frequency containment reserve (FCR) in Germany. The graph shows the energy throughput for pure FCR operation from 2018 to 2024. With an EPR of 1h, this results in approx. 300 EFC per year with a slight variation depending on the year in focus. With a different storage design, the EFC changes accordingly. Consequently, higher EPR designs result in lower cyclization of the batteries.

Note: this graph does not take into account the necessary recharging management.

The cumulative amount of energy for the respective service provided is shown here on a daily and monthly basis. A distinction is made between charging and discharging. Since battery energy storage systems also incur losses (transformers, converters/inverters, and battery packs), the amount of energy charged is always greater than the amount of energy discharged. The following services are shown:

• frequency containment reserve (FCR)
• automatic frequency restauration reserve (aFRR)
• Redispatch
• Wholesale

The services shown can be superimposed during operation so that the sums of the energy quantities shown for each service/product do not correspond to the physical energy throughput of the battery storage system at the grid connection point.

The Battery efficiency describes how much of the energy stored in a battery can be used again when it is discharged. At the battery pack level, not only the cell efficiency is considered, but also the losses that occur in the connecting cables, the battery management system (BMS), the balancing and the cooling systems. For M5BAT, the cooling system is not part of the efficiency determination.

The graph can be used to estimate the efficiency at battery pack level. The energy throughput per battery unit per month is considered here. An error can be entered in the value due to a difference in the state of charge at the beginning and end of the month. This becomes smaller as the energy throughput increases. Efficiency values in the range of 90 to 95% are shown for all lithium-based battery units.

For batteries, the number of cycles completed is an important parameter for assessing service life and performance. Each battery can only run through a limited number of cycles until the end of its service life. Capacity and performance decrease continuously. Depending on the cell chemistry, the batteries have different cycle resistance and age at different rates depending on the cycle depth, temperature and current load. The graph shows the daily equivalent full cycles (EFC) of the M5BAT battery storage system. It can be seen here that the LTO battery unit cycles more, as this is a more cycle-stable technology. Depending on the operating mode and load, there are different equivalent full cycles per day.