BESS simulation result - Losses

[Ady]

Dear PVsyst Team,

We have a question regarding the battery losses displayed in the simulation output. The BESS loss parameters in PVsyst appear to reflect only certain categories of losses, and in our case, the "Battery Global Loss" is shown as approximately 1.9%.

However, since the round-trip efficiency (RTE) of the battery is around at 85%, we would expect the total battery-related loss to be closer to 15%. Could you please clarify why only 1.9% is reflected in the simulation report?

Is there a reason the full impact of the RTE is not shown under the battery loss section, or is it accounted for elsewhere in the system losses?

Appreciate your guidance on this matter.

[André Mermoud]

First of all: the value 1.9% is related to the total energy flux of the system. The real "round trip" efficiency of the battery pack should be related to the energy passing through the battery. This is mentioned as 5.3% here.

I don't know where your affirmation of 85% comes from. This is extremenly fluctuating according to sources. Some Li-Ion battery manufacturer mention 95% on their datasheets (which is probably not realistic), others 90%, rarely less.  

Due to the extreme complexity of the battery model, especially the SOC evolution according to the charging/discharging balance, the determination of the battery efficiency cannot be quite reliable in the PVsyst simulation.  This issue is fully explained in the help https://www.pvsyst.com/help/physical-models-used/batteries/battery-model/battery-efficiency.html?h=battery+efficiency