I agree with you at a first glance but it is possible to match your value with the one obtained by PVsyst. In example, if you have a consumption of 10 thousand Ah per day, and it´s needed an autonomy of 2 days and on the other hand you need to incorporate in your design a DOD of 70% maximum. The calculation is as follows: Battery Capacity = (10000Ah/day X 2 days)/ (0,7) = 28571 Ah; Then, taking into account the self-discharge and efficiency of the battery, we have: 28571 Ah X 0,95 = 27142 Ah Comparing this value to the one obtained by PVsyst Simulation: Go to the main menu - Preferences - Hidden parameters - Category: Standalone System Presizing : change the value of "SOC minimum Threshold" to 30% (if you want to fix the maximum DOD at 70%) and also in the same Category change the value of "Battery Capacity: C100/C10 ratio" to 120%. With these values it is obtained a suggested value of 26510 Ah; we have only 2,38% oversized capacity comparing our calculation to the PVsyst simulation. Note: The lower value we have in C100/C10 ratio, the higher value we obtain in capacity , but the usually ratio is between 120 and 130%. We must to fix some values in the Hidden parameters menu if we want to obtain the expected values or at least similar. I hope this could help you. Kind regards
