Hi André, Thank you for your kind response. I work for a PV company here in Mexico, and I'm actually running this simulation because a client wanted a proof that the systems he purchased (and designed) will not work correctly. I've accepted to run the simulation and thought it would be very obvious that the results will be much more favorable for a system with 72 cell system working alongside a 24V battery bank, however for my surprise, I got the exact opposite results. Just to give some background, on real life operation, the systems stopped working after about a year because dead batteries. This is consistent with the info of the manufacturer of the battery, stating about 340 cycles @ 0% DOD. The system has a 100 W charge running all night, and at the end the system was only capable of turning the load for 3 hours, so I think the real energy flowing to the batteries is about 25% of the design energy. When running the same model in PVsyst, but changing modules, I get 1,039 kWh/yr for 2S2P 125 Wp modules and 1,166 kWh/yr for 1S2P 250 Wp modules. Just for reference, I have 2S2P 115 Ah @ 12V batteries on both models. As you can see I'm getting 11% higher production on 60 cell system. Should I introduce another parameter to get more accurate results? Is there a not so obvious reason for the model to output higher energy yields on 60 cell model? Good day!