I've been a PVsyst user for some time and am now trying to perform some simulations using SAM. As you know, the two software packages don't have the same variables. I was wondering how/where I can enter MV transformer losses. Apparently the "Transformer Losses" section is meant for the HV transformer at the substation.
SAM's Detailed PV model applies the transformer losses (no load and load) to the AC output of the inverter, so you could use it to represent any kind of loss between the inverter and grid interconnection point.