pvPlanner shows energy output for optimally sized PV system. Potential losses that may result because of oversizing or undersizing of the array are not considered.
However, we plan to implement very soon the possibility to allow input of inverter efficiency curve, which would allow the user to input inverter efficiency for different rated powers of the inverter. This feature is already implemented in pvSpot and allows us to calculate losses because of oversizing or undersizing of the array.