Modeling of annual DC energy losses due to off maximum power point operation in PV arrays

This paper describes a straightforward methodology for modeling photovoltaic arrays comprised of variously configured sub-arrays connected to a single inverter. Particularly in rooftop applications, PV arrays must be installed within the constraints of various roof slopes and geometries. This reality calls into question the typical modeling assumption that each panel operates at its maximum power point, even when shading effects are ignored. A series of scenarios are presented with a variety of array orientations, string configurations, and temperature effects. Each scenario is modeled in detail using industry standard modeling tools, and the operation characteristics and DC losses due to sub-array layout mismatch are presented. Typical losses resulting from sub-optimal relative alignment of fixed array layouts are on the order of a one percent or less on an annual basis, suggesting that sub-array orientation in the absence of shading is not a major factor in small to medium scale system energy yield.