All photovoltaic (PV) arrays are, at times, shaded. Almost all lose energy from shading at rates that are larger than the simple portion of the array that is shaded. The cumulative effect of each day’s and each season’s changing shade patterns will typically reduce annual energy production by a financially significant 2-5%. All PV modules are rectangular. Almost all have lengths twice their widths, for an aspect ratio of 2:1. Should a module be mounted in landscape or portrait? Should its wires connect to the next one above, or the next one over? Does either the mounting direction or the wiring direction affect shading losses? If so, there are four possible ways to mount and wire an array. Which is the best combination? This paper discusses why PV arrays lose more energy than expected due to shading, and explores what can be done about it in terms of layout options.
Shading loss for common photovoltaic array layouts - white paper