1. If a solar cell is shaded by a tree, a building or module dust, its output declines. If there is no bypass diode, the shading of one cell causes the current in the whole string to fall to the level of the shaded cell.
2. Shading is one of the most significant causes of losses in a pv system. There are several technical solutions to avoid shading losses. Nevertheless the best solution is to evade any partial shading when possible.
PV cell losses
http://www.pveducation.org/pvcdrom/modules/shading (1.); http://www.greenrhinoenergy.com/solar/performance/shading.php (2.)
Author: Svenja Gutt