Modelling shading on amorphous silicon single and double junction modules

The effect of shading amorphous silicon mini-modules is investigated by means of measurements and simulation. Several devices are measured under varying degrees of shading and the reverse bias behaviour is investigated, including the reverse breakdown voltage. A simulation using a modified single diode model for amorphous silicon is presented, in which the Bishop extension of the shunt resistance is used to simulate the behaviour of shaded devices. The differences between the effect of shading on amorphous silicon and on crystalline silicon devices are investigated based on measurements and simulations. It is shown that the thin film cells do not develop hot spots in the same manner as crystalline silicon devices; they always break down at the interconnection to the adjacent cell.