The transmission level of the incident light on the photovoltaic (PV) modules depends on the angle of incidence (AOI)
and air/superstrate interface. The AOI dependence for the air/glass interface has already been well established. When the
glass superstrate is covered by a soil/dust layer, the air/glass interface is altered and thereby changes the AOI dependence
to air/soil/glass interface. In this work, PV modules retrieved from the field that had different dust densities have been
measured for the dependence of the AOI curves on the dust gravimetric densities. It was determined that the AOI curve
is inversely related to the soil density. The critical AOI for the air/glass interface is about 57° and it shifts dramatically as
the soil gravimetric density (g/m2) increases. The measured AOI curves were then fitted and validated with the
analytical/empirical models reported in the literature.