Shading and masking affect the performance of photovoltaic systems-a review

Photovoltaic collectors in the second and in the subsequent rows in a multiple row deployment of PV fields are subject to two effects: Shading and masking both of which reduce the incident solar radiation, and hence reduce the electric energy generated by the PV field. Shading affects the direct beam incident radiation and masking (expressed by the sky view factor) affects the diffuse incident radiation on the PV modules. Both effects depend on field and collector geometric parameters. The result of these effects is uneven distribution of the incident solar radiation on the PV modules, manifested by formation of steps across the I-V characteristic. However, these two effects differ in their nature-shading depends on the movement of the sum and is time dependent whereas masking is position dependent and attains constant values, dependent on geometrical parameters only. Not much attention was paid in the past to the masking phenomenon and its effect on the power loss of PV systems. A series of recent works show that masking in PV fields is an emerging topic of technical significance. Masking may be more detrimental than shading, especially at locations with high percentage of diffuse radiation.