Spatially-resolved modelling of dust effect on cadmium telluride photovoltaic modules

Abstract

A spatially-resolved 3 dimensional model is developed utilising the circuit analysis software PSPICE to investigate the effect of inhomogeneously deposited dust on the performance of Cadmium–Telluride photovoltaic (PV) thin film modules. CdTe devices are wide band gap materials and typically have a non-ohmic back contact, which are major differences to other technologies which might impact of the effects of dust on device performance. The effects of dust concentration and tilt angle on the PV module’s performance are investigated by simulating the effect of patterns created on the module’s surface during long- and short-term exposure. This deposition is inhomogeneous and it is shown that severe localised mismatch can occur. The PSPICE model is then used to investigate the likelihood of localised hot-spot formation in different installation orientations. The model crucially considers the impact of dust on the spectrum seen by the PV module, which is shown to be critical when modelling the performance of wide band-gap devices such as CdTe. It is shown that performance continuously deteriorates with increasing dust concentration, with operating efficiencies decreasing by 34% in only 90days. The tilt angle of the installation will have a significant effect on the overall dust accumulation, which, as shown in the paper, will change over time. It is shown that the module orientation impacts on the risk of hot-spot formation and the worst case for this is a horizontal orientation of the devices. The non-ohmic back contact of the Cadmium–Telluride modules does not appear to increase the risk of hot-spot formation in comparison to ‘normal’ back contacts.