A modelling approach for long-term degradation of thin film silicon photovoltaic modules

This paper introduces a new concept of approach for modelling the ageing behaviour of a-Si PV modules with voltage-dependent photocurrent. The basis is the equivalent circuit of a PV module, specifically the modified single diode model. The parameters are extracted from I-V measurements. Ageing is then analysed by relating these to the environmental stresses seen by the devices. This paper focuses on the behaviour the product of carrier mobility and carrier life time (μτ), since the μτ has been considered to be an important indicator for module degradation of amorphous silicon thin film devices. A fitting approach for determining μτ is discussed and extended to be applied to the outdoor module IV data. Three a-Si modules of the same type operating under different temperature conditions are analysed to identify changes in the μT.