Life cycle impact of photovoltaic module degradation on energy and environmental metrics

Abstract

This paper presents the effect of photovoltaic (PV) module degradation on the cumulative energy demand and greenhouse gas emissions of a 4.2 kW dc roof-mounted grid-connected PV system. The estimated lifetime energy generation is coupled with life cycle assessment (LCA) as a way to evaluate the energy consumption and environmental impact. Three cases were evaluated; Case 1 considers the PV module degradation while assuming similar performance ratio (PR) for all conditions; Case 2 represents the most realistic case that considers the degradation and other factors affecting PR; and Case 3 serves as the worst-case scenario where the module degradation is neglected. Furthermore, four different types of PV modules were compared, i.e. mono-crystalline silicon, multi-crystalline silicon, cadmium telluride and copper indium selenide. In this work, system installations in five different countries from several regions were simulated. When applying the Cumulative Energy Demand 1.11 and Intergovernmental Panel on Climate Change 2013 methods, the cumulative energy demand and greenhouse gas emissions vary from 0.341 to 1.457 MJ/kWh and from 20.95 to 90.45 g CO2-eq/kWh respectively across different cases, PV module types and countries. It is found that neglecting the PV module degradation factor in performing LCA of PV system causes a significant underestimation. Also, PV module with a lower degradation rate showed low effect on the metrics. In addition, the metrics also vary with installations in different countries, mainly due to varying irradiation and ambient temperature factors.