Long-wavelength infrared optical properties of polycrystalline silicon PV modules under clean and soiled conditions for thermography analysis

Despite advances in photovoltaic (PV) technologies, polycrystalline silicon (poly-Si) modules remain important in countries that have experienced significant solar growth over the past decade. Thermography is widely used for inspecting PV modules in large-scale solar parks, facilitating the detection of thermal faults. However, limitations such as viewing angle and soiling can affect measurements and decision-making processes. This study investigates the directional emissivity and reflectivity of a poly-Si module under clean and contaminated conditions, using both urban and mineral dirt. A custom experimental setup enabled thermographic inspections using a FLIR SC660 thermal camera across a range of viewing angles (0°to 70°) and temperatures (25 °C to 60 °C). The results demonstrate that emissivity decreases and reflectivity increases with larger viewing angles, with surface temperature exerting minimal impact. Soiling made the surface less reflective, with overall optical trends remaining consistent. These findings contribute to existing literature by addressing the gap in available data on the directional optical properties of poly-Si modules. The results have practical implications for thermal inspections, emphasizing the importance of viewing angles in data interpretation and suggesting adjustments to enhance the rigor of assessments. By providing experimentally derived optical property values, this study also supports the correct application of quantitative thermography in solar plant monitoring.