Evaluation of locally available materials as thermal insulators for PV modules

The operating temperature of photovoltaic (PV) modules has a pronounced influence on electrical efficiency and long-term reliability, particularly in tropical regions characterized by high ambient temperatures and intense solar irradiance. This study investigates the suitability of selected locally available agricultural and bio-based materials as backside thermal insulators for PV modules, with the aim of providing a low-cost and sustainable alternative to conventional synthetic insulation. Rice husks, sawdust, banana fiber derived from banana pseudostems, coffee husks, and a clay-straw composite were experimentally evaluated and compared with a polystyrene insulation board and an uninsulated baseline. Outdoor experiments were conducted using seven identical 100 W polycrystalline PV module under open-sky conditions in Kampala, Uganda, with measurements recorded at 15-min intervals between 10:00 a.m. and 3:00 p.m. over a 3-month period. Thermal conductivity was determined using standardized laboratory methods, while module operating temperature and electrical performance were monitored in situ. The results show that all locally sourced materials reduced module operating temperature relative to the uninsulated case, with rice husks and sawdust achieving the greatest reductions of up to 7-9 °C and corresponding electrical efficiency improvements of up to 5% during peak irradiance periods. One-way ANOVA and Tukey HSD post-hoc analysis confirmed statistically significant differences among insulation materials (p < 0.001). The findings demonstrate that agricultural waste materials can effectively enhance PV module performance under tropical conditions, offering a cost-effective, environmentally sustainable, and locally adaptable approach to passive thermal management for solar energy systems in developing regions.