Evaluation of Photovoltaic Module Degradation Rates Under Tropical Climatic Conditions in Ibadan, Oyo State

Background: Long-term PV module degradation under Nigeria's tropical climate conditions affects energy yield projections and financial returns on solar investments. Empirically validated degradation rate data from Nigerian field installations are scarce. Aim: This study evaluated the degradation rates of photovoltaic modules under tropical climatic conditions at field installations in Ibadan, Oyo State, South West Nigeria. Methods: Current-voltage characteristic curves of 45 PV modules from three installations with service ages of 3, 7, and 12 years were measured using a solar module analyser. Degradation rates were calculated by comparing current parameters with nameplate specifications and correcting for irradiance and temperature conditions. Results: Mean annual degradation rates were 0.8%, 1.1%, and 1.7% for 3, 7, and 12-year-old systems respectively, with acceleration of degradation observed in older modules. Delamination, EVA discolouration, and corrosion of front contacts were the dominant failure modes. Modules from one manufacturer exhibited significantly higher degradation (2.3%/year). Conclusion: Tropical conditions accelerate PV degradation beyond standard temperate benchmarks. Nigerian buyers should require extended field performance warranties, and degradation rates of 1 to 1.5% per year should be used for financial modelling of solar investments. Keywords: PV degradation, solar modules, tropical climate, Ibadan, photovoltaic reliability.