Performance evaluation of solar irradiance transposition models and seasonal tilt angle optimisation using long-term data in a semiarid climate

Solar photovoltaic systems are at the forefront of driving India toward a renewable-based economy, especially in arid or semiarid regions with high solar potential, like Kota, Rajasthan, which still faces seasonal challenges due to dust, monsoon cloud cover, and fluctuating solar angles. This study evaluates various well-known transposition models, namely Liu-Jordan, Hay, Klucher, Reindl, Hay-Davies-Klucher-Reindl, and Perez, for estimating global tilted irradiance as well as determining optimum tilt angles for photovoltaic installations using 16 years of Photovoltaic Geographical Information System data over Kota, Rajasthan. Monthly and seasonal analyses have been carried out, while the model evaluation has been quantified in terms of root mean square error and mean bias error. The results indicated that, out of all the evaluated models, the Perez model exhibited the best performance, with the least root mean square error and an mean bias error close to zero, hence having a high degree of accuracy under the diffuse and anisotropic sky conditions of the study area. The optimal tilt angles obtained using the Perez model varied seasonally, varying from 6.74° during the monsoon period to 51.54° during winter, while the annual optimum was close to 26.03°. Seasonal increases in global tilted irradiance were maximum during winter and post-monsoon seasons at around 9.18 and 4.22 kWh/m², respectively, which corresponds to an irradiance gain of about 7–8% at a fixed tilt of 25°. Then, the energy yield and environmental benefits using optimised irradiance values for a 1 kW PV system have been estimated. The results of the analysis revealed that an improved annual energy yield of 20.91 kWh/m², equivalent to an increase of 6.43% compared to the standard fixed tilt setup, could be realised. Besides, this optimised tilt configuration results in an annual reduction of about 15.20 kg/m² of CO₂ emissions, reflecting its suitability to enhance the performance of photovoltaic systems in Kota's climatic conditions. As a whole, the calculations demonstrated that highly accurate estimates of global tilted irradiance result in maximum energy output with environmental benefits using the Perez model. These findings provide useful information for solar system design and climate adaptation in general and on the robustness of the model within semiarid environments.