Development and validation of a concise and anisotropic irradiance model for bifacial photovoltaic modules

The irradiance model is significant for accurately modelling the electrical and thermal performance of bifacial photovoltaic (bPV) modules, but existing irradiance models fail to be employed for bPV modules in a simple but reliable way. Therefore, this paper presented a concise and anisotropic irradiance model to predict the irradiance received by bPV modules, in which an improved view factor-based model was adopted to calculate the ground-reflected irradiance. In addition to its computational simplicity, the proposed model can satisfy the assumption of an anisotropic irradiance at both sides of the horizontal, tilted, and vertical bPV modules. Outdoor experiments were conducted to validate the proposed model under different conditions. Results show that the proposed model can well predict the irradiance of bPV modules placed above a concrete ground. The prediction errors of the front/rear/total irradiance are 7.1%/12.5%/6.1% and 11.9%/16.5%/8.7% for tilted and vertical bPV modules, respectively. In addition, the prediction performance decreases when a high-reflective ground made of aluminum foil is used. It is found that the albedo of the high-reflective ground will vary significantly on sunny days, mainly due to the incident-angle dependence of the ground reflection. Grounds with more diffuse reflections can improve the accuracy of the model's predictions.