Energy Yield Model for Bifacial PV Systems: A study and analysis of temperature & rear irradiance models

Abstract

In order to make the bifacial yield prediction models commercially available, a lot of work their development, improvement and validation is being done by many research institutes. At Energy research center of the Netherlands (ECN), one such model is under development. In this project, couple of aspects were investigated to give better insight into improving the model. The two main aspects of the model that were investigated were the rear irradiance estimation and the temperature prediction of the model.
Analysis of rear irradiance aspect of the bifacial yield model through simulations at low tilt angles and elevations should in practice result low rear irradiance but the results showed the opposite. From the literature, a new factor called acceptance was implemented in the rear irradiance model which led to correction in estimation of rear irradiance. For the temperature model, initially indoor measurements of three laminates of bifacial cells and three laminates of monofacial cells were performed under solar simulator. The experiment resulted in finding differences in measured and cell temperatures for all six laminates. According to measured temperatures, the bifacial cell laminates were hotter than their monofacial counterparts, which may not be correct due to higher absorption of irradiance by backsheets in bifacial cell laminates. The differences in calculated cell temperature and measured temperature were investigated and were found to be different. The heating behavior of all laminates was modelled and heat capacity and heat transfer coefficient found through modelling were found to be in good agreement with literature values. Outdoor measurements were used for temperature analysis of bifacial panels and again the differences in calculated cell temperature and measured temperature were found. Non-steady state temperature model was found to be more accurate for low resolution meteorological and insolation data of less than ten minutes as compared to the steady state model used by current ECN model. The difference between measured and cell temperature was translated in terms of heat transfer coefficient and for this difference, the annual energy yield results showed a variation of 1.45 %.
The results of the project showed improvement of the bifacial yield model by ECN through an improved rear irradiance estimation. Furthermore, non-steady model should be used in case the input meteorological and insolation data is in less than ten-minute interval.