On the historical origins of bifacial PV modelling

This paper recounts an historical record of the origins of bifacial PV modelling in the years between 1983 and 1989. Associated to the first industrial production of bifacial PV modules, that took place in 1984, PV modelling was developed by completing the three stages of an engineering modelling path: model development, experimental validation and application in practical designs. This took place over two distinguishable stages. In the first stage, the mathematical foundations, based on the “view factor” concept and an application procedure, based on calculating the so-called albedo and sky maps were established and applied to the PV generators with only a ground reflector surface. In the second stage, an additional mathematical twist lead to solving the problem of multiple reflector surfaces, and different practical configurations were analyzed. As PV modules were expensive at that time, it was economically sensible to consider PV arrays made up of rows of modules with a module-to-module separation between the modules of the same row. That led to the development of 3D models. Experimental values of rear irradiance were compared with modeled ones, using the global horizontal irradiance and direct irradiance values given by a pyranometer and a pyrheliometer respectively as input. The theoretical ratio between the daily front and rear irradiations was within 3% of the determined experimental value. This is the same as the accuracy in standard tilted surface irradiation predictions.