Impact of Bifacial Illumination and Sorting Criteria of Bifacial Solar Cells on Module Power
As the market share of bifacial cells and modules grows, solar cells measurements under bifacial illumination are increasingly becoming a focus of interest. In this work, we present an analysis of four different sorting criteria for bifacial solar cells with the aim of evaluating the impact of these criteria on the power of the modules assembled with the sorted cells. First, we develop a simulation model for bifacial modules based on the two-diode model. Secondly, we generate a representative virtual data bank made up of 50000 cells, whose parameters are determined in account with empirical parameter distributions measured on a group of 300 bifacial solar cells with passivated emitter and rear (PERC) manufactured industrially. Third, we sort and bin all cells according to the current density under front illumination at maximum power point (MPP) (jmppfront). Fourth, we assemble modules from all bins, calculate the module power under bifacial illumination for five different scenarios with varied front and rear irradiation and evaluate the average module power as well as the distribution of module power. The sorting of the cells (3rd step) and the calculation of the module power (4th step) are repeated for sorting the cells according to the current at MPP under bifacial illumination (jmppbi) and the maximum power under front only and bifacial illumination (pmppfront and pmppbi). With respect to the average module power, a very small gain of less than 2 W (in the most extreme illumination scenario) can be achieved if a bifacial instead of a monofacial sorting parameter is taken as sorting criterion. However, a strong effect on the distribution of the module power is manifested, obtaining either one homogeneous group of modules with broad power distribution or several classes/bins of modules, depending of the cell sorting criterion. Therefore, the choice of the sorting criteria of the cells depends on the interest of the solar manufacturers and has a great potential to reduce module mismatch in PV arrays.