Flash Testing and Binning of Solar Cells: Sorting Cells by Power

… more less Flash testing and binning is the last step of the cell line. Every finished cell gets measured before it goes into a panel. A lamp gives a bright flash, matched to standard sunlight, for a few thousandths of a second. The flash is short so the cell does not heat up. During it, a meter sweeps the voltage and records the current. That gives the cell's J-V curve. From it, the tester reads short-circuit current, open-circuit voltage, fill factor and power. A camera often checks the cell for cracks at the same time. Cells are then sorted into bins by power and current. Bins are narrow steps, so cells in one module match closely. This matters because cells in a string are wired in series. The string can carry no more current than its weakest cell, so one low cell drags down the rest. Matched cells waste less power. Binning also explains the power classes on a data sheet, such as 400, 405 or 410 watts. Cells that are cracked or far below spec are rejected. Some are sold as lower grades. Others become scrap that is crushed for its silicon and silver. Good process control keeps that scrap small, which saves all the energy already spent on the wafer. After this Concept you can explain why a panel's cells must match, and read the power class and tolerance on a module data sheet.