Figure 4: Inhomogeneity map [in “% of average”] of the photogeneration J PH used for the simulation of modules with I SC-mismatched cells. The 6 x 10 distribution in the upper schematic is taken from a subset of the intensity data map of the paper of Ramspeck [6]. The lower schematic lists minimum, average and maximum photogeneration in the cells of the three different cell strings in the module, and it additionally serves as color scale for upper schematic with the +/- 0.4% inhomogeneity case shown here.
In case of completely identical cells in the module, the illumination intensity map in Fig. 4 translates directly into an identicalI PH photogeneration map. It therefore describes the best expectable I SC inhomogeneity distribution, limited only by the illumination inhomogeneity of a state-of-the-art module flash tester.
We will also explore the effect of larger inhomogeneities, by usingI PH maps that are scaled from the +/- 0.4% inhomogeneous map of Fig. 4 to inhomogeneities of +/- 1.0% and +/- 2.0%. These larger inhomogeneities can be understood as either representing measurements with a less ideal module flash tester, or representing I PH inhomogeneity distributions originating from a combination of cell production quality variation in with an illumination area inhomogeneity.
Note that our inhomogeneity map consists of only seven different values, as is shown in the histogram in Fig. 5 for the +/- 0.4% inhomogeneity case. Our cases of increased inhomogeneity only spread these seven values over a larger minimum-to-maximum range. These maps are therefore only a rough representation of a real-world inhomogeneity distribution but will serve sufficiently well to show the fundamental effects of inhomogeneity.