Figure 6: Reverse-characteristics of cell I -V curves used in the simulations in this paper for modules withI SC-mismatched cells.
characteristics of the case 2 blue curve is approximately identical to a 3-fold increase of the reverse break-through reported by Clementet al. [8] for PERC solar cells under 1-Sun illumination intensity.
The yellow curve in Fig. 6, i.e. case 4, uses in reverse direction a three-times higher shunt resistance than in forward direction. Neither cases 3 nor 4 feature a reverse breakthrough and have only a linear reverse-bias characteristics. While a real solar cell does have a break-through at some reverse-bias voltage, these purely linear reverse bias cases can be regarded as cases representing cells with a very high break-through voltage.
3 RESULTS
3.1 I SC-matched cells
For a scenario of I SC matched cells we have to consider only the parameters I 0, n ,R Sh and R S, becauseI PH is virtually identical toI SC for all practical scenarios that we need to consider here. Variations of the series resistanceR S amongst the cells do not cause effects that would be misinterpreted as an intensity dependent shunt. This can be easily understood by noting that the individual series connected elements of the string circuits in Fig. 3 can be regrouped, such that all series resistances of the individual cells are placed on one end of the re-grouped string circuit, and all diode-containing elements on the other end. In other words, all series resistances can be lumped together into one big resistance, and its effect does not depend on the distribution of individual cell R S values that the lumped big series resistance originated from.
It is therefore of bigger interest to examine what effect have distributions of I 0 values, ideality factor values n , and distributions of shunt valuesR Sh.
In a voltage range where the exponential part of equation 1 dominates the current for all cells, we can approximate and re-write equation 1 for all cells as: