Figure 5: Histogram of the deviation from the average
photogeneration in the inhomogeneity map shown in Fig.4 (+/- 0.4%
inhomogeneity case). In our data set, the photogeneration deviations for
each category are a single value (the value shown on the horizontal
axis), and not a continuous spread.
It can be seen from Fig. 4 that the average values, and also the minimum
and maximum values of the three strings, are very similar. It can
therefore be expected that the bypass diodes will have only a minor
effect on the I -V curves, which is also what we found in
our simulations. However, in an inhomogeneity scenario, individual cells
will be forced into reverse bias along the lower voltage range of theI -V curves, also in the presence of bypass diodes. We
therefore have to consider the reverse-bias characteristics of the
individual cells when exploring the effects ofI PH inhomogeneity.
Clement et al . [8] published reverse-bias characteristics for
different solar cell technologies, and Fig. 6 shows as curve in red
(case 1, labelled “IBC homojunction”) a digitized version of the
reverse bias characteristics published by Clement et al . for IBC
cells.
Case 3, the black curve in Fig. 4 is the simplest case, using for
forward and reverse characteristics the sameR Shunt resistance (see also Table I with the
standard parameter set used in this study).
The blue curve, i.e. case 2, uses also the sameR Shunt in forward and reverse characteristics,
but in combination with an added “softened break-through” compared to
the “IBC homojunction” of case 1. This break-through