Solar Cells Failure Modes and Improvement of Reverse Characteristics
The growing number of large photovoltaic installations calls attention to the possible development of “hot spots” leading to a loss of power in the best case. Catastrophic consequences on the whole array can be avoided by particular precautions taken at the cell, panel and system design level. Hot spots problems arise in modules when one or several cells become back biased and operate in the negative voltage quadrant, as a result of short-circuit current mismatch, cell cracking or shadowing.Optimization of system designs with diodes protections has already been demonstrated by France-Photon in a previous paper(l). Further to the industrialised matching of the cells in a same module, an important result of this study is that we can improve the capability of dissipating reverse power by decreasing the shunt resistance with negligible sacrifice of the direct peak power. After a complete study of the dark direct current, we show for our basic technology that the main parameter which governs the slope of the reverse characteristic is the shunt resistance and we indicate trends to understand its fondamental causes and their relative weight for single and semicrystalline cells.
KeywordsNIckel Furnace Convection Recombination washIng
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