Connecting photovoltaic cells to form an array IN TROD UCTIONhotovoltaic (PV) cells have been developed to the point where they are viable for a range of applications. However, a major problem still affecting the performance and reliability of PV P systems is that of mismatch. Mismatch occurs due to the interconnection of cells with different performance characteristics. This condition results in two detrimental effects: power loss and reliability degradation.When the characteristics of cells within a PV array differ, individual cells may operate suboptimally, causing a reduction in array output power. This is especially the case for cells connected in series with variations in their current outputs. Such a situation may arise simply through shading of a single cell through leaves, bird droppings or dirt falling onto the array. '-' ' Figure 1 shows a typical example of mismatch where a single low current output cell (caused by, say, partial shading) is series connected with four identical cells having normal current outputs. The resultant current-voltage ( I -V ) relationship shows that the current output of the shaded cell significantly limits the current and hence power output of the array. In extreme cases, almost the entire array output can be lost through shading of a single cell. Furthermore, when the array in Figure 1 is short circuited, the low current output cell is severely reverse biased whilst the other cells operate near their maximum

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