The effect of interconnection and bypass diodes on the reliability of photovoltaic modules and arrays have been evaluated. Analysis of different cell or panel interconnections for the determination of the optimum item configuration and circuit design strategies to achieve reliable modules and arrays has been carried out. A computer program for finding the optimum configuration which produce maximum module and array reliability is presented. The roll of bypass diodes for module and array reliability improvements have been studied theoretically and experimentally. It is found that module and array reliability depends on the item's (cells or panels) probability of failure, arrangement of the items, and failure mode. Discussion and suggestions for optimum design are presented.