The operation of loads powered by separate sources or by a common source of solar cells

In many photovoltaic systems, the solar cell array is designed to power a specific single load. Several loads of the same or different types may be powered either by separate solar cell sources for each one, or alternatively, by a common solar cell source for all the loads; and for each one of these two possibilities, the system may include a maximum power point-tracker (MPPT). The purpose of this paper is to introduce a procedure for comparing the performance of these two possible setups. The operation of loads of the same type and the same size perform the same when powered either by separate or by common sources of solar cells. Loads of different sizes, either of the same or different types, that are connected to a common source interact with each other so that one load may improve its operation at the expense of another load. It is also possible that the total performance of the loads in a common source system is improved as compared to the total performance of the loads when they are powered separately by individual sources; the designer of a photovoltaic system may wish to analyze this possibility. In a common source system there exists also an additional option where, in certain cases, it might be advantageous to disconnect a load from the system in order to improve the operation of another load. The criterion used for comparing the performance of the loads was the “energy utilization efficiency”. Two types of loads were considered as examples: (a) two different ohmic loads; and (b) two different water electrolyzer loads. The study shows: the performance of one load affects the performance of another load in a common source system; in systems not including MPPTs, the total performace of the loads in a common source system is improved as compared to the total performance of the loads when they are powered separately by individual sources; in systems including MPPTs, the total performance of the loads is the same when powered either by a common source or by single sources; and MPPTs improve the performance of loads, the amount depending on the mismatch of the loads to the solar cells.