Diagnosis of a Power Output Lowering of PV Array with a (-dI/dV)-V Characteristic

It is reported that the volume of an estimated PV system installations in Japan must be set at about 4.82 [GW] up to 2010. As a result, it seems that PV systems must spread in the future in a general household, and therefore the maintenance and management of PV systems must become important keeping to the normal output performance of a PV system. However, it will be very difficult to locate the lowering factors to affect to output performance of the PV system installed in a residential rooftop. Besides, even if a cause of the output lowering of the PV system was found more, it will be very difficult to remove these. The authors paid attention to that shape of an I-V characteristic of a PV system changed by the output lowering caused by loss factors such as deterioration of a PV module, a shadow, and so on, and study the method to simply and automatically evaluate the output lowering of a PV system. In this paper, the (dI/dV)-V characteristic to be obtained from the I-V characteristic of a PV array is adopted as the standard characteristic for the automatic analysis. The (dI/dV)-V characteristic was simulated with an abnormal I-V characteristic of PV array covered in a shadow partially. A performance fall of PV array to be caused by a partial shadow is evaluated by an appearance of a peak of the (dI/dV)-V characteristic, and an appearance position of this peak changes by a condition of a shadow. From these results, it became clear that an appearance of a peak of a (dI/dV)-V characteristic must be means to be effective to diagnose the output lowering of a PV system