Assessing Methods for Potential Induced Degradation in Photovoltaic Systems

The paper presents some studies focused on a problem that has gained great importance in recent years: the so called potential induced degradation (PID) on poly-crystalline and mono-crystalline solar modules.Since the potential induced degradation on solar modules is very gradual, it is difficult to highlight or localize it, even if monitoring is daily performed by using a data logger, evaluating and comparing the results. The main reason for not recognizing the PID effect from the very beginning is the daily difference regarding the solar radiation.The five most used methods of PID detection are briefly reviewed, being identified strong points but also the limitations of each of them. The investigated methods are the following: the measurement of the current power of a module or a string, the examination of infrared radiation by means of thermography, the determination of UV fluorescence, the measurement of electroluminescence process by using special cameras and the evaluation of dark characteristics and/or bypass diode check.Furthermore, through our researches on the domain of photovoltaic systems, we were able to recognize that PID on solar power modules appeared more in wet weather and rain over a longer period of time than during rather dry weather periods. It indicates that PID is more recognizable after the autumn and winter period than after summer months.Finally it is proposed a regeneration of PID by generating reverse currents at night.