PID resistance of Panasonic HIT PV modules confirmed by Fraunhofer

JAPAN: Panasonic Corp. announced that the resistance to potential induced degradation (PID) of its HIT photovoltaic modules has been confirmed by the Fraunhofer Center for Silicon-Photovoltaics (CSP).

PID is a phenomenon in which the power output of photovoltaic modules is reduced when they are subjected to external factors, such as high temperatures and humidity, under conditions where a high voltage is applied across the internal circuits (photovoltaic cells) and the grounded frame.

HIT photovoltaic modules are renowned for their outstanding performance and quality. Due to the special HIT structure, which refers to a thin mono crystalline n-type silicon wafer surrounded by ultra-thin amorphous silicon layers, the modules have a high efficiency.

With respect to conventional crystalline silicon-based photovoltaic cells, the accumulation of electric charges near the insulating layer on a cell surface is thought to be a direct cause of PID. However, in the case of HIT photovoltaic cells, both surfaces are transparent conductive layers with no insulating layers used. Therefore, no PID is thought to occur. No incidences of PID have been reported from the European, US, or Japanese markets.

In collaboration with Fraunhofer CSP, Panasonic set up a test that included both negative and positive voltages. During the test, the HIT modules were subjected to 1,000 volts for 48 hours at a temperature of 50 degrees Celsius with 50 percent relative humidity. The Panasonic HIT photovoltaic modules exhibited no sign of degradation under such conditions. Of the ten modules used for the test, five were subjected to +1,000 volts, and the other five to -1,000 volts over 48 hours. The results show no evidence of PID.

Michael Seys, in charge of photovoltaic product development of Panasonic Eco Solutions Energy Management Europe, stressed, "Since HIT modules have been proven to be PID resistant by one of the most authorized agencies in the field, our customers can now be fully assured that our modules deliver an excellent performance."

Dr. Matthias Ebert, Head of the Group Module Reliability at Fraunhofer CSP, commented on the test results: "HIT modules differ from standard modules. The challenge for us was to develop a test method that would respect this. By testing for both positively and negatively charged voltages, we can attest to the PID resistance of HIT photovoltaic modules."

Panasonic intends to accelerate the development and commercialization of high quality and highly reliable photovoltaic cells and to work on expanding this business globally.