Fraunhofer CSP presents results of potential induced degradation (PID)
Fraunhofer Center for Silicon Photovoltaics CSP
Halle, June 11th 2012 - In the last years degradations of crystalline silicon solar modules were observed in installations if the cell polarized with a negative voltage bias. This occurs if transformerless inverters are used. The effect was called potential induced degradation (PID).
The Fraunhofer Center for Silicon Photovoltaics CSP has performed an accelerated high voltage test to characterize the PID susceptibility of commercial solar modules. In the test the temperature (+50 °C) and the relative humidity (50 %) was increased thus the test duration was decreased to 48 h. A negative voltage bias of -1000 V was applied. The modules were covered with a thin aluminum foil on the glass side to generate a homogeneous electric filed.
The module power of the solar modules was measure before and after the test under STC. In investigation included 13 commercial solar modules from various manufactures, mainly from Europe and Asia with sixty 6’’ solar cells. The table below shows the tested modules. The figure shows the relative remaining power after the test. Only 4 out of the 13 modules showed no degradation.
Professor Jörg Bagdahn, director of Fraunhofer CSP, said: » We were surprised that so many modules showed such a high degradation. A few manufacturers have found a solution for their products, in contrast the degradation is striking for the majority of the tested modules. We have provided the test results to all companies for further discussions«. Dr. Matthias Ebert, head of the group module reliability, added: » Our applied accelerated test conditions are below the test conditions which are currently discussed in the new IEC standard (60°C, 85 % rel. humidity, -1000 V ???). It is essential to define test standards to avoid long term failures with not PID resistant modules. In current research projects at Fraunhofer CSP we develop solutions to avoid the degradation effect«.
Solar module of the following companies were tested (in alphabetic order): Canadian Solar Inc., Kyocera Solar, LG Electronics, LUXOR Solar GmbH, Q-Cells SE, REC Solar, SCHOTT Solar AG, S-Energy, Sharp Solar, Solarwatt AG, Suntech Power, Trinasolar, Yingli Green Energy Holding Co., Ltd.
A detailed technical presentation of the test will be available at the booth of the Fraunhofer CSP (A 6.170).