PV makers, test labs develop PID-effect module test

SCHOTT Solar AG, Q-Cells SE, Solon SE, Fraunhofer ISE, PI-Berlin, TÜV Rheinland Energie und Umwelt and VDE Prüf- und Zertifizierungsinstitut have developed a method to test potential induced degradation (PID) in the solar module manufacturing process.

September 8, 2011 — SCHOTT Solar AG, in collaboration with Q-Cells SE and Solon SE and the independent test laboratories Fraunhofer-Institute for Solar Energy Systems (ISE), Photovoltaic Institute Berlin AG (PI-Berlin), TÜV Rheinland Energie und Umwelt GmbH (TÜV) and VDE Prüf- und Zertifizierungsinstitut (VDE), have developed a method to test potential induced degradation (PID) in the solar module manufacturing process.

PID is a performance degradation caused by high negative voltage. The PID effect can occur with all crystalline silicon solar cells that are embedded in glass-foil modules. Leakage currents can result under unfavorable conditions (accelerated by high humidity and temperatures) where the module joins with the frame and causes short circuits that lower the overall performance of the system. With the so-called double glass modules, this effect manifests itself to a significantly lower extent from the very beginning. It can be avoided at the system level if the system is grounded or inverters that do not generate negative voltages are used. However, it is more economical to prevent PID at the module or cell level.

The test conditions call for modules from the current production series to be connected to voltage of -1,000V for 7 days. In order to be able to obtain exact comparison values, all of the modules are covered with aluminum foil and tested at a constant temperature of 25°C. A module is considered to be PID resistant if it loses less than 5% of its nominal capacity during this period.

The test series performed by several independent test laboratories revealed that glass-foil modules from SCHOTT Solar and moduels from Q-Cells and Solon passed the PID test. Several of the modules from other brand-name manufacturers experienced drops in performance well in excess of 50%.

The test quickly and clearly demonstrates a crystalline module’s stability under PID conditions, the companies report. Further development of the test conditions will be undertaken with the IEC TC82 standardization body, aiming for assessments under exact connections and climatic conditions.

SCHOTT Solar is an integrated manufacturer of crystalline silicon wafers, cells and modules. The company also supplies thin-film technology and receivers for solar power plants. Learn more at www.schottsolar.de.

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