3 years ago

Outdoor photoluminescence imaging of photovoltaic modules with sunlight excitation

Outdoor photoluminescence imaging of photovoltaic modules with sunlight excitation
Ziv Hameiri, Raghavi Bhoopathy, Mattias Juhl, Thorsten Trupke, Oliver Kunz
To operate photovoltaic power plants at maximum capacity, it is desirable to identify cell or module failures in the field at the earliest possible stage. Currently used field inspection methods cannot detect many of the electronic defects that can be revealed with luminescence-based techniques. In this work, photoluminescence images are acquired using the sun as the sole illumination source by separating the weak luminescence signal from the much stronger ambient sunlight signal. This is done by using an appropriate choice of optical filtering and modulation of the cells' bias between the normal operating point and open circuit condition. The switching is achieved by periodically changing the optical generation rate of at least one cell within the module. This changes the biasing condition of all other cells that are connected to the same bypass diode. This method has the advantage that it can deliver high quality images revealing electrical defects in individual cells and entire modules, without requiring any changes to the electrical connections of the photovoltaic system. High resolution outdoor photoluminescence image of photovoltaic module was obtained under full sunlight using contactless modulation method (Figure A) that can identify various defects that lead to power loss. This image was compared to the indoor electroluminescence image (Figure B). The contactless luminescence modulation is achieved by periodically changing the optical generation rate of at least one cell within the module, which in turn changes the biasing condition of all other cells that are connected to the same bypass diode.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/pip.2946

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