Luminescence Measurements of PV Modules with a Cost-Effective and Small-Sized Hood-Based Tool under Daylight Conditions

We developed a small sized luminescence tool for photovoltaic (PV)-systems that can measure luminescence of a small part of a PV module. The tool measures the luminescence signal under maximum power point (mpp) conditions. For excitation of the solar cells 850 nm LEDs are used and the luminescence is measured with a small sized industry InGaAs camera. Furthermore, the tool detects a unique luminescence patter caused by the reverse current if the module substring has an electrically disconnected bypass diode. To the best of our knowledge, no other luminescence tool can detect this failure without changing the circuits of the PV system. The physical cause of this luminescence pattern is discussed in the paper. As the measurement procedure does not need any opening of electrical contacts it can be operated by any person with a short safety instruction. The paper describes the basic working principle of the measurement technique and simulations of the electrical circuit of the module are show. A 1.5 times higher excitation level in the hood relative to a 1000 W/m² sun irradiation stabilizes the working point to get reproducible luminescence images. During the measurement the inverter can work in normal mpp tracking mode and no access to the inverter is needed. The system is capable of performing measurements under daylight conditions and is sufficiently compact to be transported conveniently during travel. However, you need physical access to the modules to be tested.