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LED-based differential spectral responsivity measurements of PV modules


Spectral responsivity (SR) measurements are a powerful technique to measure the opto-electronic properties of photovoltaic devices like solar cells or PV modules. Although the SR determination of solar cells is a common and established technique for many years, much more effort must be taken to determine the SR of PV modules due to their size. Significantly larger and more complex solar simulator must be used, which led to a variety of different measurement techniques, each with its own disadvantages. In this work we present SR and linearity measurements performed with an LED-based solar simulator, which is capable of measuring the SR of a whole PV module within a reasonable amount of time. The principal solar simulator characteristics with its advantages and challenges are presented, including the properties of the emitted spectrum and the homogeneity of the resulting light field. The evaluation of our method, which is performed at conditions close to standard test conditions (STC) and bears characteristics of a differential spectral responsivity (DSR), is presented and demonstrated on different silicon-based and thin film PV modules, respectively. With the ability to tune the spectral irradiance gradually while maintaining an AM1.5g-like spectrum, linearity measurements of the short-circuit current of PV modules have been performed and are presented as well.

Figure 1: Normalized DSR of two different mc-Si modules with calibrated SR measurements performed at the Fraunhofer ISE CalLab (full lines). The deviation of both measurements is denoted by the dashed lines.



Hendrik Sträter *1, Stefan Riechelmann *1, Frank Neuberger *2 and Stefan Winter *1
*1 Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany
*2 Fraunhofer Institute for Solar Energy Systems (ISE), Heidenhofstraße 2, 79110 Freiburg, Germany