Towards a higher power, all LED solar simulator closely matching realistic solar spectra

Photovoltaic devices increase in complexity and thus introduce new calibration challenges, largely being affected by deviations of test spectrum from natural spectra. Future energy rating standards will impose further challenges as one needs to simulate realistic sunlight spectra conditions. Generally only light intensity and module temperature can be varied in a solar simulator, which means that they do not provide the variability of environmental conditions and it maintains problematic to measure multi-junction solar cells. A solution to this is to use LEDs instead of the traditional light source in a simulator. Their unique characteristics allow precise intensity adjustment and the combination of a steady state with a flash solar simulator, thus providing high flexibility. With the LEDs availability in colours over the whole spectrum, the AM1.5G spectrum can be accurately represented with the benefit of an adjustable spectral output. CREST has designed and constructed an LED-based solar simulator prototype of which the hardware set-up as well as classification results and PV device and repeatability measurements are presented. Weaknesses of the prototype and their solutions have been indentified, and are currently being realised in the next stage of the development. Those are described in detail.