Spectrally-resolved optical efficiency using a multi-junction cell as light sensor: Application cases

The experimental method to determine the spectrally-resolved optical efficiency of concentrating optics is described in this paper. The measurement uses a multi-junction solar cell as light sensor and a series of band-pass filters to isolate the optical performance of different narrow spectral bands throughout the spectrum of interest. Additional bias light is provided to saturate the subcells whose spectral response is out of the transmittance of every band-pass filter. The method allows the characterization of the combined transmittance, reflectance and absorbance of every material composing the optics including optical couplers and thin layers such as antireflective coatings. The two application cases included illustrate the potential of this novel characterization technique. Firstly, a novel refractive concentrator, the Achromatic Doublet on Glass (ADG) Fresnel lens is measured. Secondly, the method is applied to analyze the degradation of outdoor exposed glass molded Secondary Optical Elements (SOE).