Evaluation of a CdTe spectrally matched c-Si PV reference cell for outdoor applications

Spectrally matched PV reference devices can aid in performance monitoring of PV power plants by improving correlation between measured irradiance and system power output. For example, CdTe reference modules are widely deployed at First Solar power plants to serve as matched reference devices for CdTe installations. However, to complement the use of full-size reference modules, compact spectrally matched PV reference cells may also be desirable, because small form factor cells are more readily cleaned and/or heated by automated systems. Here we have evaluated a CdTe spectrally matched c-Si PV reference cell. The cell was designed with a filter specifically selected to minimize the relative impact of the cell to typical variations in solar spectrum due to atmospheric precipitable water vapor content, which is the most significant factor affecting CdTe spectral mismatch versus c-Si. We review the design of the cell and the filter selection and present evaluation data comparing the cell's performance versus CdTe reference modules under a range of outdoor conditions. The results indicate a good correlation between measurements from the filtered cell versus the CdTe modules under varying spectral content and under both diffuse and direct light. We discuss the potential implications for use in CdTe PV power plant monitoring.