Optical cell temperature measurements of multiple CPV technologies in outdoor conditions

Abstract

It is well known that photovoltaic performance is dependent on cell temperature. Although various methods have been explored to determine outdoor concentrating photovoltaic (CPV) cell temperature, no method has proven to work across all module technologies and result in desirable uncertainties. Menard (2012) has recently published results claiming accurate measurements of cell temperature using the wavelength shift of light emitted from the sub-cells of a Semprius CPV module. This work focuses on efforts to verify Menard's results using additional CPV technologies that are on-sun at NREL. Baseline electro-luminescence emission is recorded for modules under a low level forward bias and under isothermal conditions using thermal chambers. The same modules or sister modules are then placed on NREL's high accuracy two-axis tracker for outdoor measurements. Photo-luminescence emission peaks are measured for multiple modules at stable wind and irradiance conditions. Emission results from the sub-cells are compared to what is documented in the literature for the given semiconductor material. The signal to background ratio is analyzed and the possible broad applicability of this procedure is discussed.