The Spectral Directional Emissivity of Photovoltaic Surfaces

Photovoltaic solar cells are used for the direct conversion of solar radiation to electric power.To evaluate the efficiency of this energy conversion process, all in- and outgoing fluxes in the thermodynamic balance equations for energy and entropy must be known.The spatial and spectral distribution of radiation energy iIntensities must be known to calculate the radiation energy fluxes.To calculate the entropy fluxes, additional information on the coherence properties of the radiation field is essential.This information is expressed by the degree of polarization.First results of measurements of the optical properties of a solar cell are preseInted.The calculation procedure to obtain the outgoing energy and entropy fluxes is described.The experimental apparatus introduced in this paper yields the spectral directional emissivity by comparing the sample radiation with the radiation from an isothermal cavity.The degree of polarization of the emitted radiation is determined by a retarder/polarizer set within the apparatus. Both quantities are measured in the infrared region for wavelengths between 4.0 and 20.0 mm.