Atmospheric transmittance model for a solar beam propagating between a heliostat and a receiver

Formulae are presented that provide estimates of the transmittance for a solar beam propagating between a heliostat and a central receiver. These formulae are wavelength independent, functional fits to the tabulated data of Vittitoe and Biggs, which in turn are from numerical integrations of spectral transmittance data calculated with the aid of the computer code LOWTRAN 3. The formulae allow for interpolation and extrapolation, and they have a form characteristic of atmospheric transmission models. The transmittance model contains five explicit physical variables (the site elevation H, the atmospheric water vapor density rho, the scattering coefficient ..beta.., the tower height h, and the slant range R) and three implicit variables (the season of the year, the climatic region, and the site elevation H) because rho and ..beta.. are dependent on these three variables.