Comparison of three models to estimate the slant path atmospheric attenuation in central receiver solar thermal plants under Indian climatic conditions

Abstract

This paper compares three attenuation models for the distinct meteorological conditions of India and assesses the feasibility of using the satellite data to calculate the slant path extinction coefficient and the slant path transmissivity of the lower atmosphere. The attenuation models are compared for the sites of Pune, Kanpur, and Jaipur. The AERONET data is used with REST2 to model the direct normal irradiance and the total optical depth. The results indicate that the three models give similar transmissivity values for low aerosol concentrations. As the aerosol concentrations increase, the difference in the slant path transmissivity as calculated by two of the models increases with respect to the third reference model. The slant path transmissivity comparison shows that for AERONET AOD at 550 nm (AOD550) less than 0.3, the relative error in the transmissivity values estimated by two of the compared models with respect to the third model is not higher than 10 % for Pune, 18 % for Kanpur, and 12 % for Jaipur. The mean relative error in the slant path transmissivity values obtained from the reference model using MODIS data with respect to the values obtained using AERONET data is 4.8 %, 10.2 %, and 9.2 % for Pune, Kanpur, and Jaipur, respectively. A difference of 0.2 between AERONET AOD550 and MODIS AOD550 values resulted in a difference of 0.05–0.08 between the transmissivity values calculated by the reference model using AERONET AOD550 and using MODIS AOD550 for the three sites.