An Evaluation of Satellite Estimates of Solar Surface Irradiance Using Ground Observations in San Antonio, Texas, USA

Shuang Xia,Rolando Vega,Hongjie Xie,Alberto Mestas-Nuñez

doi:10.3390/rs9121268

Abstract

Estimates of solar irradiance at the earth’s surface from satellite observations are useful for planning both the deployment of distributed photovoltaic systems and their integration into electricity grids. In order to use surface solar irradiance from satellites for these purposes, validation of its accuracy against ground observations is needed. In this study, satellite estimates of surface solar irradiance from Geostationary Operational Environmental Satellite (GOES) are compared with ground observations at two sites, namely the main campus of the University of Texas at San Antonio (UTSA) and the Alamo Solar Farm of San Antonio (ASF). The comparisons are done mostly on an hourly timescale, under different cloud conditions classified by cloud types and cloud layers, and at different solar zenith angle intervals. It is found that satellite estimates and ground observations of surface solar irradiance are significantly correlated (p < 0.05) under all sky conditions (r: 0.80 and 0.87 on an hourly timescale and 0.94 and 0.91 on a daily timescale, respectively for the UTSA and ASF sites); on the hourly timescale, the correlations are 0.77 and 0.86 under clear-sky conditions, and 0.74 and 0.84 under cloudy conditions, respectively for the UTSA and ASF sites, and mostly >0.60 under different cloud types and layers for both sites. The correlations under cloudy-sky conditions are mostly stronger than those under clear-sky conditions at different solar zenith angles. The correlation coefficients are mostly the smallest with solar zenith angle in the range of 75–90° under all sky, clear-sky and cloudy-sky conditions. At the ASF site, the overall bias of GOES surface solar irradiance is small (+1.77 Wm−2) under all sky while relatively larger under clear-sky (−22.29 Wm−2) and cloudy-sky (+40.31 Wm−2) conditions. The overall good agreement of the satellite estimates with the ground observations underscores the usefulness of the GOES surface solar irradiance estimates for solar energy studies in the San Antonio area.

Highlights

Solar irradiance is the solar power per unit area (Wm−2) received from the Sun in the form of shortwave electromagnetic radiation
Otkin et al [16] found that the correlation coefficient for the seasonal comparison of Gs retrieved from a physical model and Gg on different timescales at 11 sites was high (0.95), with a bias of 8 Wm−2 (GOES_E) and −9 Wm−2 (GOES_W) and root mean square error (RMSE) of 63 Wm−2 on an hourly timescale, and the bias of 4 Wm−2 (GOES_E) and −17 Wm−2 (GOES_W) and RMSE of 16 Wm−2 on the daily timescale
This paper examines the correlations between Gs and Gg on different timescales, under different sky conditions, different cloud categories and solar zenith angles

Summary

Introduction

Solar irradiance is the solar power per unit area (Wm−2) received from the Sun in the form of shortwave electromagnetic radiation Because it is an abundant source of green energy, solar irradiance has a great potential for various types of applications in the near future including water treatment plants [1,2], water supply and sanitation [3,4], environmental protection [5,6,7], and as an alternative to fossil fuel energy generation [8,9]. Since January 1996, the National Oceanic and Atmospheric Administration (NOAA)/National Environmental Satellite, Data, and Information Service (NESDIS) has retrieved parameters for evaluating the surface shortwave radiation balance from the Geostationary Operational Environmental Satellite system (GOES) in real time [10,11] These satellite observations have allowed the implementation of radiative transfer models for solar radiation. The observational data of G comes from satellite estimates (Gs) and ground direct measurements (Gg)

Satellite Estimates

Ground Observations

Findings

Conclusions