Representative Terrestrial Solar Brightness Profiles

Abstract

Solar thermal energy systems often use optical imaging concentrators. The image size and shape produced in the focal plane of the concentrator system depends on the solar brightness distribution. Therefore, the forward scattering of solar radiation by the Earth’s atmosphere modifies the solar brightness distribution and creates a circumsolar aureole. The circumsolar ratio, the energy contained in the solar aureole compared to the total solar energy, can have an impact on the performance of these concentrating systems. Based on about 2300 sunshape measurements from sites in France, Germany and Spain made with a camera system developed by the German Aerospace Center (DLR), average solar brightness profiles with a circumsolar ratio of about 0%, 5%, 10%, 20%, 30%, and 40% were generated. These profiles are compared to the measurements taken by the Lawrence Berkeley Laboratory (LBL) in the late 1970’s and a commonly used limb-darkened solar brightness profile, as known from astronomy. A statistical analysis gives information on the frequency of occurrence of each of the average profiles. The profiles combined with the statistical weight should offer a numerical database for calculating the influence of variable conditions of the sunlight scattering on solar concentrating systems. Furthermore, a single average profile was calculated from the DLR data.

Best Practices Handbook for the Collection and Use of Solar Resource Data for Solar Energy Applications

“…Rabl and Bendt (1982) and Neumann et al (2002) This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.…”

“…Here it refers to an average of many sunshapes that deviate strongly from the so-called "standard solar scan." "DLR mean" shows an average sunshape derived from DLR's measurements as presented under this name in (Neumann et al 2002). The other sunshapes are averages of sunshapes within different intervals of CSRs (circumsolar ratio) from (Neumann et al 2002).…”

“…"DLR mean" shows an average sunshape derived from DLR's measurements as presented under this name in (Neumann et al 2002). The other sunshapes are averages of sunshapes within different intervals of CSRs (circumsolar ratio) from (Neumann et al 2002). They are named corresponding to the CSR interval that was used for the averaging.…”

Quality control of Fresnel lens molds using deflectometry

“…The latter corresponds to a geometrical concentration ratio of C geo~ 385x what might be relatively low compared to other high concentrating CPV systems [8]. Finally, a monochromatic ray tracing with a circumsolar ratio of 5% (sun shape distribution CSR5 defined in [9]) is conducted in order to simulate the irradiation beneath a Fresnel lens model including the measured surface normals. The aperture of Mold A is cropped to the error prone part in the center with quadratic dimension 4 mm x 4 mm.…”

IEA SHC Task 49/IV - Deliverable A3.1 - Guideline on testing procedures for collectors used in solar process heat

“…For different CSR, different sunshape descriptions are available (Neumann et al 2002). The relative intensity over the solar disc and circumsolar region is plotted for three circumsolar ratios in Figure 4.…”