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 total energy, can impact 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 1970s 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.

Solar Resource for Space and Terrestrial Applications

“…This dataset has been quality controlled and is now available online. 10 More recently, similar data have been obtained with different experimental setups installed at solar furnaces in Switzerland [53] and Germany [54] . Recent studies show to what extent these different results were in agreement, while providing simplifi ed analytical modeling that might be used in concentrating systems (e.g., see Reference 55 ).…”

Concentrator Optics for Photovoltaic Systems

“…In contrast to the detailed physical simulation of the concentrator Fresnel lens, the efficiency of the solar cell was calculated with the program etaOpt [41] which determines the theoretical maximum solar cell efficiency given by the Shockley-Queisser limit [42]. The ASTM G173 direct normal plus circumsolar irradiation spectrum [43] and mean angular irradiation profiles [44] with the additional assumption of 0.1 ∘ tracking tolerance were used to calculate the overall system efficiency for each point on the distance-temperature-map. More details on the simulated system can be found in Refs.…”

High‐Concentration Fresnel Lens Assemblies and Systems

“…The direct irradiation incoming within an opening angle between ± 0.3 ° and ± 2.5 ° is called circumsolar irradiation, and the intensity is typically 5 -20% (= circumsolar ratio, or CSR) of the direct sunlight [21] , depending on the atmospheric conditions. As can be seen from Figure 14.5 A, the CSR is poorly utilized by the Fresnel lens.…”