S unshape distributions for terrestrial solar simulations

In considering solar concentrating systems, the energy distribution in the focal plane depends, among other things, on the radial distribution (sunshape) of the incident solar energy. Individual sunshapes are created by the small angle forward scattering of sunlight off aerosols in the troposphere, having the effect of transferring some part of the solar energy from within the solar disk to the circumsolar aureole. The ratio of the amount of energy contained in the circumsolar aureole to the total amount of direct energy arriving from the sun, being that from the solar aureole and within the solar disk, is termed the circumsolar ratio (CSR) and is a useful parameter for characterising individual sunshapes. The degree to which the energy distribution in the focal plane of an optical system depends on a characteristic sunshape is usually not well defined, but it is clear that it is non-negligible. Using the Lawrence Berkeley Laboratory’s vast circumsolar database, collected from 11 sites across the United States in the late 1970s and early 1980s, and the recently published sunshapes from the German Aerospace Centre (DLR) correlating three European sites, this paper describes a sunshape model that is independent of geographic location. Further, this paper illustrates that, on average, the circumsolar ratio defines the spatial energy distribution across the solar disk and aureole, and presents an algorithm that can be used to model these distributions for simulating solar concentrating systems.  2003 Elsevier Science Ltd. All rights reserved