Abstract :
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
