Solar radiation consists of direct beam, sky diffuse, and reflected radiations from the ground and adjacent surfaces. The amount of diffuse radiation falling on solar collector depends on the view factor of the collector to sky. The reflected radiation striking the collector's surface depends on the reflectivity of the surface, as well as on view factors and the amount of solar radiation reaching the reflecting surfaces. The amount of reflected radiation coming from the ground can be of an appreciable amount, and can be amplified using special reflector surfaces. This study develops general analytical expressions for the sky's view factors as well as factors related to the ground and those between collectors for the deployment of collectors in multiple rows, in three types of solar fields: flat, inclined, and steplike solar fields. All parameters presented in these expressions are measurable (edge-to-edge dimension). The effects of the design parameters such as the tilt of the angle of the collector, the distance between the collectors, the height of the collector, the position of the collector above the ground (as in the case of step-like field), and the inclination of the land of the field (as in the case of an inclined field) on the view factors are numerically demonstrated. The current study also specifies new terms such as the sunny zone and the shadow zone; these zones control the amount of solar radiation reflected onto the collector. As a result, the ground-view factor that depends on the altitude of the solar angle is considered to be a dynamic parameter. The results obtained may be used to estimate the solar radiation incident on all types of solar fields, with the possibility of increasing the incident radiation on a collector by using planar reflectors.
View Factors of Flat Solar Collectors Array in Flat, Inclined, and Step-Like Solar Fields
Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received April 23, 2016; final manuscript received August 26, 2016; published online September 15, 2016. Assoc. Editor: M. Keith Sharp.
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Fathi, N. Y., and Samer, A. (September 15, 2016). "View Factors of Flat Solar Collectors Array in Flat, Inclined, and Step-Like Solar Fields." ASME. J. Sol. Energy Eng. December 2016; 138(6): 061005. https://doi.org/10.1115/1.4034549
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