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Research Papers

View Factors of Flat Solar Collectors Array in Flat, Inclined, and Step-Like Solar Fields

[+] Author and Article Information
Nassar Yasser Fathi

Professor
Mechanical Engineering Department,
Engineering and Technology Faculty,
Sebha University,
Brack 721, Libya
e-mail: yasser_nassar68@ymail.com

Alsadi Samer

Associate Professor
Electrical Engineering Department,
Faculty of Engineering and Technology,
Palestine Technical University—Kadoorie,
Tulkarm 31, Palestine
e-mail: samer_sadi@yahoo.com

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.

J. Sol. Energy Eng 138(6), 061005 (Sep 15, 2016) (8 pages) Paper No: SOL-16-1186; doi: 10.1115/1.4034549 History: Received April 23, 2016; Revised August 26, 2016

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.

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Copyright © 2016 by ASME
Topics: Solar energy
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References

Figures

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Fig. 1

Deployment of collectors on (a) a flat solar field, (b) an inclined solar field, and (c) a step-like solar field

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Fig. 2

Calculation of view factor by means of crossed-strings method for two surfaces of infinite length on a flat solar field; (a) sky-view factor FL2−sky, (b) ground-view factor FL2−ground, and (c) rear-side view factor FL2−l1

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Fig. 3

Calculation of view factors by means of crossed-strings method for two surfaces of infinite length mounted on an inclined field; (a) sky-view factor FL2−sky, (b) ground-view factor FL2−ground, and (c) rear-side view factor FL2−l1

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Fig. 4

Representation of the step-like solar field in terms of the inclined solar field

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Fig. 5

View factors for a flat-solar field; (a) sky-view factor, (b) ground-view factor, and (c) collector's rear-side view factor

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Fig. 6

View factors for an inclined solar field; (a) sky-view factor, (b) ground-view factor, and (c) collector's rear-side view factor

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Fig. 7

View factors for a step-like solar field S1 = S2 = 30 deg; (a) sky-view factor, (b) ground-view factor, and (c) collector's rear-side view factor

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Fig. 8

Demonstration of calculation of x at the solar noon in (a) a flat solar field, (b) an inclined solar field, and (c) a step-like solar field

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Fig. 9

Maximum collector's dimensionless height for deployment of collectors on (a) flat solar field with various latitudes, (b) inclined solar field for latitude 30 °N with various inclination field ε, and (c) step-like solar field for latitude 30 °N with various step dimensionless y/xs

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Fig. 10

State of problem for ground-reflect radiation, presenting the shadow zone and sunny zone, where Z1 is the shadow zone, Z2 is the effective sunny zone, and Z3 is the actual sunny zone in the step-like field

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Fig. 11

The dimensionless sunny zone length for the 21st of every month for various collector's dimensionless height (L1/xf) at latitudes (λ) of (a) 0 °N, (b) 30 °N, and (c) 40 °N and the collector tilt angle S1=λ

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Fig. 12

The dimensionless sunny zone length for the 21st of every month for various collector's dimensionless height (L1/xi) and land inclination angles ε for latitude S1=λ=30 deg

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Fig. 13

The dimensionless sunny zone length for the 21st of every month for various collector's dimensionless height (L1/xs) and step dimensionless height y/xs for latitude S1=λ=30 deg

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