Principle of operation and basic parameters of the solar parabolic cooker
The reflector of a solar parabolic cooker (SPC) is axially symmetrical and shaped so its cross-section is a parabola; for that reason it has the property of bringing parallel rays of sunlight to a focus. What we have in parabolics is actually a focus spot with small but finite dimensions rather than an infinitly small focus point. If the axis of symmetry is aimed at the sun, a metal object that is located at the focus spot receives highly concentrated sunlight, absorbs it and therefore becomes very hot. This is the basis for the use of this kind of reflector for solar cooking.
Relevant to the functioning of SPC is only direct solar radiation(DSR), being measured in W/m2. That's radiation reaching SPC as a beam of parallel rays directly from the sun.
Relationship between the basic SPC parameters
The diameter D and the depth t of the reflector are subject to direct measurement. Other parameters are calculated as a function of D and t:
1 / focal length f = (D/2)^2/(4t)
2 / aperture A = п.(D/2)^2
3 / reflector area S = (2п/3p).(b^3 - p^3), where: p = 2f, b = sqrt(2.p.t + p^2)
4 / average solar cooker power Pm = 700 x A, calculated for DSR = 700 W/m2
5 / maximum solar cooker power Pmax = 1000 x A, calculated for DSR=1000 W/m2
Basic SPC parameters illustrated by the cookers of HoSa Solar Ltd.
Model LD150 LD180 SK-01
- D = 150 cm 180 cm 140 сm
- t = 24 cm 29 cm 47 сm
- f = 58.6 cm 69.8 cm 26 сm
- A = 1.77 m2 2.54 m2 1.54 m2
- S = 1.94 m2 2.75 m2 2.09 m2
- Pm =1200 W 1800 W 1100 W
- Pmax = 1800 W 2500 W 1500 W
AB - diameter of the reflector
OT - depth of the reflector
OF - focal length