Cutting and drilling plans for flat metal segments to make an approximate parabolic reflector suitable for a solar concentrator or solar cooker
Legend x : perpendicular dist. of point from axis (radius) y : distance of point from centre of dish along axis arc : distance of hole from centre, measured along surface of parabola arc' : distance of holes from centre, measured along centre of segment hole c/c : req. distance between hole centres when drilled at given radius Eff. area : Effective captive area perpendicular to axis Pmax : Maximum solar power collected by dish (assuming =1000?>W/m² and =90?> % reflection )
(dx)² : square of incremental change in x
(dy)² : square of incremental change in y
dS : incremental change along strip
parabola : y=x²/300 focal length =75
calculation radial increment= 2 ; results (diam.) shown every 10
Eff. area /m²
Eff. area /m²
segments per sheet=8;
Number of sheets (250 cm x 125 cm) required for 21 segments = 3
Warning: focal point falls 15 cm in front of reflector dish.
Possible suppliers of reflective Al sheet:
Alcan "Eloxal" - manufacturer (worldwide corp. find your local distributor) Alanod Mirosolar. German company, UK/US Offices (avoid stainless steel which absorbs IR and gets hot.)
Care should always be taken when designing and using solar concentrators to avoid the possibity of burns. Please note that concentrated infrared heat is invisible but can burn like red hot metal. The focal length should be kept short to avoid someone in front of the parabola passing through the concentrated beam.
Principal of calculation
The above tables are calculated by numerical integration of the arc of the parabolic section as follows:
Determine the quadratic equation of parabola from diameter and focal length.
Use incremental changes in x and y and pythagorus to calculate incremental lengths along parabola arc.
Sum to obtain successive drilling points, use cosine of semi-angle to project distances onto segment centre line
Use sine of semi-angle to find distance between hole pairs as a chord of each circlular cut through paraboliod.
Add selected clearance for drilling and plot sheet metal plan.
The power is the product of the effective area taken perpendicular to the axis of the paraboloid, the insolation and the reflectivity of the sheet.
NB. Drilling Accuracy in the distance between hole pairs is essencial to getting the desired profile. Inaccuracies will defocus the beam to a larger volume around the focal point.
The information on this page is provided AS IS. The author and domain owners make no waranty, expressed or implied of it's suitability for a given purpose.
This page is generated by a PHP script as a function of the data entered, not by fully engineered software. It has not been thoroughly
tested under extreme conditions and results should not be used in critical applications, including but not limited to
: life-support systems, nuclear power stations, aerospace applications, guided missile systems, penile temultulance detectors, etc.
If you are designing a parabolic solar reflector the results should be reliable enough.
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parabolic solar reflector calculator v0.25 . 25 Nov 2008