Calculation of a solar parabola: focus, curvature ...

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Calculation of a solar parabola: focus, curvature ...




by Christophe » 20/05/10, 11:48

It is finally beautiful, I restart my experiences of solar concentration (started here https://www.econologie.com/forums/produit-de ... t9584.html )

This subject is intended to calculate and size a solar parabola but also, probably more affordable and effective, a linear parabola (parabolinic concentrator).

The question is simple: find the focus in relation to the curvature and find the best curvature!

Example, I have a piece of flexible synthetic mirror of 0.5 * 1m, if I "curve" it in the direction of the width on X cm (X <50 cm) where will be placed the hearth?

Answer here: http://canarlake.org/index.cgi?theme=fo ... hsparabole

The subject has already been mentioned in other subjects, I copy / paste some info to have the basics:

https://www.econologie.com/forums/paraboles- ... t5996.html

Christophe wrote:For those, like me, who want to start building a parable, here is a summary message, from the forum of Edgar Nazar solar towers

Christophe wrote:Ok Remundo, Obelix superb link makes you want to build!

Image
Image
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He could put a little stirling without problem!

So I recap:
http://f5dm.club.fr/geodesic/index.html (dead link too bad)
+ http://canarlake.org/index.cgi?theme=fo ... geodesique
= everything to do his parable even!


A little trick found on the 2ieme link (would not be Auvergnat the author : Mrgreen: :

But it still costs all these cleats!

You noticed, too? A cleat is not expensive. But if you want a mesh of 8 x 8, so 2 times 9 cleats, it is immediately think ...

So thinking, you think you have better buy a plywood plate, and cut thin strips parallel in, as a cleat. I think you're right!


Read also: https://www.econologie.com/forums/schema-ele ... t8495.html
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by Christophe » 20/05/10, 12:13

Another complete site with theoretical calculations:
http://pagesperso-orange.fr/f4buc/calcul_geodesique.htm
http://pagesperso-orange.fr/f4buc/parab ... sique2.htm

Even if the application on this site is the radio, it is exactly the same thing as a parable at the dimensional levels, there is just the reflector that changes ...
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by elephant » 20/05/10, 13:34

in radio, there is the additional problem of frequency.
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by chatelot16 » 23/05/10, 21:43

Frequency does not do anything for the shape of the parable!

the frequency counts only for the type of reflector

5cm mesh is a good reflector for the terrestrial television frequency: satelite television passes through

for the microwaves of the perforated plate 1mm is still reflective

for the satelite tv it takes the full plate but not necessarily polite

for the light it takes polished metal like a mirror
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by gegyx » 23/05/10, 22:37

Uh! Near the equator, the large satellite dishes capturing the geostationary satellites at the zenith, let the monsoon pass ...

: Lol:

I would like to present you a picture taken last April (summer) in Thailand.

Image

You have the orientations, the structure, the mesh, the foot ...
the gardener
and all my contribution.

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by chatelot16 » 23/05/10, 22:44

if a cylindrical parabole concentrates x4 the same in true paraboloid will concentrate in 4 x 4 = 16: it is still better

remains to know what is the purpose, and what means of construction

to make a paraboloid of revolution a good method is the polyester and fiberglass: remains to make the mold

a solution: stone and cement masonry, plaster finish with a wooden gabari cut in parabola
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by gegyx » 23/05/10, 23:39

The solar oven

Image

It is quickly mountable but rather light ...

taken at Jonzac in 2007
https://www.econologie.com/forums/jonzac-vil ... t3975.html
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by Christophe » 24/05/10, 12:15

I managed to find a document that more or less replaces the dead link above: https://www.econologie.com/telechargeme ... satellite/
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by chatelot16 » 24/05/10, 13:24

the first question is how to find the focus of a curve? is this the good question

I prefer to draw the curve that puts the focus or I want

for the maths there is the equation, but there is also the geometry: if I want a focus at 50cm in front of the bottom of the parabola I draw a line 50cm behind the parabola: to look at the compass the point equals distance between the right and the focus: it draws a beautiful parable


more practically trace the perpendicular line to the axis passing through the bottom of the parabola, draw a parallel line 1 cm forward: draw a circle around the focus of 51cm: the intersections give 2 point

another right 1 cm more forward another circle 1 cm larger .....

it draws a parable that can serve as a gabari to make a paraboloid of revolution


the geodesic metheode to build the parable does not please me much: it requires a great precision of drilling lates for a correct result

as long as I have precise mechanical parts, I would prefer to cut pieces in sheet well drilled on the edge so that these pieces screwed together make a beautiful paraboloid
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by dedeleco » 24/05/10, 13:53

Well-known factual reminder:
parabola = ellipse with a focus at infinity, and so we draw a parabola with a pencil or stylet sliding on a string (or wire) stretched, almost too short, attached to two points (or nails) far apart (30m) which gives a very flattened ellipse, which is a parable in the vicinity of each nail !!

By moving the nail on the axis of the parabola (small liteau and string stretched), we try to follow the parable, the best possible and we get the focus! (the other nail, or focus, with almost infinite is on the axis of the parabola, very far).

In my opinion, the least tiring, with also facing the sun in the axis to find the point that heats the most (strong thermocouple, behind black metal, not calibrated, as brazing son copper-iron and millivolmeter, amp 741 or LM356 of factor 1000 and voltmeter) or the brightest, well white.
This last method makes it possible to measure the imperfections !!
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