Introduction: Parabolic Solar Oven

This is an instructable to show how to make a parabolic solar oven out of plywood.

It's perfect for my utilisation : it makes one liter of water boil in 15-20 minutes and cooks a meal for 3 people in something like 45-60 minutes on good days

The parabola is approximately 1.5 m wide and 50 cm deep. The larger the aperture size, the more powerful it becomes. It's quite stiff as it is with the bamboo ring, but if you want to make it bigger, you'll need to find some other ways to stiffen it.

Step 1: The Petals

The idea is that if the parabola is cut symmetrically along 8 radial directions and flattened out, then it would appear like an 16-petalled flower. So once you have the petals made of any flexible material you can bend them in the shape of a parabola.

I used 5 mm thick plywood. I think you can use a thinner plywood, but then you'll need to add a stronger structure to stiffen the parabola. Have a look here, they use a metallic structure to keep everything stiff.

I used this publication to calculate the dimensions of the petals. I had to tweak it a little bit to have something i could actually use.

Here is a google spreadsheet with everything you need (you can download it to modify it). I've also included an .ods file called parabola calculator.ods. You can :

  • modify the focal length of the parabola

  • modify the number of petals

  • choose the length of the petals

I've also included a petal in svg that I created using Inkscape. You can laser-cut the petals if you have access to a fablab !

Once you've cut the petals, drill holes every 20 cm along the sides of the petals so that you attach them together with the plastic cable ties.

Step 2: The Discs

The discs will force the bottom of the parabola to be plane. Without them, it's just impossible to bend the plywood !

Cut two discs of 20 cm out of plywood. Divide them like a pie in 16 equal parts and drill holes 2 cm from the outside of the discs.

Drill a hole of the same width 8 cm from the base of each the petal.

Sandwich the petals between the two discs using bolts.

Step 3: Bending the Plywood

I've used plastic cable tie to hold the plywood together. I've found it easier to go gradually from the center to the edges of the parabola as shown in the pictures. You can also circle the parabola with a rope, it will help.

Step 4: Adding the Aluminium

The aluminium will reflect the sunlight on the cooking pot. I used 2 adhesive aluminium tapes of 25mx5cm which cost me 10 € each.

I've found that is better to add the aluminium tape when the plywood is already bended (else the surface won't be flat once bended)

Step 5: Welding the Pot Holder

The pot holder is on the focal axis of the parabola so that it can also be used as a pivot for the parabola.

The position of the pot holder depends on the shape and the size of your parabola but in any case you can find it in the spreadsheets of the first step.

Drill a hole on two opposite petals. I used an electric wood saw to cut an ellipse (the intersection of a parabola and a cylinder can be approximated by an ellipse). The cylinder I used has a diameter of 4cm so I cut an ellipse of 4x6cm.

The welding should be very strong! I've added two extra "branches" on each side because of the weigth of the pot (I have a pot of 20L).

The place where you put the pot should be a bit lower than the rest so that the center of the pot will be on the focal point.

Step 6: The Bamboo Ring

I used a big green bamboo pole that I cut in 4 to stiffen the parabola.
The parabola could be stiffer, but it's alright like this !

Bamboo poles are very easy to cut, use a big knife and a hammer. Cut it while green and flexible and then let it dry on the parabola.

Step 7: The Support and Extras

The support should be strong enough for the parabola and the cooking pot. I made it stiffer by adding wood along the diagonal.

I've also added a little handle to the parabola so that it is easier to rotate and to transport.

That's all! If there's any problem, feel free to comment or to contact me. Have fun!

Comments

author
DavideB28 (author)2016-09-21

Hi!

Many thanks for your great instructions!

I would like to replicate the model, but step 3, that is bending the plywood, seems to me quite a demanding task, because it is not clear to me how to bend the plywood in the right shape. Did you use any mold or the like?

Thanks in advance for the reply!

Davide

author
yasintoda (author)DavideB282016-11-09

Hi davide,

I didn't use any mold, the shape of the petals was enough to make the parabola. I tightened the cable ties going from the center to the exterior of the parabola, one row at time. The parabola will gradually take its shape. I also used ropes on the exterior side of the petals . Each rope connected two opposite petal and was tightened slowly to help the positionning of the cable ties. It did help for the bending.

author
DavideB28 (author)yasintoda2016-11-10

Hi Yasintoda,

many thanks for your clarifications. It's a good information to know that there is no need for a mold and that the parabola will gradually take its shape thanks to the cable ties and the supporting ropes. Your example is really a good and economic solution for a parabolic oven, thanks again for having shared it, I hope to be able to replicate the model in a similar way!

Bests
Davide

author
Ravundra Pardeshi made it! (author)2016-06-13

I made it with cardboard. Was able to boil half a liter of water in 20 minutes. Easy to make. I am improving on Stand.

IMG_20160613_184315.jpg
author

Awesome Ravundra !!

author
vaniastolze (author)2016-10-25

Your parabol solar cooker is amazing!!! Congratulations for the project, and many thanks for sharing!!!!! :)

author
TheAZAndyman (author)2016-10-09

I wonder if poster board and mylar emergency blanket would work. It would be lighter maybe easier to work with (bend) It would need a rigid frame but I am thinking 3 different size rings of wood or something like irrigation tube. I do like the frame for holding not only the parabola but the cooking pot as well. It allows it to be rotated to safe position for storing.

author
ChunxiaH (author)2016-08-09

Ask how to calculate a petal, please explain in detail

author
liyawei (author)2016-06-04

Awesome design

author
croxly (author)2016-02-05

My ply wood wont bend without snapping. It is 5mm plywood exactly like you used. How can I fix this problem without spending crazy amounts of money?

author
PcharlyG (author)croxly2016-04-12

drop little quantity of water in the plywood. It Could help you to bend your plywood sheets.

author
swapnilkhalkar (author)2016-02-03

Can 1.25m dia. parabolic collector work??

author
bell an (author)2014-07-09

excellent work ,i was going to do the same thing,

how much the reflective duct tape cost you ?

author
yasintoda (author)bell an2014-07-11

thanks! it was 20€ for the 2 adhesive aluminium tapes

author
bell an (author)yasintoda2015-07-03

thanks for answering。

author
Jasa PindahanD (author)2015-06-20

Good job, Nice idea
to recycle old satellite dishes. You still can use those dishes and watch
satellite TV. http://pengangkutan-ekspedisi-di-medan.blogspot.com/
You should try it to recharge or create a power source. Use aluminium offset
printing plates. You can get them from offset printing companies. Using them
will be lighter, quicker, cheaper, water proof, more precise and pretty much
just as reflective.

author
Kml_s Lab (author)2015-04-02

where is youtube??

author
GavinV1 (author)Kml_s Lab2015-04-23

youtube.com

author
ykohavi (author)2015-03-16

yasintoda - I made a python script (based on your spreadsheet) to auto generate the svg templates (petals.svg, discs.svg) according to different parameters. I can send it to you if you like (let me know who)..

Thanks for the great instructable!

author
kwacka (author)2014-11-07

Following my comment that oven bags might not be suitable, Lonejack wrote: "Not true, The oven bags are made to withstand a standard over up to 450 degrees."

I would like to point out that parabolic reflectors solar ovens can reach temperatures at their focal point of 290°C (554°F).

author
lonejack (author)2014-11-07

Here is an upscale solar cooker on the market.

file:///C:/Users/PAUL/Documents/Solar%20cookers%20and%20water%20purifiers/One_Earth_Designs_Press_Kit.pdf

https://www.oneearthdesigns.com/shop/

The cost is $499 USD, 2014
If You are serious about solar cooking, this is a good buy, if You consider that this unit would last several years if maintained correctly.

author
SolarFlower_org (author)2014-07-11

Nice.

A clear oven bag around the pot will decrease your cooking time a lot, tho you'll have to vent the steam somehow or it'll fog.

Maybe look at using aluminium offset printing plates instead of the plywood and alu tape. You can get them super cheap from offset printing companies (they can only use them once) and using them will be lighter, quicker, cheaper, water proof, more precise and pretty much just as reflective. To cut them you can score them metal with an exacto, give it a couple of flexes, and tear out the line.

Main consideration with them is that they're highly anisotropic, which means they reflect tightly in one direction but completely blown out in the other, so you'll need to make sure to curve them across the grain. Contact me if you have any questions about this, I've worked with them a bit (currently making a pure alu parabolic trough) so can fill you in on the details.

author
kwacka (author)SolarFlower_org2014-07-18

A clear oven bag is useful in panel-type box ovens but are likely to melt when using a parabolic.

author
lonejack (author)kwacka2014-11-07

Not true, The oven bags are made to withstand a standard over up to 450 degrees.

author
SolarFlower_org (author)kwacka2014-07-19

A proper oven bag should be able to take 200 C, what temp does the cooker get up to?

author

Also, best not use thermal blankets for this kind of thing, they're
usually not nearly as reflective as they seem. Proper hydroponic mylar
is much better, tho a little hard to find, and like any mylar does not hold up remotely well against any kind of outside environment. It'll degrade in weeks. Which is a shame, as it's ridiculously reflective.

As a complete aside, be aware that this device will also make a very effective reflector for wifi/mobile.

author

thanks a lot for the idea of aluminium offset printing plates! I will try to find an offset printing company and i'll contact you then if I have any trouble. I just hope that the aluminium sheets will be large enough!

author

The ones I'm working with now are 100x80cm, which is pretty huge. Generally they're in the 70x60ish kind of range. Shouldn't be more than about a dollar each.

In terms of understanding how the grain works for the anisotropy, bounce a laser pointer off a plate, you'll see what I mean.

author
SparkySolar (author)2014-10-19

I like your Instructable

Thank you so much for sharing

Rima

author
domenic3 (author)2014-09-02

very smart idea that uses the suns energy!!

author
Mark Rehorst (author)2014-07-10

Very elaborate! I'd recommend using black cable ties instead of the white ones- the black ones are UV resistant and will last longer in ANY outdoor application.

You can make a light weight parabolic reflector with variable focal point by pulling a partial vacuum behind a sheet of metalized polyester film stretched on a circular frame. "Rescue blanket" film works well. I made a small one (12" diameter) a few years ago and it set fire to leaves placed at the focal point in about 5 seconds.

author
Verga (author)Mark Rehorst2014-07-10

Where do you get the metalized polyester film? I have an idea for a similar project using Satellite dishes, and the cost of 3/4 inch square mirrors is prohibitive. As is the thought of gluing down that many small mirrors and aiming them at the same focal point.

author
Mr_Liss (author)Verga2014-07-15

I got lots of cheap emergency blankets (1/2 dozen) from Sierra Trading Post.

author
rodenbach (author)Verga2014-07-14

Try

http://www.solarcooker-at-cantinawest.com/vinyl_reflective_material_self_adhesive.html

author
anorton7 (author)Verga2014-07-11

Have you thought about using the shiny side of aluminum foil? I'm not sure if it's quite as reflective as a mirror, but it's certainly cheaper.

author
agulesin (author)Verga2014-07-10

A few years ago we made a satellite-dish based solar "oven" by sanding down the original painted surface (it had small dimples all over) and then sticking normal cooking foil (Aluminium) all over the surface (bright side out).

It worked well and we managed to boil an egg (and eat it!) in about 20 mins of good sunlight. A small saucapan was hung in the location which would normally be the LNB (device that takes the satellite signal to the TV). The dish was about 90cm diameter but of course a bigger one would be more efficient.

With the metal film you'd have to maintain the vacuum while it was working which seems to be against the efficiency of such a gadget (why not use the electricity which you'll use to run the vacuum pump to cook things in the first place!)

author
Mark Rehorst (author)agulesin2014-07-11

No pump is needed. The film is lightly stretched and glued (contact cement sticks to polyester film and almost anything else) over a circular opening in a frame with a closed back. This forms an air-tight drum of whatever size you decide to use. You can draw the necessary vacuum by simply sucking on a valve mounted on the frame of the reflector, then close the valve (that's how I did it with the small one I made). The more you suck, the shorter the focal length of the mirror.

author
Mark Rehorst (author)Verga2014-07-10

Here's an example: http://goo.gl/GSpDIj

author
Verga (author)Mark Rehorst2014-07-10

Thank you

author
redrok (author)Verga2014-07-10

Hi Verga;

The vacuum causes the film to produce a section of a sphere, not a paraboloid.

Ok, close enough for many small applications with long focal lengths, but not a deep dish like yasintoda is describing.

redrok

author
Verga (author)redrok2014-07-10

I understood that I was just looking for the reflective material, but thank you

author
wizodd0 (author)Verga2014-07-10

Window film to protect from sun. you can buy in anything from full reflective to full transmittance. Google 'reflective window film'

author
Verga (author)wizodd02014-07-10

Thanks

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yasintoda (author)Mark Rehorst2014-07-12

thanks for the information about the black ties, I'll give them a try next time!

author
Eh Lie Us! (author)2014-07-15

Excellent!

author
omikeo (author)2014-07-10

nice job, how hot does it get ? do you need direct sun and a cloudless day ? what have you cooked with it ? Thanks, mike

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yasintoda (author)omikeo2014-07-11

thanks mike! I don't really know how hot it gets, but you can cook even when it's a little bit cloudy. I have a cooking pot with some inertia so it makes up for the clouds on these days. Until now I've cooked large vegetarians meals and infused tea with it but I think you could cook nearly everything (it just takes more time)

author
omikeo (author)yasintoda2014-07-12

a large one could run some kinda steam generator, would you think, isn't that how those mirrors arrays work, i guess living at a proper latitude(no snow more sun etc) and having it self track the sun, would make a difference ? I wonder what's more efficient that technique or photo voltaics ?

author
Kiteman (author)2014-07-09

Nice job.

Where in the world (roughly) are you using it?

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yasintoda (author)Kiteman2014-07-11

thanks kiteman! I live close to the french alps