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How to make a really hot solar cooker

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Concrete Solar Concentrator

Parabola is the best shape for making solar reflector because it directs all sunlight on to its focus. The concentrated sunlight heats up anything placed at focus.

This parabolic cooker plan is quite simple. Following things are needed to make this solar parabolic cooker/heater:

  • Sand
  • Cement
  • Aluminium foil
  • Bond (that can stick foil to the cemented surface)
  • Cardboard
  • A large sheet of paper

Solar Cooker Project: What we are going to do

Our idea is to make a concrete parabolic concentrator. For that we will make a parabolic wooden template which will be swept longitudinally through a mound of wet concrete. Sweeping once or twice would give us the parabolic shape of the concentrator. We will then let it dry and then finally we would paste Aluminium foil on it.

Step 1: Draw a horizontal line on a paper

For that you should have something in mind as to what width you require for your solar concentrator. e.g. if you want to make a solar concentrator 3 feet wide, you would need a paper of more than 3 feet width. You may not get a paper of this size. In order to solve this problem you can take 3,4 large papers and stick them side by side on something flat e.g. a board. It would be even nicer if you paste these sheets directly on the wooden piece which you will use to make the template. So when you are done with sizing the paper and pasting it, draw a horizontal line arbitrarily at the bottom of the paper.

concrete-solar-concentrator

Step 2: Mark the midpoint of this line

Do this step carefully.

concrete-solar-concentrator

Step 3: Draw a vertical line passing through this point.

Carry out this step even more carefully.

concrete-solar-concentrator

Step 4: Mark the focus of the parabola

Now, this is important. You will now choose the focus. The focus is going to be the point on which all the solar radiations will converge. So mark the focus while keeping in mind the height of the pipe, pot or pan which you are going to heat using this concentrator. Here I have taken 3 feet as an example. You can take any value you wish according to your needs.

concrete-solar-concentrator

Step 5: Mark the points to make the curve.

Formula of the parabola is: x2 = 4ay

where a = focal length

Take several values of "x" with equal intervals and calculate "y".

e.g. Take x = 0.1ft and then calculate y

Then take x = 0.2ft and calculate y. With the interval of 0.1 keep taking values till the required width.

Note that both halves of the paper(as separated by the vertical line) are the mirror image of each other.

concrete-solar-concentrator

You will end up with something like this:

concrete-solar-concentrator

Step 6: Join all the points which you have marked.

Join all the points carefully. Here I am showing only a rough sketch. You should be more careful with e curve. It should be as smooth as possible. The efficiency of the concentrator depends on how accuracy of this curve.

concrete-solar-concentrator

Step 7: Saw the curve.

You had two options in the beginning. Either you could draw the curve on paper and then paste it on a wood 'plank' later OR you could paste the paper directly on thin wood board and draw the curve on it.

If you chose to make the curve first, then paste this paper on to a thin wooden board now.

Now saw out the profile and nail a piece of wood(for handle) on to this profile. This is how it should look:

concrete-solar-concentrator

Step 8: Prepare some concrete

Take two to three parts sand and one part cement and mix it well. Depending on the size of your solar concentrator, take cement and sand approximately. Add water and mix this whole stuff. Make a mound of this "sludge" as shown in the figure below. It shouldn't be as perfect as it looks in the figure below.

concrete-solar-concentrator

Step 9: Sweep the template longitudinally on the mound.

Now, sweep the template on this wet mound. Do it as many times as you wish to get near-perfect shape. Let it dry.

concrete-solar-concentrator
concrete-solar-concentrator

Step 10: Paste Aluminium foil on the structure.

Cut Aluminium foil in to pieces and paste it on the concave surface of the structure. Your concentrator is now ready for reflection.

Hang anything you like to heat e.g. pipe or pan at the focus.

Pipe or pan can be supported with proper steel, iron or wood supports at each end of the structure. Please do not touch a hot solar cooker (i.e. a concentrator that has been exposed to sunlight for a long time) as it may cause serious burns.

This concentrator works best at noon. It can be used as a hot dog solar cooker.

If you have any comments, suggestions, clarifications, queries please write them down in the comments section. I will reply you immediately.

 

Comments

Mike MacDonald on March 20, 2013:

You have never built this !

hahaha on February 12, 2013:

math are you kidding me look what time it is its so late not the good time for math.

Noel Commins on March 21, 2012:

I would like to know more about "BOB's" parabolic heater 11 mo. ago

Thanks,

Noel

net8a on March 06, 2012:

If you live in a low sun area in "step 2: mark the middle of the horizontal line", mark it off center, and draw the vertical line. Then calculate the points of the parabole with the formula (with more points on one side than the other). Finally, in step 9, sweep your template tiltled in the average direction of the sun in your community (the vertical line of step 3). You will have the concrete parabole aimed at your sun.

Best regards

Mr. Carroll D. Hampleman: (CD) on March 05, 2012:

I remember (High School) how to draw a "Parabolic Curve"

by using a pencil, a thumbtack, and a piece of string with a "loop" on one end. I made a 120 Square Foot (10 Ft. wide BY 12 Fr. High) that would BOIL water. I had Natural Gas then, so I tore it down, Now (retired in Florida) I am "RE-BUILDING" this little baby. "NO CHARGE" for details. /s/ Carroll D. Hampleman (TRACKTHESUN@YAHOO.COM)

shivaji on February 13, 2012:

i want the detils @ the magnifying lens as a solar concentrator.

Plz. anybody send me the details related to the same on shivaji1988@gmail.com

SolarWind9 from New York on November 29, 2011:

I commend your efforts. I suppose this would work well in a desert or tropics, but too far from the equator and no chance of success in cooler climates with lower sun-angle. Also, modern people like things fast and easy, this is slow and difficult. So given a choice, other than novelty, I would find this hard to sell even if it worked well. Of course, true 'off the grid' believers would make or buy one anyway and spend all day cooking their dinner. It seems like something from the preindustrial era similar to smoke-signals; seems backwards.

howard on August 04, 2011:

wouldn't just twirling the template around in the cement (or other medium) instead of dragging it through in a straight line give you a parabolic dish instead of a trough?

nokubonga on May 31, 2011:

m a chemical engineering student,n we wr assigned to design a solar desalination rig.i understand the instructions on constructing,isn't the relationship is y=x2/4f,do we assume the folal point or we also have to calculate it

bob on April 21, 2011:

I manufactured 4'x 8' parabolic 'trough' collectors out of aluminum frames with aluminized mylar reflective coatings. They focused onto an 8' length of 1" Copper Pipe with a flat black finish facing the trough. If the parabolic is precise, these are very dangerous to work around. In full sunlight, just passing your hand through the focal point causes instant burns. As a demonstration we would take a 1' foot section of the 4' wide collector and pour water into the pipe. Only steam came out the other end. If I were to make one to play with, I'd use a sheet of smooth fiberglass coated with aluminized mylar as the reflector and a frame made of plywood supports shaped to the parabola. Another interesting design I saw in the '80s was a fresnel lens as a reflector, cut into a 4'x 4'x 2" sheet of rigid insulation and surfaced with aluminum. The focal point was about an inch in diameter about 3' from the center. That's about an 1800:1 focus. ratio. Bright sun is about 1000 Watts/m^2. This collector focuses about 1200 Watts onto a square inch.

c on April 06, 2011:

our class is doing a project to make a solar oven to heat water and is their anyway to make an oven with out the concrete cause we will have to transport it from our houses to the school so please comment some ideas or comment a link....

thx

c

Shujon on March 01, 2011:

Hi,

Good evening.I am very interesting on Very hot cooker. Heat from 20 degree to 400 degree for only pressure Rice cooker. That the cook time 20 minute for rice.

please send me design and video of thus hot solar cooker.

Thanks

Shujon on March 01, 2011:

Hi,

Good evening.I am very interesting on Very hot cooker. Heat from 20 degree to 400 degree for only pressure Rice cooker. That the cook time 20 minute for rice.

please send me design and video of thus hot solar cooker.

Thanks

shrikant on February 16, 2011:

plz give the formula to calculate the radius

trulym3 on January 29, 2011:

I am trying to build parabolic solar cooker in science far

In my place , this hard buy those things which are required

So cud you please suggest me some alternative means and could you also write the methods of preparing it ?

Thank you guys for all the information .

greathub (author) from Earth on July 18, 2010:

@ Jason:

Hi Jason!

Thanks for dropping by. Probably the best way to get started is by making box solar cookers that are way less complex.

It is possible to make solar concentrators that can heat water significantly.

But its next to impossible to make a solar concentrator from household items that can drive a steam generator.

Jason Powell on July 15, 2010:

Heya Folks,

I am 27 and work in the Health field and i am interested in making a parabolic dish for my own purpose. What is the best way to get started and is this the most efficient way?

Is it possible to build one good enough to say, heat water and drive a steam generator out of normal household items etc?

I am looking forward to your replies.

Thanks

Linda Joslin from UNIVERSE on March 18, 2010:

What a brilliant idea, I love it when people start to get practical instead of just talking about it. Im going to pass the hub to those with a little more technical knowledge than myself.

Namaste

Linda at UNIVERSAL LAWS

Mr. Carroll D. Hampleman (CDH) on January 09, 2010:

I have made a 120 Sq.Ft. Parabolic that would BOIL water.

(From "Reflecting Mirrors").; The FULL SUN (approx, 1 KW/Sq.M., (KWSM) is equal (in energy) to approx. 317.1 BTU/Sq.Ft./Hr, (BSH). Hourly "Sun-Pointing MIRRORS". Maintaining a current "Parabolic Folder" on ALL notes concerning "Parabolic". Member (# 16925, of A.S.E.S. for several years). Now revising to use Hardware Store "Aluiminum Chiney Flashing". Tested to be over 96.5 % "Solar Reflective".

/s/ Carroll H. (Sincere inquiries answered)

engineer mubashar on November 23, 2009:

Monica Jeenkins has asked about use of such reflectors for water heating.In my opinion answer is"yes" but we have to control the flow rate of water to control the water phase. Simply it is funtion of time and area assuming a turbulent flow.I think these systems may be used for pre-boiling of vegetables.We may use black chrome coated copper heat collectors for more hot water or steam but dont forget to add temperature and flow conrol through solenoid valves.

engineer mubashar on November 23, 2009:

i am a mechanical engineer and have a clear concept about solar energy conservation and its all current innovations.It is a nice and bright idea.I have conceived 100% same idea to make a prabolic mirror.Currently i am using another idea which will formulate a more better reflector.Let us build an energy coserved home a nd afterwards a such nation.

greathub (author) from Earth on October 27, 2009:

@optronics48: Good to hear that your project works. We, as human beings, need much much much more research before we can get so much advancement that we are able to produce high quality materials - at cheap price - to produce solar power.

optronics48 on October 26, 2009:

Thank you very much for a great project !!

I made one of wood for the basic structure, no cement. Used thin sheet metal for the curve of the trough and lined it with reflective gift wrap. Put a one meter long 32 mm aluminum tube painted black at the focus. Good construction will show a bright straight line proyected on a white sheet of paper when placed at the focus and aimed at the sun. All imperfections will make this line less straight and bright.

Mine was far from perfect, but even so, heated a liter of water ( a quart ) that was at 18C to about 90 C in only twenty minutes..burned my hand when touched the tube ! !

After having done this project, I ask myself..why do we use fossil fuels? Only greed of big bussiness and corrupt govts are the answer I can find.

Anyway, thanks again for a great project.

optronics48 on October 21, 2009:

Due to its water trough shape its quite easy to make a sun following device. Just put one end on the ground and the other at the angle of your latitude.Mount the whole thing on North/South line. This will only need to be turned on its axis to follow the sun, you can even rig a motor to do it full auto for you.Telescopes follow the stars this way.

I wonder if you put a black anodized aluminum tube, would it heat water more rapidly than the dish type parabola? As you say, just make it bigger to compensate for efficiency loss. Big dishes get kind of unwieldy without solid mounting, but this is a tilted water trough..a triangle with one end on the ground, very stable.

greathub (author) from Earth on October 02, 2009:

@ optronics48: just a drawing ..... not an accurate parabola.

optronics48 on October 01, 2009:

Is the yellow template on 7 an accurate parabolic curve o just a drawing ?

greathub (author) from Earth on September 17, 2009:

@ Charles:

Good question!

This cooker will work best at noon when Sun is directly overhead.

Charles on September 16, 2009:

I have read that one of the problems with parabolic cookers is that they must be focused often to follow the sun. How would you focus this one if it's made of concrete? Does this system is able to concentrate sun rays even if not aligned correctly?

Abuze on August 22, 2009:

Hi

This is very interesting information. i was looking for a cheap and easy design for a solar cooker and i think this is perfect.

see you when i,m done constructing. and thanks a lot for sharing, not many people would give out details of their works.

Karl_ on April 10, 2009:

Thank you so much for sharing...

I would like to point out that if you were to pivot your wooden template into the wet concrete mound, instead of plowing through it, you would end up with a parabolic mold. This is, of course, just a consequence of your excellent idea.

Regards.

greathub (author) from Earth on April 03, 2009:

@jazzheaven: You are right heat would be lesser with rectangular parabola. It would be concentrated on a single line unlike circular parabola that concentrates all rays on a single point. You can increase the surface area of parabola to solve this problem.

And don't forget to upload the images of the cooker that you build.

jazzheaven on April 02, 2009:

Hey G,

First of all great efficient thinking! I am figuring out a plan to construct a parabolic mirror (circular) bbq. The thing is that the proces of making a circular parabolic mirror is way more complex than the "rectangular" one.

I rather make a rectangular one like yours due efficiency THOUGH i'm afraid that I won't gain as much heat as with a circular one.

Am I correct to say that the focus line you get with a rectangular parabola is not as hot as with a circular parabola... since you actually collect the whole line into one point.

If that's not the case or you gain enough heat onto a baking stone your way I just make one shaped like yours...

Many thanks for your reply!

Kind regards,

JazzH

greathub (author) from Earth on March 17, 2009:

@ Bobby B!: If you are talking about Sun that "goes sideways in sky", something that happens in northern parts of the world, then you should try to tilt this model such that the longer side of rectangle becomes perpendicular to the incoming rays. This way you will get best results.

Bobby B! on March 16, 2009:

I love this! I'm gonna give it a try and get back to you. One question for now: you say this works best at noon, right? So what numbers should I plug in to the equasion for a lower sun?

Jay on March 05, 2009:

I am an engineer and have invested several months in methods of harnessing energy. The challenge is transforming one form to another depending on needs, The most generic energy currency appear to be electric which is readily made into heat, light and mechanical forms. Using heat we can create more biomass for fuel manufacture by extending growing seasons. Options exist to translate heat into mechanical. (operate a gennerator) Check out sterling motors. Best luck in your creative endevors.

Regards,

Jay

greathub (author) from Earth on February 05, 2009:

@ bergen: It would be a really nice idea.

Yes I did that too using specs in my childhood.

But I have no idea as to how one can make one on a large scale.

How about making something flexible and transparent for this purpose. e.g. using a lens-shaped transparent balllon-like material filled with a fluid that focuses light to a point.

bergen on February 02, 2009:

very good info. what about making the refector dish shaped? Have you done it?Have you used a flexable mirror material? Years ago we would use a glass flashlight lens to burn holes in paper also a magnifying len. Point is I am interested in heating liquid for heating in a cold climate. Small area, floor circulation.

I recently read and saw a piture of a 10' by 10' parabolic collector where a 2by4 held at the focus point burst into flame.

Also sun tracking would be nice.

I would like to hear you comments.

thanks

MrBurton on September 15, 2008:

okay this is easy, You can make a BBQ out of it, use it as a mold and place on a tracker with lighter material. The folks in the middle east have already used large parabolic boilers to heat water for steam instead of using fossil fuels.

nathan on August 31, 2008:

great, thanku

SANTOSHSHIVALE on July 22, 2008:

i need detail knowlage about how to make calculation of parabola and stand

Monica Jenkins from Northern Illinois, USA on July 07, 2008:

Hi there! I find this intriguing and your instructions to be very clear. Can you post some ideas about what we could use this for? Could we incorporate this into a way to heat water for instance?