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:
- Aluminium foil
- Bond (that can stick foil to the cemented surface)
- 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.
Step 2: Mark the midpoint of this line
Do this step carefully.
Step 3: Draw a vertical line passing through this point.
Carry out this step even more carefully.
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.
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.
You will end up with something like this:
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.
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:
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.
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.
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.