- Renewable & Alternative Energy
How to build a solar stove
Double disk solar stove
Solar stove: The concept
The core of my solar stove is an old satellite dish. If you cover the concave surface of the dish with highly reflective material, the rays of the sun is reflected towards a focal point (where the receiver component of the TV dish used to be). The heat at that point is high enough to cook/fry food placed in a black pot (which absorbs heat). It’s like focusing the sun on the pot using a massive magnifying glass. The concept is not new at all and many DIY guys have done this. However, my stove is quite different from the rest in basic construction - to such an extent, that it is easy to use on a regular basis. This type of solar stove is also known as a "parabolic solar cooker."
The primary disk
I was lucky to get a fibre glass dish in perfect condition for the primary disk. It is bigger (90 cm x 110 cm) (35 inches x 43 inches) than the ones used nowadays, which means more heat as well.
a. Sanding: Remove all the attachments and try to get the surface as smooth as possible (sanding). The smoother the surface, the better the focusing of the rays on one point.
b. Reflective material: Now cover the concave area with a shiny, reflective material. I used aluminium strip with adhesive on the back. This works just fine, but does have the tendency to lose its shine. Then I just polish it with metal polish and it’s perfect again! I do have another dish as well (see below), where I used strips from the highly reflective emergency blanket made from Mylar. For this, however, you have to add the adhesive yourself.
c. Pivot points: I made two flanges and attached these to the sides of the dish (middle)(no. I in image). These flanges then serve as the re-enforcement through which bolts will be inserted and coupled to the frame, as in the picture. The dish pivots (north-south) on these two bolts.
The frame of the solar stove
The frame of my solar stove is the supporting structure which holds everything together. The dish pivots north-south in the frame and the frame also makes east-west alignment possible. It also provides for the structure onto which the pot will be placed.
The width of the frame:
This is determined by the width of the dish with both flanges attached - 98 cm/39 inches in my case.
The length of the two vertical timber beams:
This is determined by two factors:
a. Where the pivot holes should be placed in the vertical beams: Make sure that the disk does not touch the horizontal beam at the bottom when pivoting and mark the pivoting holes in the frame (68 cm/26 inches from the bottom in my case).
b. The focal length of the dish: The focal length of the dish is how far the focal point (focus point) is from any point in the concave side of the dish. This you have to get right, for that is where the pot will have to be placed. Direct the dish to the sun. Then take a piece of cardboard and search for the point where the concentrated heat is at its maximum. (Watch the smoke!) Measure the distance from the middle of the dish to that point (60 cm/24 inches in my case). NB: Always wear shades/sun glasses when working with the dish in this way. Add this length to the pivot holes in the vertical beams, as well as another 10 cm/4 inches (the reason will become clear later) and you have the length of the vertical beams (130 cm/51 inches in my case).
Support for preventing the frame from falling over:
Obviously the frame will need some structure to keep it upright, but not prevent readjustment to track the sun. I came up with the detachable supporting structure in the picture (no. 2 in picture). The big wing nuts are for getting the structure level.
The Structure for holding the pot in place
The structure holding the pot has to be strong enough to hold a pot filled with food and such that the pot will not fall off when re-adjusting the structure towards the sun (no. 3 in picture). The diameter of the circle is 23.5 cm/9.25 inches and my black pot fits nicely inside the circle and cannot fall off when the structure is re-aligned.
The arms of the pot-holder fit into slots at the top of the vertical timber beams and can slide to either side. As the sun moves, the focus point shifts as well and instead of re-adjusting the whole structure every 15 minutes to track the sun, only the pot-holder can be adjusted (by sliding it left or right in the slots) to get the focus in the middle of the bottom of the pot again. You can keep on doing this for about 40 minutes and only then re-adjust the whole structure to face the sun again.
The secondary dish
As you can see in the picture above, I added another, smaller dish (60 cm x 72 cm/23.6 inches x 28 inches) to my solar stove – this one for focusing on the side or the lid of the pot. This second dish is particularly handy when it’s windy and a lot of heat is lost to the environment.
Solar stove references
Operating the solar stove
1. Start by aligning the structure in an east-west orientation, facing the sun. The shadow will help you to get it right.
2. Then make sure everything is level.
3. Put your pot in place, in the middle of the structure.
4. Then swivel the dish until the concentrated focus is in the centre of the bottom of the pot. NB: Put on you sunglasses before doing this.
5. Keep the dish in place with an adjustable rod/pole. I use an old mop handle (no. 4 in image).
6. Every 15 minutes slide the pot holder (in the slots) slightly to one side until the focus is back to the middle of the bottom of the pot.
Unfortunately parabolic solar stoves are not for sale at Amazon, but you can get them elsewhere, like at Cantinawest.com. Solar box stoves (also known as solar box cookers) are available at Amazon - like the . We have many years of experience with them as well. Using the solar dish stove in combination with the solar oven is the best possible scenario you can get if you are into solar cooking, for the dish cooker is quick, whereas the solar oven is perfect for thawing, warming your food or slow cooking. All American Sun Oven