Solar energy can be converted into other forms of energy, such as heat and electricity. In the 1830s, the British astronomer John Herschel used a solar thermal collector box (a device that absorbs sunlight to collect heat) to cook food during an expedition to Africa. Today, people use the sun's energy for lots of things.
Being an engineer, this got me thinking, so I did some research and found a number of useful resources. The most inspiring book was ‘Cooking with the Sun: How to Build and Use Solar Cookers’ by Beth and Dan Halacy. So, I decided to make a Solar Stove in June 2007, with this website as reference.
Otherwise, in my country, Indonesia, Dr. Muhammad Nurhuda, lecture from Physics Division of Brawijaya University had develop a Solar Stove too, but its different with mine. (Source: Kompas, 13 Maret 2008).
Why use a Solar Stove?
The heat energy produced by the sun is immense. In equatorial regions the solar radiation can exceed 1000 Watts/m2. That is equivalent to half the power of an electric kettle whenever there is good sunlight. It only takes 10 – 15 minutes to boil water on a solar stove. And it’s free, as long as you have clear blue skies! If not, you can boil it in 30 minutes. The material costs are about $10 per stove which with some sponsorship is feasible to raise, and they are fun to make.
Firewood, Kerosene and Health issues
The ‘Manual for solar box cookers’ published by Technology for Life, Finland quotes: -
"About 2000 million people, over one-third of the population of the world, are daily dependent on firewood as the source of their cooking and heating energy. They live in the tropics, in the most favourable areas for the use of solar energy. Every year the cutting of firewood results in the loss of 20,000 - 25,000 km2 of tropical forests (UNEP).
The use of solar cookers also brings with in important health benefits. Diseases spread through contaminated water cause 80% of the illnesses in the world (WHO). Heating water to the pasteurization temperature of about 60 0C destroys disease organisms. This temperature is easily achieved with solar cookers. Acute respiratory infections (ARI) are the cause of death for millions of children in the world each year. The large majority of these casualties occur in the developing countries as a result of polluted indoor air due to cooking over open fires in houses without chimneys or ventilation. This problem could be greatly reduced by using solar cookers, which are, of course, completely smokeless."
In Indonesia, kerosene was become primary needs for the source of cooking. Nowadays, the kerosene was rare and the government change it with natural gas. But, it's not renewable energy and it's still to expensive than buy kerosene stove and kerosene's.
How does a solar stove work
There are two basic methods of collecting enough heat from the sun to cook. These are commonly described as the ‘Solar Box Cooker’ and the ‘Solar Stove’.
Solar Box Cooker
The basic principle is to collect the heat by letting the sun light pass through a clear glass plate into a well-insulated enclosure. The light ‘trapped’ in the box and turns into heat when it is absorbed by the black cooking pot. The secret of a good Solar Box Cooker is to have good insulation with no air gaps and a good lid reflector to get the most light into the box. Cooking times are not that quick, but temperatures of 150 0C are possible.
Technology for Life, Finland has documented the Solar Box Cooker with great accuracy. For more information, click this link.
The Solar Stove uses a parabolic reflector to focus the sunlight to one point. This produces the effect of a massive magnifying glass. With an accurate reflector it is possible to get ‘times 100’ magnification. The reflector is aligned to point at the sun, and then the black cooking pot is placed on a grill at the focal point. Being black the pot absorbs most of the sunlight and creates sufficient heat for cooking.
Precautions for use of solar stoves
Do not look at the reflection of the sun at any time. Once the stove is in alignment with the sun, and the pot is at the focal point, then there should be no light scatter. If there is ‘stray’ light then the stove may need adjustment such that all the reflected light hits the pot (this will improve your cooking as well).
When adjusting the angle of the grill use thick gloves as the grill can get very hot.
The most important material in the stove is the reflective aluminum sheet. This I was fortunate to obtain courtesy of my ex. employer. The size of sheet was limited to 400 mm x 620mm as this fitted nicely in my suitcase. The aluminium is available from a number of suppliers, but the reflective qualities are important. I used 0.3 mm AnocoilÓ grade 710.33 which is 86% reflective and almost mirror quality.
The main enclosure is cut from 4 mm thick ‘Triple A’ plywood. An 8ft x 4ft sheet will make 21 stoves and only costs $5. A few other bits of wood are required to make the framework within the stove (sizes detailed below).
As the focal point gets very hot it is necessary to make the grill and grill support from metal. I used mild steel and painted it silver, but any metal will do.
Parts List and Technical Drawings. General assembly drawing
To view and print all the drawings together click here…
To download an Assembly Drawing as an AutoCAD file 49KB click here…
To download an Assembly drawing as a DXF (Drawing Exchange File) 94KB click here…
To download a CorelDraw 8 Assembly drawing 50KB click here…
To download an Assembly drawing as a PostScript file 52KB click here…
To download an Assembly drawing as a Windows Metafile 34KB click here…
710 x 570 x 4
Base support – long
Useful tools include: Drill, jigsaw, hacksaw, vice, wood saw, sharp ‘Stanley’ knife, tape measure, square, metal file and hammer.
Optional tools include: Grinder and welder.
Building the solar stove.
We split the work up into three sections. Manuel Reynaga was in charge of the metalwork, David Coe organized the lads (and one girl) in cutting the cardboard ribs, and I was in charge of the woodwork. We rotated the work, so they all had a go at each discipline. I was amazed how keen they all were to get things done. Once they saw the water boiling on our prototype they all wanted one!
I made up some templates for the sides and base, and cut them out using a 'jigsaw' power tool. The edges were filed flat. We then cut the frame parts to length and nailed the whole box together around the frame. See drawing WOOD for dimensions. Once the enclosure was assembled we made up the wooden SUPPORT at the base. This had the main purpose of holding the 16mm bar and grill in place. The support was nailed to the underside of the wooden box. To help align the stove with the sun we made a sundial by fixing a nail through the support at the edge parallel to the 16mm bar. By adjusting the stove to eliminate any 'shadow' of the nail it is easy to find the sun's location. See drawing GA for details.
The hacksaw, drill and vice came in very handy. The three main items are the BAR, GRILL and PIN. The bar pushes into the wooden base and is located in place with the pin. The grill is fixed to the bar with an M5 x 20 screw with a wing nut and spring washer. This allows the grill to be secure but also adjustable as the sun changes height. The bar and grill were painted silver to reflect more light. See drawing GA for details.
Once all the parts have been made they can be assembled into the box. The cardboard ribs should just drop in and sit flush with the base. If there are gaps under some of the ribs then it is probably because the slots in the ribs are not deep enough. Fitting the reflector is the final thing to do. We marked the reflector on 15 degree angles and then cut through with a very sharp knife leaving an area in the middle uncut. Take care of your fingers, we only had one accident! See REFLECTOR drawing for details. We then placed the reflector on top of the box and ribs and cut the edges to length. The reflector was then taped down around the edges, which produced an accurate focal point. We used shiny aluminium foil to tape the reflector in place. We found that the best method was to tape alternate edges first. This enabled us to push the other segments firmly on top of the first segments. It is worth spending time in getting each segment just right as this affects the focusing.
Maintenance and caring for your solar stove
When not in use, keep the stove in the dry. To store the unit in winter, remove the grill and grill support and turn upside down.
A dirty reflector will slow down the cooking times. Clean the reflector with a dry cloth or 'alcohol' if available.
Black pots work a lot better than silver pots. The pot needs to absorb as much light as possible and silver tends to reflect the light. Dull or 'matt' finishes absorb more light than 'shiny' surfaces.
Pots with close fitting lids keep the heat in and help the cooking process. Placing the stove in a sheltered area stops the wind from cooling the outside of the pot.
For Solar Cooking News Updates, please click here.