This weekend, I designed my own solar grill at home using some of the unused articles and also some things were bought at nearby home appliance shop or novelty store.
Background for coming up with this crazy idea was that my android smart phone Motorola Defy was draining out of battery in less than one day with all radios enabled in it esp like mobile data, wifi, GPS. I needed a USB travel charger badly and bought a solar powered + usb powered (4400 mWh) which could charge universal devices like Camera/Ipod/Phone etc., on the go. Its output rating is 5.5V,500mA. It works just good in critical power needs during my trekking/camping. I had underestimated the solar power till then until it helped me really when I needed the most.
A few months back I had been to Lakshadweep islands where the sole energy for the whole island was Solar power. I was really amazed at the self sustained way to renew energy resource even for desalination of water using the temperature difference between the cold water of deep sea and the hotter surface water. Even the entire lighting was done by an array of solar cells.
I was looking at the ways to harness the this power in very small scale and came up with website called
GREENPOWERSCIENCE which does build the acrylic parabolic mirrors and extreme powerful fresnel lens which was well suited for my purpose but was not within the reach of my budget anyway. Then I went in search of ways to build my own parabolic mirror. Dan of the GreenPowerScience explains a lot of ways to make a user defined one with casting mortar and using it to prepare a cement mold. Grease the mold, then use 3 layers of fiber glass wool and polyester resin to bind them into a parabolic polyester dish. Well, this preparation was too tedious (but really economical on some scale if we plan to roll out many) but I wanted a better and faster way. The best suited idea for me was given by another youtube video which used the TV antennae that comes with the dish which is of parabolic shape to converge the KU band of TV signals into a focal point for better reception. So I bought a scrap dish from reliance big TV workshop near my place for 350 INR (Found a good quality dish in a stock pile of Defective LNB dishes) Its a 60 cm diameter dish which I bought with the clamps and bolts for fitting.
[If you are not into mathematics of conic section called parabola and want to understand why it works to choose this shape, please refer to
parabolic reflector and see here to
understand the theory and
check out the illustration]
Next step was to prepare a reflecting surface for the entire surface of the parabola. This was done by low cost Aluminum foil of food grade quality. This costs about 40 INR for about 7 mtrs X 30 cms. Not even 1/4th of it was used to cover the dish surface. I cut it into strips of regular sized rectangles (better to make trapezoids for easier coverity with very less wastage) to paste it with a child safe glue. The glue must be water based and it should be non-toxic as it might get heated and may fume in direct sunlight. Even with the application of tin foil all over the surface, the reflectivity is pretty bad about just 35-40% with the wrinkles and overlapping edges. The full sheet as such if stuck on flat surface would give about 55% of reflection. Also I
read about Mylar, Foylon and other reflective vinyl sheets which could be used for this but again cost issues exceeded my low budget project. I plan to upgrade to better reflective surface tearing down the current tin foil surface as it is not durable for long and the temperature tin foil reflection generates is very less and is insufficient to boil water. Using a mirror (glass based) would be optimal for me as it will be lesser initial cost but would require a lot of work to cut mirror into several hundreds of pieces to cover entire area of the dish.
I read somewhere that a square meter of earth's surface lit by bright sunlight generates can be equivalent to 1000 watts of power. So a 60 cm dish with good reflective surface will give above 560 watts of energy.
If you have concentrated a beam of light by magnifier lens to burn paper during your school days/for your curiosity then you can imagine the power of the parabolic concentrator.
After the reflective parabolic surface then the problem comes with the proper mount. Mount can be made anything and problem here is to get a grill at the focal point of the sunlight after the dish is mounted on any surface. It can be anything from an unused table fan bottom, a tripod etc. My initial attempt to use a 4 foot long flower vase stand went in vain as it could not withstand the entire weight as its center of gravity went outside the dish when mounted :P
After hunting more and more for unused items at home, I found a cradle (!) in which I used to sleep when I was a baby ;) An antique piece in rust but still standing :P Good thing is that its easily dis-mountable with 4 rivets at the bottom. I shall work on a good paint job sometime next week on it to make it a more durable.
It has got two hooks on the sides which helped me to put up the stainless steel round grill with a wooden handle on top of it with the help of small sized bungee ropes which holds it in place. Good thing about these ropes is that they got good tension retaining ability, they are insulators, and most important of all that I could vary the position and angle of dish for sunlight based on placement of hooks on the side rods of cradle.
Sad that there wasn't much sunlight today as it was rainy and gloomy all day long. So I couldn't test for temperatures it could go with direct sunlight. I shall update it soon after my next series of tests. :)
Things I bought for grill:
Parabolic dish - 350 INR
Aluminum foil + Glue - max 40 INR
Bungee ropes - max 30 INR each (I had some of them already for traveling on bike)
Steel grill - 140 INR
(You may also require a plastic ruler, blade to cut the foil)
Well within 600 INR of cost it is doable and it took me just 2 days with each day spending about 5-6 hours of work all alone on building this. I started building it on Saturday morning and completed on Sunday evening :)
Below are some pics that i took in building my solar grill. Will update more on the mirror upgrade that I plan to do and probably post a video soon of me cooking some good stuff ;)
Check out
some FAQs listed here if you have something in mind to start a project something like this.
Cheers!
Karthik
