Solar cooker

Sorry, I'm no help...but I've been thinking about building a solar kettle. I shall watch the thread with interest.

( Not to mention the KrisDel ^TM raster scan solar toaster... )

Good luck

Del

Gloss white paint on a smooth surface will reflect more than enough light, if the reflector is correctly shaped (focused).

As its long wave infrared you're more interested in reflecting, I seem to remember the the rflection from copper or brass coloured surfaces are much better than from a 'silvered' surface.

When I was designing an infrared thermometer in the 70s we played with an umbrella as a reflector!! and it worked extremely well!!

Remember its not visible light you want, so ignore the problems with wrinkles and with bright shiney foil, go for a nice copper colour.

Incidentally, the umbrella we played with turned out to be extremely good for focusing sound waves as well, we could put a microphone where the handle is and point it and record at a distance what was being said... Our boss at the time was not amused with our antics!!

John.

I like this. I am imagining a short handled retractable type. perhaps breaking the elbows to allow a more collapsable/variable focal range. Could then, a lens be mounted at handles end to increase focusing ability?

ooh, I do like this. I would enjoy tinkering this project. But alas,......

.....Oh waiter, waiter! Might I order a pair of 48hour days, please? Mine are all too short!

cr3

This is a good new input that copper or brass coloured surfaces are better than silvered surface.

Thanks

Unfortunately, what they're really talking about is that polished gold is a much more effective reflector of IR than aluminum or silver.

Look on the Edmund Scientific web site and check out the photo of their solar cooker. It's cheap and effective, and I'm sure you could make one up using their design.

Whoops! Did I just type what I was thinking?!

Much more practical and useful invention over the non-hydrocarbon automobile.... thingamabob.

What dispersement requirements/expectations do you have for the heat generated?

I think u can make first parabolic reflector in pure aluminium.after complet fabrication electropolishing can give u about 85% to 90 % reflectivity.

-Tushar patil

In my opinion, the presence of wrinkles is unavoidable, but not so detrimental for the performance of the reflector (unless the foil appears extremely crumpled).

Metal depositions on plastic foils may however present a very good performance in terms of solar reflection, even better than an aluminium foil. In fact, it is not only important how much energy is reflected, but also the specular rate of the coating (that is, the fraction of the totally reflected energy, which is specularly reflected, whilst the remaining fraction is diffused).

For example, looking at some data I have at hand, I can see that Aluminium tape may have a reflectance of 75%, and 50% of this reflection occurs specularly. Polished aluminium surfaces may present a much better performance, as total reflection may reach 90-95% of the incident energy, with a high specularity rate. An aluminised Kapton tape may reflect 88% of the incident solar flux, with a high specularity rate also (95% of the total reflected energy). Of course, metal side must be placed externally, otherwise the reflection falls to sensibly lower values (50-60%).

I honestly am not aware of the behaviour of glossy white paints, I have never used them in my job.

Finally, the above figures are referred to the full solar spectrum, from visible to IR wavelengths. For it is true that, for common applications, we use IR devices for temperature limit reasons, but the largest part of the thermal radiation of the Sun occurs in the visible wavelength range

It would appear that you somehow need to test all the excellent suggestions in some way and see which reflector material works best with sunlight.....or use an infra red source to standardize things.

Once you have decided, I would still suggest that you build it much larger than needed and use some shading to control the temperatures achieved.

The use of a simple visible spectrum laser as the heat source, will allow better alignment as you can actually see the light, and with a bit of luck, enough will be reflected still to see.

Do not make your focus too sharp as that point may overheat, and use a metal like Aluminium that allows the heat to get distributed fairly evenly for the receiver/cooker part, Matt black of course!!

I will follow what you do and wish you well.

One further point, what you are doing can be very dangerous for your eyes, make sure that you have good shades on that will reduce the heating and light effect to your eyeballs, maybe even Laser safety goggles would work.....but check up yourself first and always USE THEM!!

Which is why a laser pointer will be useful to you when setting up and adjusting, not so hot!!

Commercial lighting fixtures commonly use parabolic reflectors, these are often made from pre-anodised aluminium with a bright finish. If you have any metal spinners in your area they might be making these.

pretty much any decent reflector will work, you just need to size the diameter of the parabola accordingly.

The foil should be fine, we do this with the scouts all the time.

These might give you some ideas.

We we talking about cooking food? I was under the impression this was a discussion in regards to a super cooker for unpasturized titanium alloyed uranium, that we were trying to keep off the grid.

I must have watched too many James Bond/Austin Powers movies...

I just KNEW the umbrella was a good idea!

I would think that it is also important to use a non-reflective material in the pot to absorb the maximum benefit of the infrared energy.

Why not make the dish out of thin Aluminum plate. Press it to shape. then polish the inner surface. Have polished Al to mirror surface.

Good inputs for me to try. I will try Kapton tape to startwith. I do not know if I will be able to try Brass or copper since this may not be available in the form of adhesive tape which I can simply stick on the surface.

Copper tape is available from companies who supply EMC screening materials.

Hello rsalaskar

i was scanning my old mails when i got this site and was wondering how i missed it , as my neibhour was attempting to build a solar heater , i thought to make a note of it, he used a old scrapped dish antenna and bonded small glass mirrors after pressing very fine foil of brass on the surface and possible bonded with good adhesive , these tiny mirrors he got it from fancy gallery shop ,7-12mm diameter ,0.6mm thick round mirrors he bonded throught inner surface with equal spacing and also exposing back glossy brass surface say not very precise 30%, light And heat concentrated on 8l cooker pan coated with carbon black with high temperature resin , broad daylight did provide him good heating and almost got boiling within 4/5min for 3liters of water. i have read comments posted by members it is clear to me by now gold platting to reflect IR light better than any other surface

Thanks Vikas, I am trying the same, only a smaller dish of about 24 inches diameter. I have ised chrome plating as well as metalised polyester tape successfully. This works well.

I am trying to locate now the maker of these reflectors so that I can get these cheaper and reduce the cost of making these reflector.

My idea is to distribute these in a village(about 100) on experimental basis at a cost less than Rs. 500($13) each to use as domestic solar cooker. The cooking needs about 1.5 hours with this reflector.

Thanks for the input.

How is "Sun following" catered for, are they on some sort of base that allows turning without spilling (and the dangers of burns!). I would be interested in learning how you handle that.

If they are used in a sub Tropical or Tropical zone, then the Sun passes almost overhead at noon and the pot might obscure the Sunlight, if farther away from the tropics then you need to follow the Sun's position as it moves around. How have you made this possible for a primitive folk to understand and use.....1 1/2 hours is approximately 23° of movement of the Sun itself around the equator....

There are two designs.

In the conical cooker the sun tracking is not required continuously. It takes about 1.5 hours for cooking and once the cooking vessel is kept at focus in the cooker, you do not need to focus it again. The cooker is on a simple stand and initial focusing is done using a device with a bolt and washer, the shadow of washer on bolt to be in marked area.

In the more economical reflector that I am trying to design using TV antenna dish of 60cm diameter, you are right, I have yet to finalize a sturdy mechanism though frequent adjustment is not required.

Thanks for the reply.

When the project is finalized etc., I would appreciate seeing a web page with Pix of the cookers in action, I am sure I am not alone either!!

I would think of designing a mechanism based on spring powered rewinding clock not exactly for time tracking with respect to sun positioning around the horizon , just positioning for economic part , they have enough energy(power) to position the whole assembly with more gear added for torque and screw mechanisms for further alignment to gather maximum possible sun energy and facing the sun most of the time throghout the day. this is quiet cheap and also operatable by rural folks , other way of complex electronics and controls can do better but to power them electrically plus the complexity adds up the costing

Sounds completely feasible to me.....

The flexible screw type adjustments used on telescopes might be of use here.

I have been working on another project that utilizes a flexible screw and have found that there are a large number of springs that have sufficiently close dimensions to fit standard nuts. So for economy. One might use a screen door spring, and a 1/2" x 13 TPI nut, with a kitchen cabinet knob inserted in the other end and tack soldered in place as a focusing device. Similar to this: