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Offline The Scientist

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How can I make a solar cooker?
« on: 02/04/2011 09:48:24 »
Hi all!

Is there a way to make a solar cooker using recycled materials?

Thank you very much!


 

Offline CliffordK

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How can I make a solar cooker?
« Reply #1 on: 02/04/2011 19:03:33 »
I think there are plans on making a solar cooker on the internet.

You might be able to use recycled aluminium foil, but it often gets pretty beat up.

Look for some good used mirrors.  Glass is relatively easy to cut, and so you should be able to shape your mirrors if necessary.

Another item you might look for are Fresnel lenses.  You might find them in either overhead projectors, or projection TVs.
 

Offline Jolly- Joliver

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How can I make a solar cooker?
« Reply #2 on: 02/04/2011 23:40:26 »
If someone through away and old solar panel that would be recycled.

But I think you mean solar concentration.

What do you mean by cooker? You dont mean oven do you?

I think you mean like a flat metal plate to cook burgers and stuff.

What's a good metal plate to use? If the metal is dark then it should absord the light better, someone else can probably tell you the best type of metal plate, Anyone?

Then you would just have to concentrate the sun onto it, but I think that might be a bit dangerous also, if you get in the way of the concentrated light, you could burn yourself, while cooking, so maybe it would be best to heat a rear section that you do not place anything upon or go near then, on the other side cook. Having something to seperate them would be a good idea also.

If that is what you want, that is. As for things to reflect the light, anything shiny could potencially, some-things will be better tho, magnyfing glasses, you could look out for one of the old ones they use to make for reading books.  I have seen them arround they are about the size of a laptop if I remember.

Anyway good luck and be careful.

 
« Last Edit: 02/04/2011 23:43:39 by Wiybit »
 

Offline CliffordK

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How can I make a solar cooker?
« Reply #3 on: 03/04/2011 03:25:21 »
As mentioned, Fresnel lenses are essentially flat magnifying glasses.  Our local computer recycler has a few of them out of overhead projectors.  But, a bigscreen TV Fresnel lens would be better.

A heat sink would be handy.  I was thinking of a black cast iron skillet...  or black cooktop grill.  However, Aluminium has better heat transfer capabilities than Iron.  That may or may not make a difference, or would be something that would be easy to test.  You might want to be careful of the surface under your skillet though.

It is very difficult to burn your hand with a magnifying glass for 2 reasons.  Usually when you put your hand under the lens, it is slightly out of focus.  Just enough that you don't get the full brunt of the concentrated sunlight.  You also don't keep your hand at the focal point for long.  But, the bigger you go, the more caution you must take.

I have a junk 10' satellite dish out back.
Line that with foil, and it would be better than a solar micro-wave.   ;D

As far as solar-electric.  The efficiency is only about 10%.  If heat is the goal, then direct/reflected heating is far better than making electricity, and then heating with the electricity.
 

Offline Jolly- Joliver

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How can I make a solar cooker?
« Reply #4 on: 03/04/2011 16:19:04 »
However, Aluminium has better heat transfer capabilities than Iron.

I think your talking about the metal to be heated.

For shiny materials to concentrate the light wouldn't low heat transfers be better? They I presume would'nt absord as much and so would reflect more light and heat, I'm not sure which materials would work best for that tho.

If you did use aluminium, as the metal to heat the food, do you think it would be a good idea colour it black, to increase it's light absorbtion? If so what do you think we be a good way to colour it?
 

Offline CliffordK

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How can I make a solar cooker?
« Reply #5 on: 04/04/2011 07:33:35 »

If you did use aluminium, as the metal to heat the food, do you think it would be a good idea colour it black, to increase it's light absorbtion? If so what do you think we be a good way to colour it?
Yes...  Dark & Black is best for the absorbent part.  Reflective material including possibly aluminium foil for areas you don't want to absorb heat.

My problem has always been to keep my pots and pans from turning black!!!!!!!!!!

I would encourage NOT painting any parts exposed to your food.

You can find many dark Teflon coatings.
Also consider dark colored ceramic coatings.

And...  if you are more adventurous...  a little grease, and a good fire, and you can make anything black (outside, of course)!!!!  Well cooked grease might be sufficient even without the fire.
« Last Edit: 04/04/2011 07:35:10 by CliffordK »
 

Offline Jolly- Joliver

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How can I make a solar cooker?
« Reply #6 on: 04/04/2011 11:46:31 »

If you did use aluminium, as the metal to heat the food, do you think it would be a good idea colour it black, to increase it's light absorbtion? If so what do you think we be a good way to colour it?
Yes...  Dark & Black is best for the absorbent part.  Reflective material including possibly aluminium foil for areas you don't want to absorb heat.

My problem has always been to keep my pots and pans from turning black!!!!!!!!!!

I would encourage NOT painting any parts exposed to your food.

You can find many dark Teflon coatings.
Also consider dark colored ceramic coatings.

And...  if you are more adventurous...  a little grease, and a good fire, and you can make anything black (outside, of course)!!!!  Well cooked grease might be sufficient even without the fire.

Also I think if it wasn't dark it could reflect the concentrated light. but ofcourse the part that is being heated isn't the same part you cook on. so it's just a case of colouring the area to take the light concentration.

As an automated system, that electronically seeks best position, they could be a good type of solar BBQ in the right conditions, with none of the issues related to charcoal. The wether being the only issue. But you could make a duel system that heats the metal underneath for times when the sun is not out.

That could make a good comercial product, actually. "ENVIRO-Q".

 

Offline briligg

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How can I make a solar cooker?
« Reply #7 on: 06/04/2011 19:02:49 »
We have a solar oven, which works wonderfully. We got the plans from www.solarcooking.org. It's great because you just put your dish in it, and leave it to cook slowly. All you have to do is return briefly every half hour or so to turn it a bit so the sun hits it full on. The chances of something burning are almost nil, meat turns out super tender, beans turn out really soft (if you presoak them). But we are also looking at making a grill.

You might have an easier time finding bulk magnifying glasses, rather than a Fresnel lens. I used to go to a surplus store that sold 4 inch ones for super cheap, i think they only cost 50 cents. It would be bothersome to assemble a bunch of them so they are loosely focussed on the grilling surface, but perhaps the right tricks could make that a lot easier. Like maybe if you could find bulk lenses that fit nicely into the outer ring of a mason jar lid. I remember seeing a youtube video of someone cooking using a parabolic dish no larger than the little satellite dishes used these days (which i think is what it was, covered with mylar or something). A piece of paper stuck in the focal point burst into flames almost instantly. It seems that you don't need a large focal surface to get good results.
 

Offline Geezer

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How can I make a solar cooker?
« Reply #8 on: 06/04/2011 22:08:30 »

 beans turn out really soft (if you presoak them).


Mind how you go with the beans there. Some types of beans remain a bit poisonous unless you cook them above a certain temperature.

http://en.wikipedia.org/wiki/Phaseolus_vulgaris#Toxicity

"However, lower cooking temperatures may have the paradoxical effect of potentiating the toxic effect of haemagglutinin. Beans cooked at 80 °C (176 °F) are reported to be up five times as toxic as raw beans.[2] Outbreaks of poisoning have been associated with the use of slow cookers, the low cooking temperatures of which may be unable to degrade the toxin."
 

Offline briligg

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How can I make a solar cooker?
« Reply #9 on: 07/04/2011 04:12:10 »

Mind how you go with the beans there. Some types of beans remain a bit poisonous unless you cook them above a certain temperature.
Wow, i did not know that. But the oven gets above 100 C, the beans boil. Usually for at least a couple of hours. We have yet to get a thermometer for it, but my guess is it gets to about 120 - 130 centigrade. (I don't know what that is in fahrenheit, sorry.)
 

Offline Geezer

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How can I make a solar cooker?
« Reply #10 on: 07/04/2011 04:34:14 »
When it's boiling, the temperature cannot exceed 100°C (or a bit less if you are at a higher altitude) but if you make sure it really does boil for at least ten minutes, you should be fine. However, a thermometer would probably be a good investment. A couple of doctor visits will be a lot more expensive!
 

Offline briligg

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How can I make a solar cooker?
« Reply #11 on: 07/04/2011 23:45:34 »
When it's boiling, the temperature cannot exceed 100°C (or a bit less if you are at a higher altitude)

Sorry, i meant in the air around the cooking pot.
We are at 7000ft (2100m) so i guess the boiling point is a bit lower - i should look that up. This is a fairly small town, searching locally for an oven thermometer turned up nothing, and even the local version of ebay has an extremely limited selection.
 

Offline briligg

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How can I make a solar cooker?
« Reply #12 on: 08/04/2011 00:00:20 »
The solar oven, during its debut. We usually use the corningware casserole dish inside. It is white, but that doesn't really seem to make much difference. We were going to do something to turn it black until we realized everything was cooking just fine the way it is. Its heavy glass lid helps pressure build up inside it, which is helpful.

« Last Edit: 08/04/2011 00:02:57 by briligg »
 

Offline Geezer

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« Reply #13 on: 08/04/2011 03:11:33 »
Oooo! Very impressive!

Yes, at 7000 ft it will knock the boiling point down about 7°C. You could try heating a pressure cooker with it to compensate for altitude although you might have to make the pressure cooker less reflective. I wonder if a layer of soot from an open fire would do the trick?
 

Offline briligg

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How can I make a solar cooker?
« Reply #14 on: 08/04/2011 05:33:14 »
Yes, i've thought about pressure cookers. This oven isn't the right shape though. I haven't seen any pressure cooker that would fit inside, they are too tall.

The open fire idea sounds good. We could easily coat the casserole dish that way. I have also toyed with the idea of coming up with a bungie-cord type of setup that would strap the glass lid more tightly to the casserole dish. That would take some trial and error - would the cords degrade in the heat, would the pressure be significantly improved, we'd have to experiment.

Maybe it would be better to simply put something heavy and black on top of the lid.

In the photo we still have foil on the inside of the oven, but we later decided a dark colour was a better idea. We'd heard conflicting opinions on that.
« Last Edit: 08/04/2011 05:34:56 by briligg »
 

Offline Geezer

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How can I make a solar cooker?
« Reply #15 on: 08/04/2011 07:20:43 »
Yes, i've thought about pressure cookers. This oven isn't the right shape though. I haven't seen any pressure cooker that would fit inside, they are too tall.

I really don't know much about this stuff, so don't take any of my suggestions too seriously, but would the height of the pressure cooker make much difference? We have one that is about a foot in diameter, and maybe ten inches in height. Would something like that work?
 

Offline briligg

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How can I make a solar cooker?
« Reply #16 on: 08/04/2011 17:29:30 »
would the height of the pressure cooker make much difference? We have one that is about a foot in diameter, and maybe ten inches in height. Would something like that work?
No, the oven is only about 4" (10cm) high at the front, and maybe 6" (15cm) in the middle. You can't see it in the photo, but there is 1/4" plate glass covering the top face of the oven, which is screwed in place. You can vaguely see the outline of the oven door on the far side of the oven, where my thumb is. That's why the air around the casserole dish gets so hot, and we need a proper oven thermometer to go inside it. The wooden oven enclosure contains 1" fiberglass insulation on all sides. The outside gets a bit warm to the touch when we're cooking, but that's all. The side edges of the glass are raised 1 mm or so above the frame. Other than that, there is very little air exchange between the interior and exterior. The door has a rubber seal.

If it wasn't for the oven being enclosed and insulated, the temperatures it could reach would be a lot lower. I imagine it could still be practical, but only for much smaller amounts of food. This morning at 10:30, I put a 2.7 kg chicken on to cook, along with 1 kg of vegetables (whole carrots and 2 whole heads of garlic - no water, the chicken juices are enough), all in the casserole dish. The chicken will be ready about 3pm - so roasted the skin on top will be paper thin, and the meat will just fall apart. A few days ago, i made a lasagna that was baked in the pan under the casserole dish in the photo - i bet it weighed 4 or 5 kg when it went in. I didn't put it in until 12:30, and it was ready at 4:30 - In fact i left it too long and the cheese on top got too crispy.
 
 

Offline briligg

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How can I make a solar cooker?
« Reply #17 on: 08/04/2011 17:48:38 »
We based the design on this man's oven:
He is in southern Ontario. There are several videos of him using this oven to cook in late winter, when the ambient temperature is below 0 Celsius. We adjusted the angles of the oven to be more appropriate for our tropical location, and the hardware details on ours aren't as refined. There is an earlier video where his first version of the oven failed because the high-density foam insulation he used melted. Fiberglass will hold up under much higher temperatures.

I should say i had very little involvement with the actual building of our oven. I was the one agitating for one, and i found the design, and i held things and stuff while my husband Aldo built it. And we didn't have detailed plans, basically we had a rough drawing from solarcooking.org, and Aldo mostly reverse-engineered based on the above video. People have asked me for plans, and i have stated that i am going to get around to drawing them up, but it isn't a simple project unless you already have carpentry experience.
 

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How can I make a solar cooker?
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