Building And Using a Solar Oven

[SmokerBill]

During my week long stay at the Imperial Dam LTVA near Yuma I met a fellow that typically had a couple of solar cookers going each day, one to heat water for domestic use and another for cooking food. I tried a full-size cupcake his wife made, which was excellent, and he showed me a section of pork loin he'd cooked. It looked great, but unfortunately, he didn't offer me a bite. 

Solar cooking made so much sense to me that I had to try it myself. For the last week here in Quartzsite I been busy building my own solar cooker. The first try was a bust, because I used an old corrugated cardboard box as the main material. Because of the corrugations, it wouldn't roll into the necessary funnel shape as easily as I'd have liked.

For prototype #2 I bought a few sheets of HD posterboard at the Dollar General, and it's worked out much better. I glued the three sheets of PB together into the correct size, glued on the reflective mylar, then formed it into a funnel shape.

Yesterday was its maiden voyage. I cooked a pot of fresh veggies- potatoes, cabbage, carrots and leeks. After 2 hours the potatoes on top were completely cooked, but after emptying the cooking container I found that the food underneath was not completely done. My guess is that the aim of the funnel was off somewhat and the sun's rays were more focused at the top of the container.

Today, after adjusting the angle of the funnel, I'm finding out how it cooks lentils (with a bit of chili, onion and garlic powders, black pepper and a couple of different dried herbs). To give them a jump start I covered them with simmering water. After 20 minutes they'd absorbed so much water that I had to add more water to keep them covered. I'll give them a couple of hours and see if they're done.

If anyone is interested in the particulars of how I built the solar cooker and the items needed let me know here and I'll pass on what I've learned. If you're curious, the total cost for everything, including the cooking container has been right around $15.

 

[SmokerBill]

OK, I just had to update. The lentils have been in the sun for less than an hour, and the liquid in the jar is actually boiling! Not a hard boil, but a steady simmer. And the temperture outside right now is 47 degrees! I'm totally amazed that I was able to make this work! So cool!

 

[Lowell]

If anyone is interested in the particulars of how I built the solar cooker and the items needed let me know here and I'll pass on what I've learned. If you're curious, the total cost for everything, including the cooking container has been right around $15.

I'm curious, lets see the particulars.  Thanks

 

[carson]

I'm totally amazed that I was able to make this work! So cool!

  Sounds/looks great.  I suppose your dinner time is around 3 PM.  How do you keep the clouds at bay ? 

 

[SmokerBill]

Haven't been too many clouds here in this part of Arizona. I'll get into how I made the solar cooker how it's used now.

The type I made is commonly called a solar funnel. It's made with a sheet of cardboard, lined with reflective material on one side, and sort of wrapped up into a caddywompis (uneven) funnel shape. When aimed generally towards the sun, it reflects the sun's energy onto the black cooking container, which absorbs the heat. The cooking container must be enclosed in another larger, transparent container. Some use a large glass jar or canister, others (like me) use a turkey-size oven roasting bag- which works well and can be reused.

Materials and Cost:

$3.00 -- Three sheets single ply, heavy duty posterboard
$1.50 -- 1/2 of a reflective mylar sleeping bag/ space blanket-  $3.00 total cost
$3.50 -- Can of Elmer's spray adhesive
$2.00 -- Clear packing tape
$3.50 -- Two Reynolds Oven roasting bags
$4.50 -- Glass canister (qt and a half?) with metal lid
$???  --  Flat black spray paint
------
$18.00 + paing

Overlapped and glued the 28" sides of the poster board sections together, to make a final size of 28" x 56". You can make it larger or smaller, but length has to be two times the height. I used duct tape (didn't have packing tape yet) on the glued edges for more support.

Once glue was set (overnight), I sprayed glue onto one side of the PB sheet, covering 1/3 at a time. Pressed on the reflective mylar. I found that the posterboard has a matte side and a shiny side. I think it sticks better to the matte side.

Allow glue to set overnight. Trim off excess mylar and wrap all four edges with the clear packing tape. This prevents the mylar from peeling off.

On the other side, make a mark along one of the 56" edges at the 28" point. Using a 7 or 8 inch pan lid, mark a half circle onto the edge, then cut it out with scissors. Tape around the cut edge.

With the cut semi circle facing you, mylar side up, carefully, form the posterboard so the two edges on either side of the semicircle cutout are overlapping about 1 inch. This forms the "sort of a funnel" shape.  Attach the edges together with whatever works. I poked three sets of two holes into each edge and ties with some scrap copper wire I had. Now you've just constructed your solar funnel cooker.

To use it, aim it towards the sky, generally towards the sun. It doesn't have to be pointing directly at the sun but good aim catches more heat, I think. I set mine to where I've only adjusted the position once in a three hour cooking sessing.

The cooking container has to be black. Supposedly ceramic doesn't capture heat as well as glass. I found a square glass canister at Beall's that works. Painted it with some flat black paint I had on hand.

Place food in container, placing it into the oven bag. Blow the bag up with air and seal the top with a twist of wire.

Set the bag/container onto a small wooden block (for insulation and to give it more height) close to the rear of the funnel.

That's about it. I don't take any credit for the plans, other than figuring out a way to make do with what I could get. The design originated at Brigham Young University. I think they even patented the design so it would be free for anybody worldwide to make. The free (after it's built) cooking heat can really improve the way of life in third world countries, where firewood is scarce and petroleum fuels nearly nonexistent.

But it's also great for RVers, I think. Put the food in it, and go about your business. It's claimed foods won't burn it it, so it's almost a set-it-and-forget-it sort of thing.

For traveling, you can un-attach the edges and store it flat, or roll it up and put it away somewhere.

there are more complex cookers that use an insulated box with a glass lid, reflectors around the top of the box. I think that style is better for baking breads, cakes and cookies.

Well, I think I about covered it. Time to check the lentils again.

Any more questions, let me know.

I forgot to add the link to the directions I used.

http://solarcooking.org/plans/funnel.htm

 

[SmokerBill]

  Sounds/looks great.  I suppose your dinner time is around 3 PM.  How do you keep the clouds at bay ? 

I eat when I'm hungry or when the food's done. No set time usually other than morning, early afternoon and evening.

 

[Olys45]

That's pretty sweet. I wonder what the lowest temp you can use it at?

Oly

 

[SmokerBill]

That's pretty sweet. I wonder what the lowest temp you can use it at?

Oly

Well, it was boiling water at 47 degrees today. I've read that with clear skies and being south of the 35th parallel, you can boil water when temps are below freezing.

My lentils turned out really good. Completely cooked. I just left it out there until about 3 oclock which was about 5 hours. I think the cooking container was in the shade for the last hour.  Again, I am thoroughly impressed with how well this simple tech works!

Why isn't its use more widespread???

 

[Wendy]

That looks very nifty. Can you demonstrate it one afternoon during the forum rally for those interested ?

 

[SmokerBill]

That looks very nifty. Can you demonstrate it one afternoon during the forum rally for those interested ?

Certainly Wendy.    I might even build another one to demonstrate how it's done.

 

[Olys45]

Well, it was boiling water at 47 degrees today. I've read that with clear skies and being south of the 35th parallel, you can boil water when temps are below freezing.

I guess being a few hundred miles south of Canada, I better wait until spring!

Oly

 

[SmokerBill]

It's in the winter it has problems in more northerly latitudes. The sun is just too low in the sky. At least that's what I read. Depends on the size and shape of the cooker too. If the shape is closer to truly parabolic, and the focus point hits your container it more efficient. When the sun is higher in the sky, the reflector shape is a somewhat less critical.

 

[JiminDenver]

Cool cooker Bill!

I really got into researching these a while back and nearly bought a premade oven but it was big and bulky. Then I started making one until someone asked me if it would attract the bears and coyotes sitting out in the open for long periods, so I've benched the idea for now. 

Here are some plans I found for some cookers if you are interested.

http://solarcooking.org/plans/

 

[SmokerBill]

Thanks Jim. That's one of the first sites I found, and was thinking about making one of the parabolic Parvati reflectors, but decided the way I went would be the easiest.

I have a hunk of venison thawed out for today's cook. Right now it's 21.4 degrees here in Quartzsite and supposed to reach about 40 by noon.    I'm curious to see how it works in even cooler temps than yesterday.

 

[JiminDenver]

Ok Bill, I gotta say I'm envious. I love deer meat and wanted to come to the Q so bad this year, Unfortunately Honey insisted on someplace warm like a 3rd world country. So we will be in Costa Rica here soon.
21* really? I thought it was warmer down there now. Good thing Honey doesn't read the forums (I think) or we will never get down there. 
I can tell you that for years as a tenter I would set our big black coffee pot in the wash basin on its side to heat the water. We didn't seal it and the basin isn't that shiny but in a hour the water was warm enough for bathing/ washing up and in two hours it was hot enough to add cold water for doing dishes.

 

[SmokerBill]

Jim, the temp is up to a balmy 37 now. I filled the cooking container with 1-3/4 large onions, quartered, 2 stalks of celery and about a pound of venison, all seasoned with black pepper and chicken broth powder (I use it instead of salt sometimes for a richer flavor).

Set it outside at 8:30, but the sun wasn't very bright in the sky. Checked at 9:30 and it was just barely warm. I readjusted it towards the sun, and now @ 10:00 the container is already too hot to handle. I should have sun-baked venison and veggies ready to eat by one o'clock.

Costa Rica huh? That sounds nice! Don't they make rum there???

 

[JiminDenver]

Rum? I thought all rum came from Puerto Rico. lol

This will be our first time to Costa Rica and I really know nothing about it. Honey showed the website to the resort a few days ago, said I want to go there in two weeks, it's up to me to make it happen. Luckily I was able to get the tickets from a miles card and the resort was listed on a time share site for four grand off. Still, for what it's costing I could make major mods to the trailer and have enough left over to pay down the loan some.

Considering the temps down there, I may have to revisit the solar cooker idea because the propane is going to have to stretch farther than it does here.

 

[jmugs]

Using solar is not only a good source for cooking and electric. We heat much of the water we use for bathing and dishes with the sun. Some simple heaters can be made as well.

I had a place near Bisbee, Az several years ago and it was nearly all solar. I used propane for my 3 fridges and had a gas genny for backup and heavy power tools.

I had 2solar cookers, both box style, one built for higher temps that would go over 400F real quick if I wasn't careful.

Bill, I like the cooker you built mainly since it will show others how easy it is to make and use effectively. Its an inexpensive teaching/learning tool, and just think, it might put some idle minds to work on some creativity. Look at you....there you were just hanging out in the desert and now you have learned more than when you got there and have put it to good use.How cool is that?

 

[SmokerBill]

That's right, it's coffee in Costa Rica. I knew it had to do with something good to drink!  Enjoy the trip.

One of the most important uses of solar in the poorer countries is heating water so it's safe to drink. Kills all the nasty bugs.

And by the way, it's lunchtime! I checked the food and the interior of the venison roast reached 195. Overdone by most accounts, but it's still tender and juicy. The onions on top actually browned a little, too. Only took 2 hours to cook (actually 3, but I'm deducting the hour between 8:30 and 9:30 because it had barely started to warm up in that time).

 

[SmokerBill]

Using solar is not only a good source for cooking and electric. We heat much of the water we use for bathing and dishes with the sun. Some simple heaters can be made as well.

I had a place near Bisbee, Az several years ago and it was nearly all solar. I used propane for my 3 fridges and had a gas genny for backup and heavy power tools.

I had 2solar cookers, both box style, one built for higher temps that would go over 400F real quick if I wasn't careful.

Bill, I like the cooker you built mainly since it will show others how easy it is to make and use effectively. Its an inexpensive teaching/learning tool, and just think, it might put some idle minds to work on some creativity. Look at you....there you were just hanging out in the desert and now you have learned more than when you got there and have put it to good use.How cool is that?

Pretty darned cool!  Tasty too.  I may build a box cooker, but this one works so well and is so lightweight and portable I don't really see the point, other than just to do it for fun.

I'd like to build a parabolic trough reflector and adds runs of black copper pipe through it to heat water (maybe a couple of 55 gal drums worth), then insulate the drums before it starts cooling down in the evening and use the heat for inside the TT at night. It would take a little plumbing, a heat exchanger and a small pump of some kind, but it could work.