Solar ovens Q and A. Mostly Q. :P

[XERTYX]

So I was watching jimindenvers channel for the first time the other day. Quick shout out this guy has a brilliant mind.

In one video he was demonstrating 2 of his solar ovens. I have heard of them before but never seen one in person and had never seen one on a video.

When I was younger and the internet didnt really have videos much to speak of I got into the hippie mindset and looked through a lot of blogs about minimalist living and so forth. And found a few articles on them. But the consensus was they were incredibly difficult to use. Expensive unreliable and inefficient. 

But Jim cooked up some food in a few hours for free from rays of sunshine. So I went thru his link to amazon. Pump the breaks. Outta my price range unless it also serves me and cleans up after itself. 

I got to browsing the interwebs and found some DIY solar ovens. The simplest one was 2 cardboard boxes from home depot insulated with newspaper and a sheet of glass as a lid. It achieved 200° if you believe the poster.

Then i found another guy. He built one out of particle board, aluminum, formaldehyde free insulation, velcro, and a spare sheet of window glass. 450° temps in California summer. With thermometer proof and multiple videos using it over the course of several months.

So I wanna build one. The kid with the cardboard oven had it on a lazy Susan swivel so he could follow the sun without disturbing the contents too much. A good idea.

This is my idea. A wooden box inside a wooden box filled with spray foam expanding insulation (unless that's toxic) the lid at an angle and the inside sprayed down with high temp black grill paint. A hinged plexiglass lid with rubber gasket and latch. 4 plexiglass panels one the sides treated with mirror effect spray paint as reflectors. Sitting on a lazy Susan swivel.

I havent found anyone giving specs in their DIY videos. Just approximations. The angle of the lids look to be around 40-45° the reflectors no idea on the angle. I suppose I'd have to play with it a little. And see which angle works best. But I'm stuck. The door window would need to be fairly large and obviously id like the biggest reflectors but an 8X10 piece of plexiglass is fairly cheap. I'd think the reflectors would need to be oriented longways for max sunlight but then that would only have 8" along each side of the oven and there would be gaps. 

Also how deep should it be inside to cook chamber? I'm thinking the smaller the better. Less air to heat up, but also less thermal mass in the way of black paint to help soak up the light energy. 

Am I over thinking this or underthinking it?

Have you built one yourself?

 

[highdesertranger]

I can't help you on the build in any way. but I can tell you that Jim knows his stuff with these ovens. I have eaten ribs and corned beef that he has cooked in his ovens both were excellent. he has at least 3 different ovens maybe 4 or 5 I am not sure. he should be around Quartzsite this winter. perhaps if you wait until then you can see his and go from there of he might see this thread and chime in. in fact I will PM him and ask him to check it out. highdesertranger

 

[XERTYX]

Thanks HDR. I'd assume trial and error would be my only way to work thru it but like you say Jim knows his stuff. I'm sure there is a "perfect" angle for the tilt and reflectors. Close should give decent results I'd imagine. I'm not smelting copper in here. Just like to roast taters, meats, maybe dehydrate jerky using the sun. It's pretty cool I think. And way better for the planet than any other cooking method since I dont have a geyser or active volcano in the yard.

 

[highdesertranger]

if you were smelting copper then I could help. LOL highdesertranger

 

[jimindenver]

You guys are making me blush. lol

Here is a page of plans for the various types of solar ovens and cookers.

http://solarcooking.org/plans/

I am plan on making more solar cooking videos here soon. I want to show more than ribs and corned beef. Most of the time the ovens are used in a more mundane way everyday. I use them for frozen burritos, pot pies, TV dinners, left overs, even heating up the dish water. Yes there will be fancier meals, cakes, breads, etc. I just want to show that they are useful as a regular part of my cooking routine.

Three days ago it was three racks of baby backs, corn on the cob and pineapple upside down cake. Yesterday I dropped a frozen tray of On Cor chicken parm patties. After a few hours they were bubbling hot and ready to eat. Right now I have four quarts of water in a oven heating up for dish washing. It will be 190 degrees by the time I pull it out. I keep a ladle with the cooker if anyone wants coffee, tea or Ramon.

 

[blars]

I think the glass needs to be UV transparent, which is why plexiglass is not used. (Most plexiglass is not UV transparent.) Some glass has UV blocking coatings.

 

[XERTYX]

Hmm. That's something I hadnt considered. Maybe when I go to Lowe's I'll carry a TV remote with me. I dont know the wavelength of UV and TV remotes are infrared not UV but I do know that a cell phone camera can see IR light. A handy trick to use to check your clickers battery. Try it. Point your camera directly at the remote at point blank range and press a button. You'll see a little purple light flashing unless maybe your remote has a filter on it. Seriously though try it.

 

[eDJ_]

My first one was made out of a cardboard box and glazed with plastic wrap held in place with cellophane tape.  The reflector flap was a piece of cardboard I had painted with white liquid glue and pressed against the dull side of a sheet of
aluminum foil which made the reflector.   The corrugation ran from side to side or right to left across the narrow side. (very important)  

The bottom narrow end of it was scored to work like a hinge with no foil glued to it.  This tab was glued to the top of
the box oven and reflect the sunlight down thru the plastic wrap. 

To the side of the flap when it was closed down I glued a second small piece of cardboard with the corrugation running side to side to match the reflector flap.  Then a thin but stout piece of wire was cut to have a 3/4 inch 90 degree bend at one end to the left.  The flap was lifted up to about a 45 degree angle and the wire  (where the 3/4 inch bend was stuck into the small piece of cardboard to hold it in place)  marked so it could be bent to the right at a 90 degree.  (kind of like a straightened out "Z"   Then that upper end was placed into one of the corrugations to hold the flap at a 45 degree over the plastic wrap glazing. 

I had some old styrofoam insulation about 1 inch thick that I lined the sides and bottom of the box with.  It too had aluminum foil glued to it with the shiny side facing inward. 

This box had a lid that sit on top of it,  I think it had computer printer paper in it when it was new.  

So all I had to do was sit the top over the box with a baking pan or muffin pan in it 

My first try with it took place at 10 am one sunny morning and by around 1:30 pm I had 6 blueberry muffins from one of those just add water and an egg mix bags.  

Next time I was by a Dollar Tree store I looked at the frames and found a rather large one with a piece of plexiglass that was about 1/16 inch thick.   So I removed the plastic wrap and glued in the plexiglass and found it to work much better on the second try.  

I used it some time heating cans of Denny More Beef Stew,  baking small frozen pizza's and toasted cheese sandwiches.

Must say it was fun but time consuming.  You know the saying...."a watched pot never boils",  well build yourself a solar oven from a box and you'll understand this wisdom shortly.

I looked at the sunflair oven and some of the others and thought of the room it would take up.  Even thought of designing a kitchenette around it that could be moved outside the Van into the sun to cook and bake as an outdoor kitchen.   I gave up on all of that.   I carried the cardboard box solar oven with me on the floor most of the time I went camping back then.  I found I could stow some bulky food stuff in it to get double duty with it.  

I wound up giving it away after I had used it some.  I found I could buy baked goods at the store to take with me and heat cans of food on the stove top easier and in less time.   I didn't go camping to cook all day as I wanted to fish or go swimming or hiking.  I could have stayed home and cooked.  If I had been full timing I may have thought differently.

It was much like this:

 

[MrNoodly]

I don't have the patience for solar cooking, nor the mindset for starting to bake things well in advance of being hungry.

 

[Dingfelder]

I got one of those glass tube ones. Excellent reviews on it, but it needed more unfiltered sunlight than I could get. Too many forest fires meant our skies had too much ash in the air even when fairly bright and the temperature was blazing. I don't think I ever got temps over 113 even in the most direct sunlight we had, and temps at or near 100. Just a heads up to others that you need more than sun to work at least one of these things ... in some conditions, anyway. I gave it numerous tries and will again someday ... maybe soon actually, as our weather is pretty good lately.

 

[jimindenver]

What brand of vacuum tube cooker is it? I was loaned A GoSun for my seminar at the RTR and it was getting hot in overcast conditions. I don't know that it was cooking temperatures but it was hot to the touch.

 

[XERTYX]

That's an interesting picture. I may try a small scale model like that one and see what kind of results I get. I have also considered mounting a small scrap solar panel I have onto one ran directly to a small DC computer fan (like a heatsink fan) to put inside for almost convection cooking. Although it would only work I'd imagine in a cardboard oven. Too much heat and it would surely melt.

I know PC fans can withstand a fair amount of heat. I used one in an incubator I built to help facilitate the thermostat. That was a neat project. A neighbor threw away a peltier wine fridge with the glass front door that was perfectly insulated obviously. An AC light bulb (100 watt I think) and an AC hot water heater thermostat and the PC fan and i could keep it at the almost perfect temperature indefinitely. That was a fun project. I wonder if the incubator is still in storage. That would be PERFECT now that i think of it cuz it already has a glass door and the inside is flat black.

I'm not familiar with rockwool I'll have to look into that. Thanks for that suggestion.

 

[Dingfelder]

What brand of vacuum tube cooker is it? I was loaned A GoSun for my seminar at the RTR and it was getting hot in overcast conditions. I don't know that it was cooking temperatures but it was hot to the touch.

It is a Rand solar oven off of ebay, new.  It didn't come with the reflectors I see on some videos now, though ... was just looking on youtube to try to recall the name ... GoSun looks like the same thing, but with the reflectors.  I did put a car windshield reflector underneath, and it didn't help. Maybe some really serious reflector action would help, I dunno.