CERC Green Solar Oven

A solar oven is a great way to conserve resources and tap into the wealth of energy that hits the Earth every day.  In this Instructable, we will show you how to construct a high efficiency solar oven out of mostly waste or scrap parts you probably have lying around your house.  The intention here is to use these materials that would normally take up space in landfills for harnessing the power of the sun.  In this way, we are not only re-purposing and reducing waste, we are conserving resources. 
Many people believe that these ovens are novelties and can not be used for anything.  The truth is this oven heats up very fast and care should be taken when handing it or any contents when at operating temperature.  Under spring weather conditions and when pointed properly at the sun on a clear day, it will pass 150°C (300°F) within 10 minutes. 

Step 1: Supplies and Materials

For this project you will need to find:

Several Different Sized Boxes (some very large ones are useful)
Clear Packing Tape
Styrofoam Packing Peanuts or Shredded Paper
Razor blade
Black Spray Paint (enamel) or Black Enamel Paint in a can (you should not use latex paint)
Scissors
Paper Clips
Aluminum Foil (heavier and shinier the better)
A piece of Glass or Acrylic
Glass cutter (if glass is used), a Saw (if acrylic is used)
Rubber Bands
Can to cook food in
Short pencils or dowels which no longer have a use
A ruler (yard or meter stick would be best)
Pen or Pencils
Calculator


Optional:
Thermometer Probe to monitor temperature

Comments

[Chrystalkay]

Question... Wouldn't a glas topped pyrex type baking pot be an acceptable heat absorber? Does the whole top have to be glass? Or would there have to be extended reflector material around the inside of the box too to make something like this work?
Or wouldn't a black ceramic lidded cooking pot work inside the chamber without the glass lid?
I am thinking of camping and such where you wouldn't want to cary the glass around, as well as weekend yard cooking.

[SolarPoweredGardener]

I made an open type cooker to see if they worked, the type you put the pot in an oven bag... It worked well.... The bags kepy breahing though so what I found was big plastic domes... You can get them in gardening shops... Thay are cloches used to cover young plants to protect them from the frost... They work great and it's easier to remove of you need to stir whats cooking...
I'm now building a big box type with sun tracker... Am doing a instructable for it so keep your eyes open... Should have it finished by xmas 2010....

[hyperfocused72]

You can not use styrofoam for insulation because they give off toxic fumes when heated. Read the introductory manual at www.solarcooking.org for safer alternatives.

[flio191]

To add to the efficiency of the heating, it would be cool too see an insulated window used in place of the glass, as air, or a vaccum would be the best insulator for convection heat.

[3point2]

Yes, double glazing would be more efficient.  Keep in mind, though, that the additional panes of glazing due cause losses of their own so you have to weigh your options.  An evacuated (vacuum) glazing is the most ideal since there is absolutely no convective losses.  That said, this was supposed to be a project anyone could do using stuff they found around the house that would end up in the trash.  It is very unlikely someone has the setup required to create an evacuated double pane glazing for their oven.  ... although... that does sound pretty cool now that I say it!  8^)

[Sarah Stephens]

I've heard of making a solar oven before using transparent oven bags in place of glass.  Can anyone tell me if this is a good idea?

[gaiatechnician]

Why not a thin black piece of metal  in a hollow under the oven and reflect the light to it?
That way, no glass at all!  You might get less energy in because it is all reflected and none direct but  you could have the top super well insulated and there would be much less convection losses from under the oven.
A guy called David Delaney thought of that years ago but I do not think he ever tried it.

[3point2]

Yeah, this larger black absorber box underneath might work but would probably cause extreme losses in heat.  Consider this, there is a very good reason your oven (or even toaster oven for that matter) has a door.  It's not that you couldn't heat the food without it but you would loose most of the heat through convection.  Actually, very little light is reflected off the surface of the glass if the recommended angles are observed.  Given the Fresnel equations I solved for, the losses are only about 8% in the worst case.  A way better scenario than the losses due to an open air cooker. 

[sclausson]

When I made solar box ovens I used the large oven bags in place of the glass. To hold the bag, cut down both sides and open up. I made a frame from a screen repair kit. It sounds like a drum when you thump it. When bag wears out simply remove and put a new one in. Make a foil hinge to hold it.

[CapnChkn]

Excellent Instructable, just one caveat.

The glass used should be TEMPERED GLASS.  I know that will make it hard to cut, but I built one of these using quarter inch (6 mm) plate I picked up somewhere.  After adding the reflectors, I saw using an oven thermometer, the temperature had reached 350 degrees F (175 C), grabbing my camera, I leaned over to take a picture, letting my shadow fall across the glass.  When I leaned away again I heard a "CLINK!?!"

Looking back, the glass had broken.  It didn't shatter, it cracked in a wavy pattern from one side of the glass to the other, perpendicular to the surface of the glass.  Though that sounds anti-climactic, the edges were still "sharp as glass."

[sdallesasse]

I would think that laminated glass or wire reinforced glass would be the two best choices considering this information.  They allow the least fragmentation to be released.

[johnny3h]

I do hate to have to inject a negative here, BUT... thermal imbalances on Tempered glasss WILL also cause shattering.  The only difference being that instead of a single crack as described, the Tempered glass will have thousands of smaller cracks following the crystal pattern in the temper.

For years, all across Texas, tempered automobile back glass windows have shattered during the summer months due to being parked in the hot sun with all the other windows closed.  It has happend to me once, and I have known several people over the years who have experienced the same problem. 

Therefore, Tempered glass is no improvement, AND you CANNOT CUT Tempered glass AFTER it has been tempered.  It HAS to be cut/shaped, and edges finished BEFORE TEMPERING.  I got this info from a Tempered glass fabricating company years ago.

[redplanet]

Tempered glass cannot be cut. I speak as a former professional glazier. Any attempt to cut tempered glass will shatter it into tiny crumbles.

However, if you have a piece of tempered glass to recycle, e.g. from a refrigerator shelf or whatever, you could design the oven around it.

[johnny3h]

In addition to redplanet's point, what difference does it make IF one's glass is not one piece??

IF the edges of one's multiple glass panels are properly fitted, the millimeter, or so, air gap will not be significant in the escape of either heated air, OR reflected infrared energy.

So, to make a larger opening, use multiple pieces of Tempered glass windows from whatever source.

[gaiatechnician]

There is a guy on youtube who made his oven from scraps from construction sites.  He just uses 2 pieces of glass, he has them loosekly put in  and accepts the little loss between them.  I think this cracking (which is a big feature of amateur build solar ovens) is mostly because people have the glass in tight. The expansion widthways and lengthways (with no room to move)  when it heats up and cools down is what is causing so many breaks.
So just like concrete roads need expansion joints, it seems that glass needs them too in solar ovens.

[scraptopower]

Could you use the glass from an old microwave or oven ? That would be easy to get hold of and temperature resistant ?

[3point2]

Good Point.  I wrote this with a broad audience in mind so I was hoping anyone much under 18 would choose acrylic with the risk of it sagging under the high temperature that can be reached.  Indeed, the sudden heat change from a cloud can cause the temperature to drop and thus risk cracking the glass.  One possible option is to place several black or black painted stones inside to act as heat reservoirs.  Not only will this keep the temperature more steady but will hopefully put less stress on the glazing.  The downside is that it will not heat up nearly as fast from a cold start. 

[pattyaitch]

I love it.
My first solar oven was one we made from a foam cooler box. We cut the front 33°, as that seemed to be the best angle for the sun in S.Cal. The glass we had cut from double strength~~never even thought of tempered way back then. It was lined with foil, with a black cloth on the bottom (over the foil) and the reflector was made of three asphalt floor tiles covered  in foil. Favorite thing to cook was Jalapeno/cheese strata.

[Sonoffar]

A very good instruct-able. I think even I could follow your guide and end up with a functioning solar cooker. I assume this was a student design assignment and I am curious if any one has done a cradle to grave cost assessment on this sort of "resource friendly" item. By that I mean:  What does it cost to produce and or manufacture all of the components utilized? Which components could be reused or recycled? Which components would be 'trashed'? And of course is there any cost or environmental savings achieved with this sort of project?

[lieuwe]

 awesomecakes, about the flaps needing to be 35 degrees tough, that's only valid if your flaps are as long as your glass, the angle is approximately 26.4735*tanh(2.33776*x) with x being the glass-to-flap ratio, eg if your glass is 13 cm and your flaps are 26cm, x is 0.5, which would result in an angle of 22 degrees. but don't rely on this heavily, i could have made a huge mistake somewhere in that formula. anyhow, nice ' ible, just built my own, gotta test it tomorrow tho, it's already dark here(and it's cloudy)...

[lieuwe]

 that formula is too inaccurate, i made a huge mistake, making a new formula, should be done in a couple of hours 

[3point2]

Though I don't think I mentioned it, the simple multiplication guide to get the ideal angle takes into consideration the refractive index of the glazing.  If the light comes in at a super low angle, it will be almost totally reflected due to the higher refractive index of the glazing.  (At low angles, windows can act like mirrors.)  While those are not the idea numbers, they are very close.  If someone was looking to improve dramatically, they could use real scrap or broken mirrors as the reflectors and that would probably give good performance enhancement. 

[lieuwe]

 making it round ought to help some too, now the sun hitting the edges off the reflectors needs to be reflected twice, but it works pretty good already

[peaceamidst]

    Nice, reminds me of when me and my brother used to make small tin foil ovens. We didn't make a hole in the top or anything though. We would just put like a piece of bread in it and set it outside. But we used to make little drawers and stuff. It was funny.

[kelseymh]

Extremely well written!  There are a few typos ("Lets" instead of "Let's"), but nothing substantial.  Good explanations of the "why" behind the design, as well as practical construction details.

Rated and featured.

[Kiteman]

(I don't see any check-marks in the feature settings?)

[kelseymh]

What?  You're right.  Let me try again...

[Kiteman]

I see them now.