How To Build Your Own Solar Oven
By Jeff Hoard, HM Ranch
One of the easiest and most productive projects I’ve built here at HM Ranch is a simple solar oven. The only expense we had was for about 10 feet of foam weather stripping. Everything else was scrounged and salvaged from things we had here in the scrap pile. The whole project started from an old 33 1/2″ x 23″ window. It is only a single pane but that just happened to be what I had, so I used it. The measurement on the oven’s pieces can easily be changed to fit whatever size window you have, but it was this window that determined the size of our oven.
The concept of this oven design is to angle the sides of the oven walls, and install a reflective material inside to bounce the sun’s rays onto the cooking vessel. We use cast iron to catch the sun’s rays and absorb the heat. And absorb the heat it does! This basically slow cooks the meal through the day the same way a slow cooker does, but using free energy from the sun instead of electricity or gas. Although the oven itself gets to only about 220°F, the cast iron Dutch oven reaches a much higher temp inside (remember, the design of this oven is to bounce the sun’s rays onto the pot). Very often I heat leftovers in our oven for lunch. We have cooked ribs, casseroles, roasts with potatoes, etc. We also hard cook eggs (up to 18 at a time). This method makes meat incredibly tender.
In the afternoons we’ll put a can of veggies in for a side dish. The cans don’t get so hot that they burst, but they do get plenty hot enough to just open and put on your plate, and you don’t have to use and wash a separate cooking pot.
Being off grid we brew coffee using a Melita drip filter so we heat a pot of water for coffee twice a day. When you add up all of the cooking gas savings I’ve just described, you can see that it is substantial. And no matter what happens in this world, if the sun is shining we’re having a hot meal!One good thing about our lifestyle is that almost every day one of us is here on the ranch and can occasionallyturn the oven to follow the sun throughout the day (the oven pivots on its post). If we are away for some reason we will put our meal in and just point the oven directly south and as soon as one of us gets home we will turn the oven west, into the afternoon sun to maximize the heat into the oven to get the dish piping hot again before we eat.
Eventually I will design and build a simple non-electric self-rotator which will make this oven much more efficient, but it is still a very handy, free energy appliance that we value and use virtually every day.
The construction of the oven was very simple compared to most of my other projects that give this much back. The pedestal was an old turnable stool. It has a good durable bearing so that is what I started with. Again, the rest of the dimensions were all dictated by the size of the window that was in my scrap yard. This was a single pane slider panel from a larger window wrapped in its own frame. The diagrams show the dimensions that I used.
The materials to construct the oven itself consisted of some pieces of 1″ x 2″, chunks of 2′ x 6″ plus some scrap 1/2” plywood with its exterior and bottom ultimately wrapped in thin aluminum flashing. This is for protection from the elements. The outside does not have to be covered, it can just be painted but being out in the elements 24/7, 365 days a year, I wanted protection that was a onetime effort and that is why I used the aluminum on the outside. And that was a good decision because it’s been outside continuously for well over 10 years now and still looks about the same as the day it was set out. I initially covered the inside with the aluminum also but better choices could have been used for the inside (something more reflective) but this is what I had here on the ranch, so that’s what I used. Even aluminum foil has more reflection than the flashing but again, durability played a big role in my decision.
The outside just wraps around into the inside. The inside pieces were custom fit and secured with small screws. I’ve since cut pieces of reflective bubble wrap and caulked those to the inside, which helped up the temperature a little. Four main pieces of 1/2″ plywood make up the body of the oven and those are shown on the diagram.
Again this was sized to work with my window and can easily be changed to fit any window size but this diagram gives a basic, proven design no matter what the ultimate size is. On the very top I made a shelf to set the pot on. I’ll twist up the top window retainer, pull the window and lean it against me, and put the pot in (or out of) the oven. Very basic, very inexpensive, very easy. On the edges where the window rests against the opening I installed a piece of aluminum channel on each side. It is not necessary but again, it was something we had in the scrap pile and by chance it fit perfectly so I used it. But again, it is not a necessity. But right there where the window sits is where the foam weather strip is installed (all four sides).
The front of the top shelf is cut at an angle so the window can tilt out and this is where I installed a small piece of aluminum angle (with one screw) as a retainer to keep the glass closed. I installed three small pieces of sheet metal at the bottom. These secure the glass but still allow for tilting outward for loading and unloading.
This design can be improved by using a double pane window to start with. Also the sides can be double layered with some foam insulation between them but again I used what we had which is quite sufficient, even in our cold valley.
This has been a satisfactorily sized oven. Occasionally, but very seldom, do we wish it was larger and generally only wish this during major holiday feasts. But again, we are very satisfied with the size of this unit.
Every day we are bombarded with natural resources. This is just one small way to take advantage of them. In one afternoon you can go a long way on building this project. Anyone with basic wood working skills would find this project very easy and certainly well worth the effort.
HM Ranch sells a DVD titled “Hoard’s Hillbilly Heaven,” a tour of HM Ranch. It is a poor man’s guide to low-cost comfortable, off-grid living, featuring an educational workshop on using the scrap pile to build inexpensive utility-generating devices. For more information visit www.hmranch-hoardmfg.com.