- Renewable & Alternative Energy
Our Solar oven – essential part of our cooking hardware
Solar ovens vs solar stoves/cookers: Overview
In How to build a solar stove I described how I built my own parabolic solar stove using two TV dishes. In this hub I will describe how I built my own solar oven. Even though both are “solar”, they are quite different as far as basic operation and functionality are concerned.
This is how solar ovens usually look like
Three or four reflecting, shining panels reflect the rays of the sun into a matt black box covered by a glass lid or double glazing of some sort. The black surface inside the box, where the cooking vessels are placed, absorbs the rays of the sun and the glass lid prevents the heat from escaping back into the atmosphere. In this way the temperature in the oven keeps on going up until it reaches 350-400 deg. F. (in ideal circumstances). The Global Sun Oven and All American Sun Oven are good examples of what are available on the market.
The is, according to claims by the manufacturer, “the world’s most widely used solar oven.” The two links at Amazon provide more than 120 reviews, with average rating of 4.4. Satisfied customers really love this unit. The All American Sun Oven (image below), on the other hand, is more than 30% cheaper, but apparently just as good. They claim that the temperature can go as high as 400 deg. F, just like the Global Sun Oven. Global Sun Oven
All American Sun Oven
Solar cookers that look like solar ovens
There’s a number of solar cooking devices out there called “solar ovens” which actually are not ovens (with a black absorbing area covered with a glass lid), but solar box stoves/cookers, since all their sides, including the area where the cooking vessel is placed, are reflective material. Only when a black, heat absorbing pot is placed where all the reflection goes, energy from the sun is absorbed and heat is accumulated in the black pot. To prevent the heat from escaping all the time and promote heat build-up, each cooking vessel is usually covered by a glass bowl. When I had one similar to the one in the picture, I used to cover the pot in a roasting bag instead, which is equally effective. An example of this type of solar stove or “oven” is the in the picture below. All Season Solar Cooker
All Season Solar Cooker
My DIY solar oven: Basic construction
My solar stove differs entirely from the ones everybody knows, as will soon be clear.
Looks could be deceiving and my DIY solar oven is a good case in point. The basic structure was made from scrap and does look a bit “scruffy”, but don’t be fooled – this solar oven of mine has never disappointed us in the more than five years we have been using it.
I got hold of a fibreglass container of 135 cm x 70 cm x 17 cm (no. 1 in image below) which forms the heart of my solar oven. On the open end this box had 2 shoulders of 1 cm wide and 2 cm high which would come in very handy to put the insulating glass panes on.
I started by cutting an opening (65 cm x 65 cm) in the top half of the bottom, where I fixed the cavity part of the oven (no. 2 in image). The sunrays are reflected into the stove by the reflecting material on the two panels on the side (no. 3 in image) and the one on top (no. 4 in image). The wheels make it possible to track the sun (east-west) and keep the panels facing the sun all the time. The panel on top is adjustable to accommodate the north-south movement of the sun as well.
My solar oven: Basic construction
Oven door of my solar oven
The oven cavity opens from behind, as can be seen in the picture below. The iron grit (no. 1 in the picture) is from mild steel and absorbs and retains the heat generated inside the stove (as does the black pot).
Oven door of my solar oven
Racks in my solar oven
My solar oven is so big, that I can put in as many pots or cooking vessels as I like; I even have the option of putting them on three racks. The structure below fits snugly into the oven and with three racks you have a lot of options.
Rack structure for my solar oven
The convection element of my solar oven
In addition to heat accumulation directly into the oven cavity by means of reflecting surfaces as described above (like all other solar ovens), my sun oven also has a convection component: The black aluminium surface (no. 1 in image below) accumulates heat from direct exposure to the sun and from reflected sunrays off the two reflecting panels on the sides. This heat is trapped beneath two 4 mm glass panes and has only one way to go – into the oven cavity through a 3 cm gap across the width of the oven cavity. This is facilitated through the gradient of the panel and also the natural process of convection (hot air moving up). As the hot air enters the oven cavity, “colder” air at the bottom of the oven is circulated down through a 4 cm gap across the width of the oven cavity into the space below the black aluminium sheet.
This heat absorbing black aluminium “element” makes a massive contribution towards heat retention in the oven cavity, since unlike reflective surfaces, it continues to gather heat from the sun even in slightly overcast conditions.
Heat absorbing black "element" of my solar oven
Using the parabolic solar stove and solar oven together
The parabolic solar stove is perfect for cooking any type of dish when time is limited. If I have only 90 minutes at my disposal, the solar dish stove is perfect; the solar oven, on the other hand, is perfect for slow cooking and for keeping food warm. Usually I set the solar oven up first to allow enough time to get the temperature up (usually 300-350 deg. F). Then I start cooking the food on the parabolic stove and move it to the oven when it’s cooked. If I prefer to cook the vegetables separately, that could be done in the parabolic stove or in the oven, depending on how I want to do it. Even when I want to do some slow cooking, I usually start with the dish in the parabolic stove and then move it to the oven where it stays for as long as needed.