Who knew cooking with energy from the sun would be so difficult?
Cooking with rays from the sun- what could be more delightful, or more efficient? The same rays that warm the skin can heat food as well- one merely needs to concentrate the heat a few fold. Well, doing so is remarkably difficult to do in practical terms. Not only do you need to concentrate the sun's heat, but then you have to preserve the heat you collect, without blocking out the light with all that insulation. This can be quite a trick. Thermostatic control? You must be joking- none of the currently sold or proffered DIY projects incorporate such an extravangance. The current state of play is a slightly demented world of youtube videos, fly-by-night companies, and charitable efforts pointed at developing regions. But rest assured, it can be done.
Naturally, the most significant drawback is that the sun doesn't shine all the time, confining solar cooking to mid-day times, and sunny conditions. Several kinds of cookers have been developed, each with individual drawbacks and features.
- Parabolic stove
- Vacuum tube oven
- Closed box oven
- Open panel oven
First off, the parabolic solution puts the premium on power. While the other cookers are akin to ovens, this one is more like a range / stove. It gets extremely hot and cooks in a hurry. The concentrated light from the sun needs, however, to be constantly tracked and aimed at the pan on the burner. Yet it is an invisible flame, presenting some difficulty. It can burn a finger or blind you in an instant. One company developed a reasonably practical design, complete with glowing video. But then it promptly shut down and disappeared, I assume due to the daunting legal liability implied in selling such an appliance. These cookers remain very much a DIY, and at your own risk, proposition.
 |
| A parabolic cooker- adjust often, and use with care! |
Second are vacuum tube ovens, which are basically thermos bottles with sun-facing inputs. These have outstanding insulation, so they capture the radiation coming in very effectively, storing it as heat. They can be used in cloudy conditions and maybe in non-mid-day conditions. The downside is that the thermos structure limits capacity for food, and also hides it from view. These also come in water-heating versions, filling a core camping and emergency need.
 |
| A vacuum tube style of oven. This one has quite high capacity. The central thermos provides extremely effective insulation, collecting every bit of the insolation. |
Third are closed-box ovens, which are perhaps the most widely used form of solar cooking. Given enough insulation and a well-sealed glass top, you can make a reasonably practical oven out of cardboard boxes, wood, or metal, which get up to 350 degrees °F. This is a slow kind of cooker, perhaps more like a crockpot than an oven, taking quite a bit of time to heat up. They are not so sensitive to light direction, so can be left out for lazy afternoon and will still work. This is an amazingly active area of DIY activity, with endless variations. One of the most impressive I have seen is a sleek, low oven build of glass and wood, meant to stay outside full time.
 |
| A commercially made box oven, with glass top and room for one or two pots. |
 |
| A DIY version of a box oven, with clean lines and very high capacity. |
Lastly, a more portable version of a solar oven is an open panel oven, where a set of foldable or collapsable reflective panels surround the pot, without much other structure. These are maximally simple, and aimed at camping and other portable needs. But they need something extra to hold in the heat around the pot, which may be a plastic oven bag, or a pair of glass bowls that go around the black pot inside. When properly protected, set up, and with large enough collectors, these can get to 300 degrees and work well cooking stews, rice, etc. These enjoy a wide variety of DIY efforts and styles as well, and one of the best is offered by a maker in Southern California.
 |
| A panel cooker being used on the go. Note the glass bowl holding the central pot. |
Those are the current types, each with its pluses and minuses. Once one considers solar cooking, it is natural to want to deploy it to those who really need it- the rural and poor around the world, who have lots of sun, and not many other resources. The scourge of traditional cooking fuels in these areas is particularly alarming, usually being wood, coal, or dung, which lead to deforestation, climate change, land depletion, and copious pollution, both indoor and outdoor. Thus solar cooking becomes another sort of colonial dream foisted on the less fortunate, who have not set up proper infrastructure to pillage the earth and pollute the atmosphere. But the various impracticalities of solar cooking, including inconvenient timing, outdoor location, low capacity, slow speed, unusual, non-local, and fragile materials, have doomed such efforts to marginal effectiveness. Maybe some further leap in the technology, like incorporating a heat storage mechanism (rocks?) might solve some of these problems. It is amazing, really, how convenient the stored /reduced forms of carbon (in biomass and fossil fuels) are for our needs, and how hard they are to replace.
