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Boiling, Cooking, Baking

First published May-2010
last update 27-July-2010

Though roasting and charcoal seem like applications particularly easy to spread on a global scale, as discussed in the previous chapter, there are of course other simple activities that are easily developed, but may have one or two barriers to overcome before spreading world wide. However, once solar concentrators are fairly common for things like roasting and charcoal, then these other activities will follow as a matter of course. The more development and examples exist in the mean time the faster this process will go.

Boiling water

Boiling water takes a surprising amount of energy, and is essential in nearly all people’s quotidian lives. Boiling water with a solar concentrator is particularly easy to put into practice as only a pot is required as an application.

The only barrier is that there are few economic activities that require only boiling, and the one’s that do generally depend on the time of day or in an urban environment where space is a problem.

What’s more, a high powered solar concentrator built for any other application can boil water in extra sun hours. Especially in a decentralized system, there are few applications, if any, that must run all the time. So, with the installation of any high power solar concentrator for any of the reasons any extra sun hours can be used to boil water at little extra cost.

Another advantage of boiling water with a high powered concentrator is that it boils quickly and so there is little waiting time.

Solar concentrators would also be an immense health revolution in regions where many people cannot afford the means to sterilize drinking water. When boiling water for sterilization is the only activity even simple methods such as placing the boiled pot in a larger pot to pre-heat the next water to be boiled, can speed up the process.

Cooking and Heating

Cooking is the local solar application that has so far been the most developed.

Collective cooking has existed for some time, notably in India. Very numerous solar cooking programs exist all around the world developing a wide range of solar concentrators (see

Cooking requires relatively low temperatures. The challenge is that cooking is very sensitive to cultural habits, the time of day, and in urban environments space can be a problem. As solar cookers generally need to be used outside, this presents a practical problem for women. Though cultural habits can be changed to some degree, practical solutions must also be sought, such as placing the focal point in the house, through a whole in the wall. Though an in house focal is not a complicated idea, it requires a radical change in architecture for most houses on the planet.

So, for solar cooking to become a new cultural norm may require as much an architectural change, to integrate solar cooking into the home, as it does a mastery of solar concentration.

This architectural change is also necessary for heating homes passively with solar, using windows and intelligent design. So we can conceive of both these challenges together as a fundamentally architectural problem.

Changing both existing buildings and architectural practices is extremely difficult, so the more commercial applications that are easy to implement are developed the more it will become obvious that solar energy can power the majority of humanity’s energy needs and the solar way of thinking will instil throughout society. Though, as with every example, the more experience gained in solar cooking and passive solar architecture the sooner and faster the explosion of solar cookers and architecture will be.


Unlike roasting and charcoal, baking food is more sensitive to the time of day. For any commercial baking it is not possible to simply wait for there to be good sun to bake, so a hybrid system with wood, bio-char, gas or electricity should be envisioned. Furthermore, by increasing the mass in the oven, more thermal momentum can be accumulated resulting in more even baking and greater stability of the oven temperature from passing clouds.

However, not only food can be baked in the solar oven. As seen in the previous chapter, a char box can be easily created to either simply dry the wood or turn it to bio-char. So, an oven originally installed to make charcoal can slowly be used to bake in extra sun hours, as the users realize baking directly with the sun means less work to make charcoal, or more charcoal can be saved to trade.

Lime Mortar

Traditional lime mortar requires only baking at 250 °C for a around 5 hours. Lime mortar is more flexible than concrete and can breath. Flexibility allows for walls to move without cracking and breathability allows moisture to be expelled rather than to condense. What’s more, when lime mortar is stressed to the point of cracking it tends to make many small cracks rather one large one; these smaller cracks can self heal when atmosphere enters in and causes further carbonization of the mortar.

Lime mortar, and other traditional mortars, can be easily made in a basic solar oven.

Plaster cannot be made without high temperature but can be recycled by baking at relatively low temperature (all the moisture will be expelled and the hard plaster will return to powder). With much higher temperatures plaster and concrete can be made.

Though baking bricks requires much higher temperature, we should note that adobe construction and compressed clay bricks require no baking. Though not a mechanically strong as other materials, such clay constructions are flexible and breatheable, self regulating a comfortable atmosphere.

Written by Eerik Wissenz.

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