Non-cooking uses of box solar cookers
Box solar cooker – An advantageous oven!
21 May 2006, Roskilde, Denmark
This article is based on my experiences and studies during my work on use and disuse of solar cookers few years ago. The work was carried out as a Ph.D. study at the Technical University of Denmark. I did my empirical work in 1997 and 1999 in Madras City but mainly in Gujarat State in India, where I visited, met, interviewed and discussed solar cooking, with about 40 urban and rural families who had a solar box cooker at their homes. Many of them did not use their solar cookers, however a small portion of them used it with enthusiasm and benefited lots of economic and other advantages. The author has discussed the problems of solar cooking technology elsewhere among others in an article: Solar Cooking Technology - How Far are Technology Promoters and Users From Each Other?
Ph.D., Master of science in technology and engineering
Hyrdehøj Bygade 261
What is non-cooking uses?
A study in Gujarat State of India among box solar cooker owners showed that a good part of the box solar cooker owners use their cookers for non-cooking purposes. By non-cooking uses I mean uses other than everyday meal cooking. Some examples of non-cooking uses are vegetable drying or baking etc. which will be discussed later. I observed that due to certain reasons, some families could not use their solar cooker for everyday meals such as lunch or dinner, but they used it mainly for non-cooking purposes. Some other families used their solar cookers for both cooking and non-cooking purposes.
The fact that a box solar cooker can be used for non-cooking purposes is a strong characteristic of solar box cookers, because in many cases the panel and parabolic solar cookers are not suitable for most of the non-cooking uses given in this article. Maybe it is specially interesting for solar cooking producers, introducers and disseminators to incorporate this aspect of box solar cookers in the introduction phase of box solar cookers.
Why it is possible to use solar box cookers for non-cooking purposes?
The thermal functioning mode of a box solar cooker is like an oven. Therefore the box solar cooker is also often correctly called as solar oven. Thermal characteristics of a solar oven is that after loading the oven with food and setting it under the sunshine the temperature rises in the box and at a time depending on sunshine conditions and thermal losses from the walls of the box, the temperature within the box stays to a relatively stable maximum temperature. Usually this max temperature is about 80-100 °C depending on sunshine, ambient temperature, quality and size of the cooker, and the type and size of the pot and the food inside. It is this range of heat maintained in an oven that makes a box solar cooker as an advantageous oven for most of the following non-cooking uses.
Some examples of non-cooking uses
In the following I will list and shortly discuss these special uses of solar cooker. No matter whether the box solar cooker is used for everyday cooking or not, it is always an advantage to use it for these special purposes. In this way the use value and profitability of a solar cooker is raised.
1: Jam making/pickle making/ketchup making
During the summer many kinds of vegetables and fruits are available at cheap prices in the market. In many places some of these vegetables and fruits are not available in the cold seasons of fall and winter. For example ketchup or chatni can be prepared from tomato in the solar cooker for consumption later in the year. Another example is to make jam or pickle out of certain fruits and/or vegetables for example mango, carrot, cauliflower etc. in the summer time for later consumption. Solar box cooker due to its proper range of temperature for simmering of vegetables and fruits can be used for preparation of jam, pickle and ketchup making.
2: Drying of vegetables and fruits:
Drying vegetables and fruits for later use (for example ginger) is another special use of a solar oven. This is desired when there is plenty of cheap vegetables or fruits available. In some food cultures people dry onion, aubergine (eggplants), ladyfingers, ginger, tomato etc. for consumption later in the year when they are scarce and also expensive.
3: Food-oil extraction from milk-cream
Box solar oven can be used for making a special food oil which is extracted from milk-cream. The procedure is that milkcream is put in a pot in the solar oven. As the temperature rises, the cream gives its fat slowly away. This fat or oil is called ghee in Gujarat. Most Indians use and love this ghee for brushing on warm chapattis (flat thin bread). The milk-cream is sensitive to high temperatures over ca. 80 °C. Therefore attention is required not to allow the oven to be overheated. How to lower the temperature of a solar oven is discussed at the end in the article.
4: Heating milk:
A box solar cooker is ideal for heating milk for drinking, cream making or other purposes, because the temperature range a solar cooker reaches will not burn the milk. Milk is sensitive to temperature over ca. 96 °C, it will simply burn and stick and an unpleasant odor will remain in the boiled milk. Here again the temperature range of the solar oven is the advantage.
5: Baking cake and bread:
Baking bread, cake and the like can also be carried out in a solar box cooker. Here the appropriate temperature range of the solar cooker is decisive not to burn the cake but to bake it just as an electric oven does it in a modern kitchen.
6: Insect killing of grains:
In some areas and in some seasons, the grain storage of the family may be exposed to development of small insects in the grain. These insects might be mixed with grain! Getting these insects away from the grain may usually be a difficult task to be done manually. In Gujarat I saw that some families put their insect-exposed grain, bean, peas etc. in the solar cooker a few hours during a day or two, in this way the insects are killed due the heat of the oven while the grain, beans, peas etc. was not damaged. Afterwards the family could easily get rid of the dead insects by blowing them or using sieve.
7: Another non-cooking use of box solar cookers is to pasteurize contaminated water. This advantageous use of solar box cooker has been introduced by Dr. Robert Metcalf. The interested reader is suggested to consult writings by Dr. Robert Metcalf which is also available on the website solarcooking.org.
During the study in Gujarat I observed that some families decreased the temperature and moisture developed in their solar cookers, by slightly opening the top glass lid of their cooker by temporarily creating a gap for the oven. This is indeed an easy and effective way to control the temperature/moisture within the oven. One can for example place a coin or a small glass ball to keep the top sash open. This is necessary specially when the sun is high and one should avoid high temperatures for some of the above-mentioned special uses for example when one is heating milk.
Published: May 21, 2006