4.1. Education. The concepts (sustainability and renewable energies) were learnt easily. Sometimes it was extremely difficult to keep the students focused. I cope with that giving more practical examples, inventing some game, etc. The audiovisual material (videos and pictures) turned out to be of extreme importance, because they could visualize examples.
Knowing until which extent they will use this knowledge in the future is at this point impossible. I tried to point many times that they have a huge responsibility, considering the fact that they live in a unique ecosystem of which they are responsible. Nevertheless the word ‘unique’ is not easily memorized if someone think it is ‘granted’.
4.2. Solar energy. Teaching how a solar panel, oven or heater works was successful. The solar radiation of São Tomé is powerful, especially in the rainy season, but also in the dry one called gravana. Due to the proximity of the area to the equator, the orientation of the day-trajectory of the sun is constant all year long. The main problem was that the radiation is scattered, as the weather is constantly alternating between sunny and cloudy. As a result we decided to use the solar panels and oven for preparing thinks that required long times of cooking (jams, biscuits, soups… ) or for frying when the radiation is strong (eggs or ‘fruta paõ’).
4.2.1. Solar panel 1. The system was proved to be easy to assemble and the major benefit was that soon we were able to collect information in regard to solar panels. However, the panel was not able to boil water in any of the circumstances that we tested it. The maximum temperature reached by 1 L of water was about 70°C.
It is of a severe importance that the cardboard is flat and dry from the beginning and maintained likewise during the working-life of the panel. Special care must me taking when gluing the aluminium foil to make it flat; it is recommended to cut it in small pieces (10x10 cm).
4.2.2. Solar panel 2. In São Tomé is almost impossible to find aluminium panels in the shops, and shipping would last too long. As a solution we first used aluminium foil and then we asked in the local printing house, in where the aluminium panels are used in the manufacture of the newspapers. The waste panels have one side reflective (still useful after cleaning with gasoline or organic solvent) and they are free of charge.
In the first attempt we used aluminium foil, in which case the same recommendations that for the solar panel 1 are given. Using foil resulted in heating 1 L of water up to 80-90°C in the sunniest days, enabling cooking eggs for example.
In the second attempt we used aluminium panels (as it has been described in the ‘workshops’ section), enhancing significantly the heating capacity of the unit, thus boiling water and frying was possible in about 20-30 min of exposure.
4.2.3. Solar oven. The unit was a success from the very beginning, enabling reaching temperatures above 120°C within 30 min of exposure. The most important parameter is insulation; special care must be taking avoiding holes. Although the easiest design looks like a box we recommend the use of reflectors close to the glass, as the radiation greatly increases.
4.2.4. Solar water-heater. Depending on the copper tube it must be required to have material to twist and turn tubing. The same requirements of insulation (as the solar oven) are required for the heating element. During the start-up of the unit care must be taken filling the heating element with water, avoiding the presence of bubbles of gas into it.
The unit was able to heat 40 L of water up to 30°C in about 3 h of exposure.
4.3. Biogas. The tropical conditions of São Tomé made this land very attractive for developing biogas technologies. However the number of kettle in the country is relatively small so incrementing this number or exploring the digestion of other renewable sources can lead to a sustainable energy for the country.
4.3.1. Pilot-plant digester. The unit was able to build up pressure; however the resulted gas was not flammable (probably because of the burner). In this sense the system was a failure. Originally we built an additional system based on hydraulics in order to collect the gas, however as the number of connections (shielded with silicone) increased, so it did the chances of leakage. Minimizing these connections is therefore recommended.
4.3.2. Kitchen-plant digester. If tubular plastic is difficult to acquire, as in this case, new approaches are needed. In the literature it is advised to use a length:diameter ratio of 7 for the digester. As the only tubular plastic available had 1.9 m of diameter we rolled one side with a hose, fixing it with a rail on one side of the digester, resulting in a tube of 1.5 m of diameter.
The final volume of the digester was 5 m³.
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