Effective utilization of solar energy in agriculture
Effective utilization of solar energy in agriculture
（農業における太陽エネルギの有効利用）
Ibrahim E. A. Elbatawi
Effective utilization of natural energy in agriculture has been done in many countries all over the world. Although Japan has not enough fossil energy resources, the nature provides a variety of natural energy such as solar energy.
The objective of this study is to collect the solar energy incident at day time and use it for many proposes in agriculture such as:
１) compare the energy utilized in Egypt with that collected in Japan.
２) heating inside a greenhouse to promote the vegetable germination.
３) heating the brine inside a solar still to enhance the fresh water productivity and use it for seedling irrigation inside a greenhouse.
Solar energy collected and predicted in Okayama, Giza and Kafr-Elsheikh
Data collected in Okayama city (Japan) was compared with that collected in Egypt (Giza and Kafr-Elsheikh). The comparison of the proposed simulation method with the measured data showed a good agreement between two different cities in Japan and Egypt. Moreover, in order to update the measurement data, it is also possible to include the local climate changes. As presented here, the result of the proposed simulation method belongs to the class of random processes, and in this sense is an extension of the means which have been applied so far to energy calculations for Giza and Okayama.
During January, in Okayama the average ambient temperature, maximum water temperature inside the storage tank and collected energy were lower than in Giza. On the other hand, during July for example, the average ambient temperature, maximum water temperature inside the storage tank and collected energy in Giza were more than that collected in Okayama. The reason was the different of latitude in both cities, therefore, the daylight in Giza was longer than the daylight in Okayama.
We can see also that in this worst solar month in January the solar water heater still provides 35.25% of the energy for Okayama and 40.37% for Giza. That was because in Okayama the number of clear days were 6 days only but there were 19 days in Giza.
Promotion of germination by heating greenhouse using solar energy
Solar system including a solar collector was prepared to collect the energy all the time and store it inside a storage tank. Two greenhouses was constructed to promote the germination of vegetable seeds. Solar collector efficiency was almost 50%. The later was taken as solar system efficiency. It was shown that the germination of vegetable seeds was very sensitive to the surrounding temperatures. If solar energy is collected and stored by the solar system, it can be used for various purposes in the agriculture.
We found on effective utilization of solar heat energy for heating a greenhouse to germinate vegetable seedlings.
During heating at night inside the greenhouse, it was difficult to know exactly when the lowest temperature well take place. Using the measured temperatures from the preceding days and considering the minimum and maximum temperatures given by the weather forecast at Okayama city, it was possible to compute accurately temperature for the next day.
It was also clear that, temperature at any time is not related only with the temperature of previous time as mentioned by Troeger and Butler but also with maximum and minimum temperatures for the next day.
Production of fresh water by solar still
Numerous performance correlation have been determined for a solar still with preheating but solar still productivity less than required
A schematic diagram of the solar still and its dimensions was constructed at Okayama University laboratory. It should be noted that, rate of dust and dirt covering on the external side of the glazing will increase as the slope decreases and the rate and extent of natural cleaning by wind and rain will decrease. The results concluded that solar still productivity increased with the greater temperature gradient due to increasing of solar radiation with air velocity blown on the outer surface of the glass cover. Increasing the air velocity the productivity increased
The use of preheating was greatly enhance productivity especially at night. The solar still productivity increased about 4.3 L/m2 per day by increasing the temperature gradient to 16.8 ℃.
The performance of the solar still can be measured by its efficiency. In this study, the overall efficiency was 32%. The daily solar still production was clearly affected by solar radiation, ambient air temperature, air velocity by fan and temperature differences between basin water and glass cover.