Economic viability in the use of solar collector in productive agricultural chains
Clean Technology 2008

Economic viability in the use of solar collector in productive agricultural chains

J. Bione, P.B. Carvalho, R.B. Fellows
Companhia Hidroelétrica do São Francisco - CHESF, BR

collector, solar energy

Since the XX century, the world has suffered through exploitation of its natural resources, atmospheric pollution and soil degradation. In the wake of this ecological question, the so called alternative sources of energy are gaining more and more space. These alternative sources, besides not damaging nature, are renewable, and therefore perennial. Examples of renewable sources include solar energy (water wheels, aquatic turbines) and biomass (material of vegetal original). The Brazil has a remarkable vocation for generation of energy by renewable sources. The rural medium, especially, can easily be totally or partially supplied by using alternative forms of energy production. The climate condition and relief are favorable in the country, principally for solar energy, because it presents an abundant amount of sun during almost all the year. There are two ways of using solar energy: active and passive. The active method is based on transforming solar rays into other forms of energy (thermal or electric) while the passive is used form heating buildings or apartment blocks. This work, studies the economic viability of the use of solar collectors in productive agricultural chains, therefore, a description of their domain and application and principles of functioning of solar panels and attention to installation and maintenance is to be carried out. There areas under focus in this study are firstly the drying of foodstuff, for being a compact technology, being able to be operated by the agriculturist, another action is the obtaining of more elevated temperatures around 100 C, for application in washing and decontamination of productive lines, and lastly for use in solar refrigeration processes, which is an obvious application of solar energy, because the periods it is most necessary coincide with periods that have more solar radiation, as for example, the refrigeration of products that have been harvested and are waiting to be transported, because this is still presented as being little used although it has an enormous future potential. In the initial study, it was verified that the investment is relatively high for obtaining water at 70 C, but the time of return is normally 2 years. The cost of a basic system for a 2 m2 collector and 200 liters reservoir are around 700 dollars. Most of the cases were analyzed using the water transference fluid. In some systems the water is made to circulate between the collector and the deposit/accumulator by means of a pump, in others the circulation is impelled by the thermosyphon effect. In the systems with termosyphon the heated water in the panels expands and rises up to the accumulator that is installed above, thus the water is replaced when used. They are cheaper systems because a pump is not used, not even a controller, just that it is obligatory that the accumulator to be placed in a more elevated position. The thermosyphon systems are used in zones that have a warmer climate while pumps are used in other places. The characteristic curves of the analyzed systems were researched. The temperature to be obtained in the collectors basically depends on correct alignment, the degree of finish to be given to the material that composes the reflector surface and the respective concentration factor. In a general way the temperatures obtained using parabolic concentrators are between 100 C and 393 C for concentration factors varying between 2.5 and 24, approximately where the maximum value refers to a reflective surface formed by flat mirror segments. In the case of using commercial aluminum that is manually polished, the maximum temperatures obtained between 10 and 12 o’clock in the morning with radiation varying from 1 to 1.2 kW/m2, reaches 250 C. It was verified that economic viability using collectors in productive chains, depends on the type of application and the agricultural product to be dealt with.