Evaluation of solar energy on the roofs of livestock houses
AbstractThere is a great potential for production of thermal and electrical energy by means of solar collectors on farms. To assess in advance the performance of the alternative plant solutions, a computational model for the determination of solar energy absorbed by surfaces with different exposures as a function of latitude, day, orientation and inclination has been created. Its application to roofs of buildings typically used for animal housing is presented; these were mono-pitch, gabled, and shed type roofs. For each building, the annual energy absorption per unit of floor area is calculated by varying orientation and slope of the pitches. For roof surfaces exposed only in one direction (mono-pitch or shed), the orientation is shown to be a dominant factor with respect to the slope in determining the annual energy uptake. The maximum uptake is obtained with exposure to the south and is greater the higher the slope (up to 67.5%). For gabled roofs, the total uptake is negatively affected by the worse exposed pitch and does not vary significantly, for a given slope, with orientation (up to 2.8%). The maximum gain is obtained with the optimal building azimuth (0°) and the highest slope. The shed type, since it is affected by the shade induced by the upper pitch over the lower, cannot reach the level of a mono-pitch roof: -1.5% with a slope of 10% and -21% with a slope of 67.5% with the optimal building azimuth of 90°. However, its performance is slightly higher than the corresponding gabled roof (+2.5%), therefore, it could be a convenient alternative if optimally oriented and, above all, if the collectors are installed on the predominantly sunny part of the roof.
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Copyright (c) 2013 Paolo Liberati, Paolo Zappavigna
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