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HIGHER PERFORMANCE SOLAR CROP DRYER KIT FOR DEVELOPING ECONOMIES
Impact/Purpose:
Solutions to hunger and farming problems have been sought throughout the world but especially in developing nations. After battling growing issues, the final obstacle is crop drying. The drying of harvested crops is necessary so that the crop may be processed, stored, and delivered to the consumer with a minimal amount of loss due to spoilage or insect attack. In the best case, fossil fuels are used with drying systems. But for farmers in developing countries, extremely low income cannot overcome increasing fuel and energy prices; furthermore, in many areas electricity and fossil fuels are not available at any price. Thus, a large segment of the world’s population relies on simply setting the crop out in the sun. However, such non-concentrated solar energy may not be sufficient to adequately dry the entire crop. Further, this also results in long drying times where the crop, laid on mats, trays, or the ground, is exposed to bacteria, bird and insect attack, dust, wind dispersion, and other environmental factors. Any innovation to reduce drying times will speed the time to storage and thus protect the crop.
It is proposed to design, build, and test a novel solar crop drying system based on the compound parabolic concentrator (CPC) concept. It is an improvement over open-ground drying by providing crop protection and concentrated sunlight to speed the drying process by a factor of at least 3. The ultimate goal is to design towards a kit form so that this system can be easily distributed throughout the world.
This project enhances P3 sustainability by offering an improved methodology for drying crops. This novel, proposed solar system takes advantage of a blackened surface to improve solar radiation collection at the crop; a covering film to reduce thermal losses as well as minimize bird and insect attack, dust, and wind dispersion; and concentrating limbs to increase collector efficiency, temperature, and decrease dr
Solutions to hunger and farming problems have been sought throughout the world but especially in developing nations. After battling growing issues, the final obstacle is crop drying. The drying of harvested crops is necessary so that the crop may be processed, stored, and delivered to the consumer with a minimal amount of loss due to spoilage or insect attack. In the best case, fossil fuels are used with drying systems. But for farmers in developing countries, extremely low income cannot overcome increasing fuel and energy prices; furthermore, in many areas electricity and fossil fuels are not available at any price. Thus, a large segment of the world’s population relies on simply setting the crop out in the sun. However, such non-concentrated solar energy may not be sufficient to adequately dry the entire crop. Further, this also results in long drying times where the crop, laid on mats, trays, or the ground, is exposed to bacteria, bird and insect attack, dust, wind dispersion, and other environmental factors. Any innovation to reduce drying times will speed the time to storage and thus protect the crop.
It is proposed to design, build, and test a novel solar crop drying system based on the compound parabolic concentrator (CPC) concept. It is an improvement over open-ground drying by providing crop protection and concentrated sunlight to speed the drying process by a factor of at least 3. The ultimate goal is to design towards a kit form so that this system can be easily distributed throughout the world.
This project enhances P3 sustainability by offering an improved methodology for drying crops. This novel, proposed solar system takes advantage of a blackened surface to improve solar radiation collection at the crop; a covering film to reduce thermal losses as well as minimize bird and insect attack, dust, and wind dispersion; and concentrating limbs to increase collector efficiency, temperature, and decrease d
Description:
The initial design was drawn up as a preliminary draft using Pro-Engineer software. A 4X optical CPC concentration ratio was chosen, then truncated to 3X. With a receiver (crop) width of 0.5 m, the CPC aperture width is 1.5 m. This design was used as a basis for purchasing materials and hardware before actual fabrication of the CPC was undertaken. Chosen were materials that were readily available because the Phase I objective was to obtain some preliminary data showing whether or not the concept is feasible.
The first portions of the crop dryer were the supportive struts designed to hold the mirrored limbs in place above the crop trays and to elevate the trays above the ground for easy accessibility. The limbs for the reflecting surface need to conform closely to the required curvature to maintain collector efficiency. Because of this, the calculated curvature was cut on a polycarbonate plastic stencil using a computer-controlled laser at Northern Illinois University.
The struts, from 4’ by 8’ sheets of medium density fiberboard, were cut with a scroll saw and then all six were stacked for sanding. Sanding the edges not only gave the surfaces a smooth finish but it also ensured that the parts were identical. The struts were assembled into sidewalls for the collector with 16 bolts per strut and two support plates which are 14 gage sheet metal and cut by computer-controlled water jet. Lastly, the six strut halves were assembled using forty-eight 0.375’’ x 1.25’’ bolts and hex nuts as well as 96 flat washers and 48 lock washers. Figure 2 is a photograph showing the struts, braces, and cross-members holding the CPC halves together.
Figure 2. Photographic View of CPC Support Structure
Cross-members were further reinforced with wooden boards cut to approximately 8’ long with three notches each; the notches were 2” deep and spaced 3.3’ apart. Notches were cut into the struts so that the cross-members would fit into the struts. Additional cross-members ran between strut pairs and were screwed using 1.5’’ long wood screws. The base stand is 4’ by 8’ medium density fiberboard and elevated off the ground by 2” by 4” boards which also allowed for tilt motion to the entire facility. To tilt the crop dryer, eight hooks (four on the stand and four on the cross-members) were affixed and linked by an adjustable length of rope.
Two trays were designed for the bottom of the CPC; they are plywood and lined with black, waterproof plastic. The rectangular trays measure 1.0 meters by 0.5 meters by 76.2 mm deep and can hold approximately 20 kg of wet grain. To provide a track guide for the trays, angle iron, 2 meters long, was screwed and glued to the struts. Finally, the sidewalls, with the exact CPC shape, were fabricated from two pieces of smooth panel board measuring 2 m by 1.44 m and 2 mm thick. The flexible sidewall was easily snapped into the struts, then glued and screwed into place. A mirrored film will be attached to the sidewall contours and a transparent plastic plate will seal the top of the CPC to complete the solar system. Figure 3 displays the CPC structure with sidewalls, without mirrored surface, and crop trays.
The effects of air ventilation will also be tested using an array of ten small brushless DC fans powered by a 12 VDC, 1 amp, photovoltaic solar cell. A battery is used as a buffer between the solar cell and the fans to protect the fans from over-voltage and to maintain power during cloud cover. Figure 4 illustrates the fan array. Each fan has an average air flow rate of 35 cfm for a total of 350 cfm. A control box has the ability to power the fans individually to vary air cfm. The fans are mounted in a sheet of clear acrylic plastic cut by a water jet.
Figure 3. Photographic View of CPC Support Structure with Crop Trays
Figure 4. Schematic of CPC System with Fan Array