FIGURE 16.-A solar grain dryer constructed of thin clear plastic to heat natural air to dry high moisture content grain. Grain drying may be the farm process most likely to make practical use of solar heat. Hay drying Hay drying is like grain drying, except that even less temperature rise in the air is needed. Therefore, a similar system could be used. Curing tobacco and sweetpotatoes Bright leaf tobacco curing requires a considerable quantity of moderately low-temperature heat during the summer when solar radiation is usually high. This heat must be controlled accurately and must be supplied continuously, varying only as the stage of cure dictates. Therefore, some form of heat storage, supplemental heat, or both, is required if solar energy is to be used for tobacco curing. Sweetpotato curing requires less heat at a lower temperature than tobacco curing. Furthermore, it is permissible to supply heat during daylight only. Otherwise, the heating system would be similar to that for tobacco curing. Heating other farm structures The use of heat for livestock shelters in the South, except for brooding poultry and small animals, has not yet been shown to improve production. If such heating is of economic value, it can be accomplished with solar energy and heat storage. Poultry brooding can be done with heat from a flat-plate collector, but heat storage or supplemental heat would have to be provided. An experimental poultry house in Pennsylvania has been heated in winter with solar heat and a satisfactorily low moisture level was maintained (6). Water heating Various models of solar heaters have been used for heating water. There is no doubt that they will work satisfactorily; the question is whether they are more economical than conventional means. Open waterers for livestock can take advantage of solar heating in winter if the sides and bottoms are painted black (fig. 17). Heating plant beds and greenhouses Plant beds and greenhouses generally receive adequate solar heat during daylight, but require supplemental heat at night. Some method of heat storage might prove practical for this application. Cooking Solar cookstoves, intended for use in such countries as India, where fuels are scarce and sunshine is abundant, have been designed to sell for about $5. It appears possible that a solar stove could be adapted for cooking feed for livestock since the cooking would not need to be done on as strict a schedule as it usually is for humans. Cooling farm buildings The use of heat for cooling is demonstrated in the absorption-cycle refrigeration system, where heat from steam or from a gas flame is applied to the generator. Heat from a solar collector could furnish this energy. Whether a flat-plate or a concentrating collector would be best suited for this purpose depends on the temperature required at the generator of the absorption unit. Such an application of solar heat would appear very desirable, because the insolation rate is highest when the cooling load is greatest. Furthermore, cooling at night is often not required. There are indications that summer cooling for poultry and livestock may result in improved production and the economy of artificially cooling farm buildings is now being studied. If cooling proves effective, solar heat may economically furnish the required energy. A solar-operated absorption cooling system was studied at Purdue University with a 150-square-foot receiver area. This type of unit, which would be applicable to environmental cooling and air conditioning, provided coefficients of performance ranging from 0.50 to 0.63 (34). Storing solar energy Storage of solar energy may be the key to future survival. The sun does not shine at night, sometimes not for days. Research is underway in Kansas and Georgia by the USDA on materials, methods, and applications of solar energy storage. INSECT CONTROL WITHOUT CHEMICALS Electric light traps may provide future insect-free living. Many injurious insects are attracted to ultraviolet light and can be trapped and destroyed before they lay their eggs and before they damage crops. Recent reports from the Purdue Agricultural Experiment Station, based on several years of research on relative attractiveness of various lamps, have indicated that this is a satisfactory way to destroy insects in gardens. Light in the near ultraviolet region of the sprectrum is most attractive to insects. This light, not visible to man, is called black light. Research workers found that a light trap with three 15-watt blacklight lamps protected corn, potatoes, tomatoes, and cucumbers from insect damage in 50- by 60-foot garden plots. The black-light traps controlled striped and spotted cucumber beetles, two serious insect pests of cucumbers. Traps also prevented bacterial wilt of cucurbits, since this disease is transmitted only by these beetles. In North Carolina, 366 black-light traps are being used in a 113square-mile area to determine their effectiveness in controlling tobacco horn worms. This study is based on a small-scale experiment previously conducted. Fuel cell ENERGY SOURCES FROM NEW MATERIALS Thermodynamically, fuel cells are constant temperature, constant pressure devices, and the maximum energy yield is equal to the change in free energy between products and reactants. For most fuel cells, such as hydrogen and the hydrocarbons, with air or oxygen as oxidant, the free energy change near room temperature is almost as large as the heat of combustion of the fuel. Thus, theoretical efficiencies, expressed as a percentage of the heat of combustion, approach 100 percent. In practice, efficiencies substantially higher than 50 percent are fairly common in laboratory cells; as high as 80 percent has been reported. High efficiency usually is the most important consideration in choosing fuel cells over other energy conversion devices for a given application. Another important consideration is the possibility of operating at low ambient temperatures. Fuel cells are not heat engines like thermoelectric and thermionic devices and conventional steam turbogenerators. Therefore, they are not limited by the Carnot efficiency that limits heat engines. High temperatures are not necessary to increase efficiency, but are used in some fuel cells to make ordinarily unreactive fuels more reactive, or to increase the current output. Since a high-temperature molten carbonate cell currently is the best contender for future large-scale industrial use, problems associated with series connections, corrosion, and electrolyte losses become formidable. Even so, according to investigators at Leesona Moos Laboratories, Jamaica, N.Y., the molten carbonate Carbox (R) cell can be built for about $100 to $250 per kilowatt-hour capacity, or about $2 per pound of weight. Most current efforts in civilian fuel cell applications involve propulsion of automobiles and other vehicles. It is not yet clear what type of cell is best suited for this purpose, or what type of fuel will have to be produced in quantity to meet the demand. At the moment, propane and methyl alcohol are good prospects because they are liquids and contain large amounts of energy per unit of volume, and they may not be too expensive to produce. A tractor powered by fuel cells that will pull a multibottom plow has been demonstrated. The advantages of fuel cells for automobiles are lack of smoke and noise, few moving parts, less wear, and a more simplified automobile design. One conceptual design of a mass-produced car has been prepared by Brooks Stevens Associates, Milwaukee, Wis., and is based on the assumption that fuel cells can be housed within the wall thickness of the body shell. An early return of electric cars has been predicted rather freely. If true, the advent of a fuel-cell car will be speeded, since the two would be similar technologically. The biochemical fuel cell The biochemical fuel cell (10) is an electrochemical generator in which micro-organisms carry out the chemical reaction to produce electric power. Organic or inorganic material may be used by a micro-organism in its catebolic process. The current produced is proportional not only to the rate of metabolism of micro-organisms and the number of micro-organisms taking part in the reaction, but also to the number of electrons released in the particular reaction. Micro-organism fuel cells have an efficiency of approximately 50 percent and they may produce more power than ordinary fuel cells. They can use waste products and for this reason may become important in this Nation's materials and resources. Thermoelectricity The thermoelectric generator can use waste heat energy or solar energy to produce electric power. The first thermoelectric generator made of ceramics (14) was developed for the Army by Minneapolis-Honeywell Co. It is capable of operating at unusually high temperatures-up to 2,400° F.-which produces four times the voltage of presently available thermoelectric generators. A pilot model is designed to deliver 100 volts open circuit. |