Solar Energy Essay Research Paper Presentation DialogueSOLAR

Solar Energy Essay, Research Paper

Presentation DialogueSOLAR ENERGY. All life on Earth depends on energy from the sun. Solarenergy is the source of energy for photosynthesis. It provides the warmthnecessary for plants and animals to survive. The heat from the sun causeswater on the Earth’s surface to evaporate and form clouds that eventuallyprovide fresh rainwater. Solar energy is the result of thermonuclear fusion reactions deepwithin the sun. These reactions produce so much energy that they keep thesurface temperature of the sun at about 10,300B0F (5,700B0C). Even though solarenergy is the largest source of energy received by the Earth, its intensityat the Earth’s surface is actually very low due to the large distance betweenthe Earth and the sun and the fact that the Earth’s atmosphere absorbs andscatters some of the radiation. Even on a clear day with the sun directlyoverhead, the energy that reaches the Earth’s surface is reduced about 30percent by the atmosphere. When the sun is near the horizon and the sky isovercast, the solar energy at ground level can be negligible. It also variesfrom one point to another on the Earth’s surface. Nevertheless, in the 20th century, the sun’s energy has become anincreasingly attractive source for small amounts of direct power to meethuman needs. A number of devices for collecting solar energy and convertingit into electricity have been developed, and solar energy is used in avariety of ways. Solar energy is used to heat houses, and in many countriesspecially designed solar ovens are used for cooking. The sun also suppliesenergy to electric generators that provide power for weather andcommunications satellites and for radio and television equipment.Because the intensity of the sun’s radiation at the surface of theEarth is so low, collectors designed to capture solar energy must be large.In the sunniest parts of the continental United States, for example, in orderfor a collector to gather enough energy to serve one person for one day, thearea of the collector’s surface must be about 430 square feet (40 squaremeters). The actual energy that can be used depends on the efficiency of thecollector and of the device that converts the radiation into usable energy. Flat-plate collectors. The most common flat-plate collectors consistof a dark metal plate, covered with one or two sheets of glass, that absorbsheat. The heat is transferred to air or water, called carrier fluids, thatflows past the back of the plate. This heat may be used directly or it may betransferred to another medium. Flat-plate collectors are used for home andhot-water heating . Flat-plate collectors typically heat carrier fluids totemperatures ranging from 150B0 to 200B0F (66B0 to 93B0C). The efficiency of suchcollectors varies from 20 to 80 percent.Concentrating collectors. When higher temperatures are required, aconcentrating collector is used. These collectors reflect and concentratesunlight from a wide area. One such device, called a solar furnace, wasinstalled in the Pyrenees in France and has several acres of mirrors focusedon a single target. The energy concentrated at the target is 3,000 times thatreceived by any single mirror, and the unit produces temperatures of up to3,630B0F (2,000B0C). Another structure, the so-called “power tower” plant nearBarstow, Calif., generates 10,000 kilowatts of electricity. Here, the furnaceacts as a boiler and generates steam for a steam turbine-electric generatorpower plant. In sophisticated concentrating collectors such as the Californiatower, each mirror is rotated by a heliostat that directs the sun’s rays fromthe mirror to the target. Positioning motors, drives, and controllers makesuch systems expensive. Less costly collectors can produce temperatures lowerthan those of more advanced concentrating collectors but higher than those offlat-plate collectors. For example, parabolic reflectors that concentratesunlight on black pipes can produce fluid temperatures of about 400B0 to 550B0F(200B0 to 290B0C) and can concentrate the solar energy up to 50 times itsoriginal strength.Small Stand-Alone DC SystemThe small stand-alone system is an excellent replacement for propaneor kerosene lights in a remote cabin, a recreational vehicle or a boat. Thesize of the photovoltaic (PV) array and battery will depend upon individualrequirements. The actual sizing methods are discussed elsewhere. The PV arraycharges the battery during daylight hours and the battery supplies power tothe loads as needed. The charge regulator terminates the charging when thebattery reaches full charge. The load center may contain meters to monitorsystem operation and fuses to protect wiring in the event of malfunction orshort circuit in the house.PV – Generator CombinationThe PV – Generator Combination system may be an economicalalternative to a large stand-alone PV system, because the PV array does nothave to be sized large enough for worst case weather conditions. A gasoline,propane or diesel generator combined with a battery charger can supply powerwhen the PV array falls short. If the PV array is sized for averageconditions, then during extended overcast situations or periods of increasedload, the generator can be started. When batteries are low, the generatorwill power the AC loads in the house as well as a battery charger to helprecharge the batteries. If the PV array is sized much smaller than needed fornormal use, the generator can power peak loads such as doing laundry or