Solar Radiation is an energy resource many times larger than man’s energy needs. Man has been able to make us of this resource only on a limited scale, mainly for drying crops and producing salt from brines. However, environmental pollution, increasing energy demands, and rising costs of fuels have led to considerable interest in solar energy for additional uses, not only in highly industrialized but also in developing countries. The most basic forms of the energy from the sun are light and heat.The sun is a sphere of intensely hot gaseous matter. In its interior a continuous fusion process occurs in which hydrogen nuclei combine to from helium nuclei. The mass of the helium is less than that of the hydrogen, so some mass is always being converted to energy. This energy is radiated out from the surface of the sun, and an extremely small fraction of its intercepted by the earth. The average intensity of this radiation just outside the earth’s atmosphere, 93 million miles from the sun is 1.36 kilowatts per square meter. This value is called the solar constant.Solar energy is absorbed, scattered, reflected by the atmosphere. It reaches the ground as diffuse radiation, which comes from the many directions, or as beam radiation, which comes from the direction of the sun. On a very clear day, the atmosphere may transmit 90% of the solar radiation. Most of this transmitted radiation is beam radiation. On a very cloudy day the atmosphere may transmit less than 10% of the solar radiation. All of this transmitted radiation is diffuse radiation. The solar energy reaching the ground has a maximum intensity of about 1.2 kilowatts per square meter, or about 1.3 horsepower per square yard. Almost half this solar energy is visible light, about half is near infrared radiation, and a very small percentage is in the form of ultraviolet radiation.The ancient Chinese, Egyptians, Phoenicians, Greeks and Romans used solar energy to evaporate alt water to produce salt. Solar crop drying is also an ancient art.The first major solar still was built at Las Salinas, Chile, in 1872. It operated for about 30 years, had a total area of more than an acre and was used to produce drinking water for animals used in nitrate mining.In 1913, Egypt provided a parabolic collector to provide a steam to run engine for pumping irrigation water from the Nile. One of the first solar- heated houses was built by Massachusetts Institute of Technology at Cambridge, Mass, in 1939. It was the first in the series of experimental solar houses.Chemical and Biological Conversion of Solar EnergySolar radiation can be converted to chemical energy by photochemical processes. An ideal photochemical reaction would absorb as much as possible of the solar energy spectrum in bringing about an energy- storing or endothermic chemical reaction. For practical applications, it must also be possible to reverse the reaction to recover the energy and save the chemicals for reuse. The reaction might produce a single compound that could be stored and reacted at a later time, or the reaction might yield two or more products that could be separated and later recombined to recover energy. The chemicals in the reaction must be inexpensive and easy to handle.Conversion of Solar Energy to Thermal EnergySolar radiation of all wavelengths can readily be converted to thermal energy by using a black surface to absorb the radiant energy. Two kinds of devices are used to intercept solar radiations and convert it to thermal energy: a flat-plate collector and a focusing collector.The uses of converting solar energy to a thermal energy are for heating the pools, for drinking a hot water, and heating a space for buildings.Flat- Plate Collectors uses a blackened plate and tubes or fins arranged so that a fluid can pass by the plate and puck up heat from it. It is mounted in a fixed position, and it absorbs both beam and diffuse radiation. It can operate temperature up to 125 degree Fahrenheit above daytime air temperature at the site. It is a practical device. Its heated surface can be used for water heating, house heating, air conditioning, evaporation of salt, water, and distillation of salt or brackish water to produce drinking water.Focusing Collectors uses a concave reflector or lens to concentrate solar beam radiation, thereby raising its intensity by 2 to 10,000 times. The focused radiation is absorbed on a blackened small receiver, which may be insulated to reduce thermal losses. The higher energy flux at the receiver allows energy collection at temperatures ranging from about 200 degree Fahrenheit to about 5000 degree Fahrenheit. A focusing collector must be movable so that it can be oriented to gather sunlight. No long time practical applications of focusing systems have yet been made, partly because it is difficult to maintain a highly reflective surface in the atmosphere over a long period of time. However, focusing collectors have been used in short term applications involving very high temperatures. In such cases, they are called as solar furnaces. Solar Furnaces are a precise optical instrument for concentrating beam radiation on very small targets to produce high energy fluxes and high temperatures. It usually consists of an accurate parabolic reflector to focus the radiation, a tracking system to align the axis of the paraboloid and the incoming beam radiation, a shutter mechanism to control the radiation, and a receiver or target-holding device. Solar Furnaces are useful in studying the high temperature properties of materials such as metal oxides and in exposing materials to intense thermal shock.Conversion of Solar Energy to Electrical EnergyMuch of the world’s energy needs must be met by using energy in its electrical or mechanical form. However, conversion of solar energy to electrical or mechanical energy is much more difficult to do economically than is the conversion of solar energy to thermal energy.Solar Cells are a solid state device that directly converts energy of solar radiation to electrical energy. Solar cells have been developed primarily for providing electric power for spacecraft. They work as well as well in small sizes as in large, and they operate for very long times if protected from damage. They can convert solar energy to electrical energy at efficiencies of 12% to 14%. Solar cells made of cadmium sulfide can be made thinner and lighter than silicon cells, but they have a maximum efficiency of about 6%.Heat engines can be used to convert solar energy to mechanical energy, which can then be used directly or converted to electrical energy by conventional techniques. Collectors are used to heat a working fluid such as steam, which then passes through an engine where part of its energy is converted to mechanical energy. The higher the temperature of the fluid supplied to the engine from the collector, the more efficient is the engine. On the other hand, collectors work best at lower temperatures. Flat- plate collectors are practical, but they are low-temperature devices. Thus, supplying energy from them to the engines means low engine efficiencies and very large collectors to achieve useful power outputs. Focusing collectors can heat fluids to higher temperatures and provide better engine efficiencies but practical and economical focusing collectors are yet to be developed.Photovoltaic Cell is the transformation of the sun’s light to electricity by using PVs Cell or the Photovoltaic Cell. It is not a device that was developed by using alloys of silicon. It is the most basic foundation of a PV system.The successful development of solar power systems could open many new applications and meet many energy needs. On a very large scale solar energy might contribute to regional or national electric power generating capacity. On a smaller scale, important needs such as pumping irrigation water might be met.Solar Thermal Plants, this is the plant that uses the suns light or rays to heat a liquid that likely produces steam. This steam is then developed or changed into a mechanical energy to be use for a generator along with the turbine. The three classification of solar- thermal power being used in a solar thermal plant are the solar dish, solar power tower and the solar dish.
Solar Energy Essay
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