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Solar Energy,The term "solar energy" most commonly refers to direct use of the sun's energy; by means of photovoltaic solar cells, which convert sunlight into electricity, and by the use of various devices and techniques to convert solar: radiation to heat that may be used for heating and cooling buildings, providing hot water for homes, businesses, and industry, and generating electricity by thermal means. Besides the direct conversion of sunlight into electricity by means of photovoltaic cells, sunlight may be, I used to generate steam, which can then be used to power a turbine for producing electricity. One solar-thermal design, called a power tower, consists of a field of movable mirrors that surround a tower, at the top of which is a boiler. The mirrors focus the light on the boiler. At the bottom of the tower is a building that houses a turbine-generator. A prototype 10-megawatt power tower, Solar One, constructed in California, began commercial operation in 1982. About 40% of the energy consumed by US industry .is used to provide temperatures of less than 315 degrees C. Such temperatures can be attained by using concentrating solar collectors that focus sunlight onto a pipe, onto a single point or through a Fresnel lens. Such collectors must track the sun as it moves across the sky in order to maintain proper focus of the light. Solar furnaces use large arrays of mirrors to achieve temperatures high enough for metallurgical work. The greatest public interest in solar energy has been directed toward its use in heating and cooling buildings. Residential and commercial solar applications may be divided into two types: active systems, which rely on solar collector panels; and passive design, by which a building is designed, situated and oriented so as to receive and store heat from the sun during the winter, but also to keep the sun out during the summer. Humanity's use of the sun's energy extends far back into prehistory. Many ancient and primitive cultures have exhibited a sophisticated knowledge of how to use solar energy to maintain comfortable temperatures inside dwellings. Adaptive architecture probably played an important role in the survival and success of human groups in prehistoric times. Coupled with the use of fire, solar shelter orientation probably made it possible for some human communities to remain in one place year-round rather than migrating with the changing of the seasons. Pesticides have also taken their toll. In 1947, new chemical poison called DDT was introduced. It proved very effective in controlling insect pests like the potato beetle and the boll weevil. But pesticides, which decompose very slowly, accumulate in animals which feed on pest insects or their predators, and the accumulated poisons attack their nervous systems. Pesticides also interfere with the formation of calcium in birds, which lay eggs with very thin shells or no shell at all. When wildlife fail to reproduce, it isn't very long before they disappear. Now suppose we take Canada. Every Canadian has 140 acres to roam around in. The Canadians use at the moment four acres, and they too have a large food surplus available for export. Looking through Glass links of London new arrivals ,Nobody knows for sure who invented the first spectacles or who wore the first pair. Various old I European coins of the Middle Ages were stamped with eyeglasses, symbolizing the ability links London new arrivals to see the truth.
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