Presentation on Solar Energy
Uploaded by surfchick on Dec 29, 2004
Presentation Dialogue
SOLAR ENERGY. All life on Earth depends on energy from the sun. Solar energy is the source of energy for photosynthesis. It provides the warmth necessary for plants and animals to survive. The heat from the sun causes water on the Earth's surface to evaporate and form clouds that eventually provide fresh rainwater.
Solar energy is the result of thermonuclear fusion reactions deep within the sun. These reactions produce so much energy that they keep the surface temperature of the sun at about 10,300B0F (5,700B0C). Even though solar energy is the largest source of energy received by the Earth, its intensity at the Earth's surface is actually very low due to the large distance betwee n the Earth and the sun and the fact that the Earth's atmosphere absorbs and scatters some of the radiation. Even on a clear day with the sun directly overhead, the energy that reaches the Earth's surface is reduced about 30 percent by the atmosphere. When the sun is near the horizon and the sky is overcast, the solar energy at ground level can be negligible. It also varies from one point to another on the Earth's surface.
Nevertheless, in the 20th century, the sun's energy has become an increasingly attractive source for small amounts of direct power to meet human needs. A number of devices for collecting solar energy and converting it into electricity have been developed, and solar energy is used in a variety of ways. Solar energy is used to heat houses, and in many countries specially designed solar ovens are used for cooking. The sun also supplies energy to electric generators that provide power for weather and communications satellites and for radio and television equipment.
Because the intensity of the sun's radiation at the surface of the Earth is so low, collectors designed to capture solar energy must be large. In the sunniest parts of the continental United States, for example, in orde r for a collector to gather enough energy to serve one person for one day, the area of the collector's surface must be about 430 square feet (40 square meters). The actual energy that can be used depends on the efficiency of the collector and of the device that converts the radiation into usable energy.
Flat-plate collectors. The most common flat-plate collectors consist of a dark metal plate, covered with one or two sheets of glass, that absorbs heat. The heat...