SOLAR ENERGY INTRODUCTION SOLAR ENERGY is the radiant energy that we receive from the sun in the form of heat and light. It is an inexhaustible source of energy. Solar Energy is the ultimate source of most of the sources of energy that we use. The wind energy, water energy, energy of fossil fuels and the energy in food are due to solar energy. SOURCE OF SOLAR ENERGY The discovery of radioactivity led some scientists to suggest that the energy released during radioactive decay of radioactive materials in the sun, might be the source of solar energy.
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As the liberation of energy from this is extremely slow, the hypothesis was rejected. Some scientists suggested that the thermonuclear reactions could be the source of solar energy. This could explain the observed radiations from the sun. The most convincing explanation was given by Hans Bethe and C. von Weizsacker. Bethe suggested that the reaction in which hydrogen nuclei fuse to form helium nuclei is the source of solar energy of the sun. In this process, enormous amount of energy is released. REACTIONS IN THE SUN There are two different cycles of processes.
One is the proton-proton chain or p-p chain. The other is the Carbon Cycle or CNO cycle (Carbon-Nitrogen-Oxygen) or sometimes Bethe- Weizsacker-cycle. Proton-Proton chain: The proton–proton chain reaction is one of the fusion reactions in which four Hydrogen nuclei fuse into one Helium nucleus with the release of enormous amount of energy in the form of Gamma rays. Carbon Cycle: Carbon cycle, CNO cycle (Carbon-Nitrogen-Oxygen), or sometimes Bethe-Weizsacker-cycle, is a fusion reactions by which stars convert hydrogen to helium. The Carbon cycle is a catalytic cycle.
In the carbon cycle, the carbon atom acts as a nuclear catalyst. NATURAL TRANSFORMATION OF SOLAR ENERGY Many of the useful sources of energy come from the natural transformation of solar energy. They are: * Wind Energy * Water Energy * Energy in food * Energy of fossil fuels (a) (b) Wind Energy: Solar energy heats the air near the earth. The hot air becomes lighter and this air rises up. This results in low pressure area. Cooler air flows into this region giving rise to wind currents. Thus wind energy is due to solar energy.
Wind energy is harnessed for many useful purposes such as production of electricity, sailing of boats etc. (c) Water Energy: Solar energy causes water to evaporate from water bodies. The water vapor rises to form clouds and the clouds bring rain. The rainwater flowing downhill possesses kinetic energy. This energy can be used to generate hydroelectricity. Thus solar energy is also responsible for water energy. (d) Energy in food: Plants use sun light along with Carbon dioxide and water for production of food during Photosynthesis. This food due to solar energy maintains every form of life on earth.
Energy of fossil Fuels: The fossil fuels are formed when living things get embedded in the earth’s crust and undergo chemical change. Life forms are due to solar energy. Thus fossil fuels are also due to solar energy. SOLAR DEVICES Nearly one third of the solar radiation consists of infrared radiation. Heat from the sun reaches the earth in the form of infrared radiation. Although a lot of energy from the sun reaches the earth, we use only a part of it. Rapid depletion of fossil fuels has promoted the development of technology to harness solar energy.
As a result a number of solar energy devices have come into existence. Solar devices: The devices used to harness solar energy are called solar devices. Solar devices are classified into two types based on their principle of working. They are Solar energy is converted into heat energy. Example: Solar cooker and Solar water heater. Solar energy is converted into electricity. Example: Solar cell. (a) Solar cooker: Solar cooker is a simple device used to cook food. It is made of a wooden box or heat resistant material. The inside of the box is painted black.
The box is covered with a transparent plate of glass. A plane mirror is fitted to the inner surface of the box. Food to be cooked is taken in a metal container. It is placed inside the box. The cooker is placed such that the sun’s rays are incident on the mirror. The mirror reflects the solar radiations on to the container. This raises the temperature of the food and the food gets cooked. The black paint on the inside walls of the box and the outer surface of the container ensures better absorption of solar energy. The glass plate does not allow the heat to flow out of the box.
Thus the heat energy, trapped inside, the container is used for cooking food. A Peculiar property of glass: Glass has a peculiar property. Plain glass is transparent to light and infrared rays of shorter wavelength. But it is opaque to infrared rays of longer wavelength. Infrared rays of the shorter wavelength are absorbed and the inside of the box emits infrared rays of longer wavelength, which will be retained inside the box and thus helps in cooking of the food. (b) Solar water heater: Solar water heaters are designed on the same principle as of solar cookers.
In solar water heaters, a copper pipe with its outer surface painted black is fixed in the form of a coil in a box similar to that of a cooker. Bending copper pipe as a coil helps to increase the area for absorption of solar energy. A reservoir kept at higher level stores water. This is connected to a small cylindrical tank kept at a slightly higher level above the heater. One end of the copper pipe is connected to the bottom of the small tank with the other end connected near its middle. Water from the tank flows continuously through the pipe.
The water absorbs heat and gets heated up. Hot water remains in the upper portion of the tank and this can be drawn through a tap. Cold water from the reservoir tank replaces the hot water drawn. (c) Solar Cells: The devices that convert solar energy into electrical energy are called solar cells. A common solar cell consists of a small piece of light absorbing material like silicon. Solar energy entering silicon releases electrons from Silicon atom to produce electricity. The voltage produces is about 0. 5 V and the power produced is 0. 7 Watt.
To obtain higher voltage and power, a large number of cells are connected in series. This arrangement of cells is known as solar panel. In spite of low efficiency and high cost of pure Silicon, solar cells are used for many purposes. They are the main source of energy in artificial satellites. They are also used as a source of energy for radio or wireless transmission, at TV relay stations, traffic lights, street lights and research centre in remote areas. They may be called as the future source of electricity and may solve the problem of energy crisis. BIBLIOGRAPHY: * Textbook * Internet