THE ENERGY WE USE IN THE EARTH

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Solar Energy

I . Introduction

Solar Energy is the generated by the sun . This energy is in the form of electromagnetic radiation and travels to the earth in waves of various lengths . Some of the radiation becomes evident as heat , some as visible light . All life on earth depends ultimately on the sun 's radiation . It warms the earth and provides energy that green plants use to make their food (Without plants , there would be no animals , since all animals must feed on plants or

in plant-eating organisms (see What is Solar Energy

Since ancient times attempts have been made - with varying success - to put the energy from the sun to practical use . In the third century B .C the Greek mathematician and physicist Archimedes is said to have used the sun 's rays reflected from mirrors to set fire to an invading Roman fleet . In the 19th century , John Ericsson , designer of the ironclad warship Monitor , built an engine that was powered by the sun 's energy

Moreover , 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 (see HYPERLINK "http /www .questia .com /read ?title The 20Active 20Use 20of 20 Solar 20Energy " The Active Use of Solar Energy . 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 HYPERLINK "http /www .questia .com /SM .qst ?act adv contributors Rhone 20Resch dcontr ibutors Rhone 20Resch " Resch , 104-106 . The solar energy reaching the ground has a maximum intensity of about 1 .2 kilowatts per square meter or about 1 .3...