TheSun, one of the 200 billion stars of our galaxy milky-way and the nucleus ofour solar system is the core source of light and energy and also responsiblefor existence of living in this planet. Every forms of energy found in thisplanet are directly or indirectly depend on the sun. For instance, thenutrients for our energies and daily activities come from animals and plants. Theseanimals depend on plants for their foods. Now, these plants need sunlight forpreparing their food using photosynthesis. Hence, we indirectly get nutrientsfrom the sun.

Another example can be cited to illustrate the direct use ofsunlight. Our body needs vitamin D toabsorb calcium andpromote bone growth. Deficiency to this vitamin may cause breast cancer, coloncancer, prostate cancer, heart disease, depression, weight gain, and othermaladies. 90% of this vitamin is made by our body using the ultra violet (UV)rays of sunlight passed through our skin. Thus, these above mentioned examplesvisualize the importance of sun power in our life and hence, it is called”Eternal Source of Energy”.

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Some examples are given below to elaborate this notionfurther.     AtBronze Age, wheel, which was regarded as one of the revolutionary invention of humancivilization, had been introduced in animal cart in order to carry heavy loadand transport from one place to another. Later, the invention of steam engine,an external combustion engine, replaced animal cart with vehicle. Moreover,steam engine led human civilization to enter into the industrial age, where coalis used as a fuel to run the boiler. However, coal is an inferior form of fossilfuel, since most of the energy are being wasted to heat the surroundingenvironment and hence, make it less efficient form of fuel. This led theresearchers and scientists to invent the petrol and diesel engine, which wereinternal combustion engines. Additionally, petrol and diesel were used as fuelin these engine, which are high efficiency fossil fuel. Furthermore, gas turbinewere also used in industry for large scale production.

These fossil fuel suchas coal, gas, petroleum, and diesel are formed due to the anaerobic decompositionof buried dead organisms, which contain energy originating in ancientphotosynthesis. Hence, these fossil fuels are also harvested from sun power.    However,these fossil fuels are enriched in carbon. Therefore, combustion of thesefossil fuel increase carbon-di-oxide that are presented in air. Increasedamount of carbon-di-oxide of the air causes global warming and green-house effect.

Hence, research has been made to search for a green and clean source of energy.Thus, electric motor, electric vehicle, and electric appliances became morepopular, since electricity is a clean and environment friendly source of energyand its consumption are more flexible and efficient. Hence, large amount ofelectricity is needed. According to the current statistic, the worldelectricity consumption is 25000 tera-watt-per hour. This large amount ofelectricity is generated using fossil fuel such as coal and gas turbine andthus, results in the depletion of these fossil fuel. Thus, several sustainableand renewable energy sources such as wind, hydro-power, solar, solar thermal,and biomass are gaining popularity nowadays, which are also directly orindirectly depended on the sun power. Windis renewable source of energy, where the wind energy is first converted tomechanical energy by a wind turbine, and then to electrical energy by asuitable generator.

According to the current data, the world produces 486,790 mega-wattfrom wind energy. This wind energy is also indirectly depended on the sunpower. For instance, different portions of the earth absorb different amount ofenergy from the sun light due to their different angel of inclination. Like,equatorial region gets direct heat from sun, whereas polar region gets inclinedheat. Hence, global winds are resulting from the difference in absorption ofsolar energy between the climate zones on earth.Hydro-poweris also a renewable source of energy, which is also indirectly depended on thesun. For example, solar energy evaporates water from various water bodies suchas sea, ocean, river etc. Later, these evaporated waters fall as rains.

Theserains can be stored behind dams, where its motion is used to generateelectricity via hydropower. Hydropower, according to the current information,share portion almost 10000 mega-watt of total world electricity. Furthermore,solar power is also responsible for the water-cycle in the earth, which is veryessential for animal and plant worlds.

Photovoltaicis the largest source of renewable source of energy, which is directly dependedon sun power. Photovoltaic is consisted of several semiconductor cells, whereconversion of sun light to the electricity is done through semi-conductormaterial using the photo-electric effect. The photovoltaic is commonly termedas solar panel and it is also possible to meet all the electricity demand ofthe world using these solar panels. However, the installation cost of thesepanels are very high and the efficiency of energy conversion is quite low,which results in producing 75 giga-watt ofworld electricity.

These solar panel may be installed in rooftop or open fieldand sun tracker (i.e. which is used to follow the position of the sun, sincesun positions varies with time) may be used to increase its efficiency.

Asphotovoltaic has huge prospect, recently many research works have been going onin this field.Solar-thermalis a renewable source of energy, which is also directly depended on the sunpower. The thermal energy from the sun is collected using a collector,typically this collector is hot water panel. Sun radiation are concentratedusing mirror or lens to make heating more efficiently and effectively. Later,this heated fluid is used to generate electricity using turbine-coupledgenerator.

Although this method currently does-not produce large amount of worldelectricity, this has a great prospect and hence, several researches are goingon nowadays.Biomass,consisting of organic materials comes from plants and animals is a renewablesource of energy and also indirectly depends on sun power. Plants absorb thesunlight in a process called photosynthesis. When these biomasses are burned,the chemical energy in biomass is released as heat.

Biomass can be burneddirectly or converted to liquid biofuels or biogas that can be used as fuels. Otherthan the sources of energy, plants and animals life are greatly depended on thesun. Hence, we may conclude that sun is called the eternal source of energy.That is why, in some religion, they also worship sun as a goddess.