The
Sun, one of the 200 billion stars of our galaxy milky-way and the nucleus of
our solar system is the core source of light and energy and also responsible
for existence of living in this planet. Every forms of energy found in this
planet are directly or indirectly depend on the sun. For instance, the
nutrients for our energies and daily activities come from animals and plants. These
animals depend on plants for their foods. Now, these plants need sunlight for
preparing their food using photosynthesis. Hence, we indirectly get nutrients
from the sun. Another example can be cited to illustrate the direct use of
sunlight. Our body needs vitamin D to
absorb calcium and
promote bone growth. Deficiency to this vitamin may cause breast cancer, colon
cancer, prostate cancer, heart disease, depression, weight gain, and other
maladies. 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 examples
visualize the importance of sun power in our life and hence, it is called
“Eternal Source of Energy”. Some examples are given below to elaborate this notion
further.     

At
Bronze Age, wheel, which was regarded as one of the revolutionary invention of human
civilization, had been introduced in animal cart in order to carry heavy load
and 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 coal
is used as a fuel to run the boiler. However, coal is an inferior form of fossil
fuel, since most of the energy are being wasted to heat the surrounding
environment and hence, make it less efficient form of fuel. This led the
researchers and scientists to invent the petrol and diesel engine, which were
internal combustion engines. Additionally, petrol and diesel were used as fuel
in these engine, which are high efficiency fossil fuel. Furthermore, gas turbine
were also used in industry for large scale production. These fossil fuel such
as coal, gas, petroleum, and diesel are formed due to the anaerobic decomposition
of buried dead organisms, which contain energy originating in ancient
photosynthesis. Hence, these fossil fuels are also harvested from sun power.    

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However,
these fossil fuels are enriched in carbon. Therefore, combustion of these
fossil fuel increase carbon-di-oxide that are presented in air. Increased
amount 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 more
popular, since electricity is a clean and environment friendly source of energy
and its consumption are more flexible and efficient. Hence, large amount of
electricity is needed. According to the current statistic, the world
electricity consumption is 25000 tera-watt-per hour. This large amount of
electricity is generated using fossil fuel such as coal and gas turbine and
thus, results in the depletion of these fossil fuel. Thus, several sustainable
and renewable energy sources such as wind, hydro-power, solar, solar thermal,
and biomass are gaining popularity nowadays, which are also directly or
indirectly depended on the sun power.

Wind
is renewable source of energy, where the wind energy is first converted to
mechanical energy by a wind turbine, and then to electrical energy by a
suitable generator. According to the current data, the world produces 486,790 mega-watt
from wind energy. This wind energy is also indirectly depended on the sun
power. For instance, different portions of the earth absorb different amount of
energy from the sun light due to their different angel of inclination. Like,
equatorial region gets direct heat from sun, whereas polar region gets inclined
heat. Hence, global winds are resulting from the difference in absorption of
solar energy between the climate zones on earth.

Hydro-power
is also a renewable source of energy, which is also indirectly depended on the
sun. For example, solar energy evaporates water from various water bodies such
as sea, ocean, river etc. Later, these evaporated waters fall as rains. These
rains can be stored behind dams, where its motion is used to generate
electricity 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 very
essential for animal and plant worlds.

Photovoltaic
is the largest source of renewable source of energy, which is directly depended
on sun power. Photovoltaic is consisted of several semiconductor cells, where
conversion of sun light to the electricity is done through semi-conductor
material using the photo-electric effect. The photovoltaic is commonly termed
as solar panel and it is also possible to meet all the electricity demand of
the world using these solar panels. However, the installation cost of these
panels are very high and the efficiency of energy conversion is quite low,
which results in producing 75 giga-watt of
world electricity. These solar panel may be installed in rooftop or open field
and sun tracker (i.e. which is used to follow the position of the sun, since
sun positions varies with time) may be used to increase its efficiency. As
photovoltaic has huge prospect, recently many research works have been going on
in this field.

Solar-thermal
is a renewable source of energy, which is also directly depended on the sun
power. The thermal energy from the sun is collected using a collector,
typically this collector is hot water panel. Sun radiation are concentrated
using mirror or lens to make heating more efficiently and effectively. Later,
this heated fluid is used to generate electricity using turbine-coupled
generator. Although this method currently does-not produce large amount of world
electricity, this has a great prospect and hence, several researches are going
on nowadays.

Biomass,
consisting of organic materials comes from plants and animals is a renewable
source of energy and also indirectly depends on sun power. Plants absorb the
sunlight in a process called photosynthesis. When these biomasses are burned,
the chemical energy in biomass is released as heat. Biomass can be burned
directly or converted to liquid biofuels or biogas that can be used as fuels.

Other
than the sources of energy, plants and animals life are greatly depended on the
sun. 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.