Transformation of solar energy
You
have already discovered that energy cannot be created or destroyed. Where
does energy come from? The answer is that on Earth the primary source
of energy is the Sun. The Sun is an enormous nuclear reactor producing
energy by destroying matter in a process called nuclear fusion. In this
process, hydrogen atoms are fused or joined to make larger atoms and the
energy produced is radiated into the Universe as electromagnetic radiation.
The Earth, being close to the Sun, receives a small portion of this radiated
energy.
Energy from the Sun - solar energy
The solar energy arrives at the Earth's atmosphere ranging from radio
waves through visible to gamma radiation. (See Electromagnetic
spectrum for more information) It is this solar energy that is transformed
into the range of energies we rely on here on the Earth. Without the Sun,
we would soon be a dead planet.
Solar power to electricity
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With
solar cells it is possible to transform the Sun's energy into
electrical energy. This is particularly valuable where other sources
of electrical energy are not available, for example, a telephone
box way out in the bush. Solar cell generated electrical energy
can also be transformed to kinetic energy, as is done with solar
powered cars.
A more common use of energy from the Sun is to generate electrical
energy by water flowing from lakes or dams. In this case, there
is a chain of transformations. First, the Sun's energy evaporates
water from the ocean or lakes. This water vapour rises, gaining
gravitational potential energy. Clouds form and the falling rain
experiences the transformation of potential to
kinetic energy. Water collected in dams above sea level still has
gravitational potential energy. Water flowing down from the dam
through a generator, transforms the stored gravitational potential
energy of the water, into kinetic energy of the moving turbine blades
in the generator, which is, in turn, transformed into electrical
energy. It is a long chain, all begun by the Sun.
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Food energy
We all need food to maintain life. The energy in food is chemical
energy which is transformed into thermal energy to keep us warm, to drive
our internal functions and, with children, to grow. Plants use energy
from the Sun's combined with carbon dioxide and water to produce food
by a process called photosynthesis. Plants are chemical factories storing
energy in the form of sugars so that it can be transformed at a later
time.
Stored
energy from the past
Energy from food keeps us warm inside and helps maintain our bodies, but
we also need an external source of storable energy to run our machines
and make our lives more comfortable. This energy can come from plants
too, but in a slightly different way. A wood fire burns plant material,
largely from trees that have stored solar energy over many years. Coal
is even older and is the compressed remains of plants millions of years
old. When we burn coal we are using the Sun's energy. Oil is thought to
have come from tiny sea creatures, their gathered energy trapped for millions
of years under the ground in the form of crude oil and natural gas. This
stored energy is transformed by machines into light, thermal energy, kinetic
energy and electrical energy to carry the transformation chain even further.
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