Page 6 - Sources of Energy

The plant has a dome-like structure built with
bricks. A slurry of cow-dung and water is made in
the mixing tank from where it is fed into the digester.
The digester is a sealed chamber in which there is no
oxygen. Anaerobic micro-organisms that do not
require oxygen decompose or break down complex
compounds of the cow-dung slurry. It takes a few
days for the decomposition process to be complete
and generate gases like methane, carbon dioxide,
hydrogen and hydrogen sulphide. The bio-gas is
Figure 14.4
stored in the gas tank above the digester from which
Schematic diagram of a bio-gas plant
they are drawn through pipes for use.
Bio-gas is an excellent fuel as it contains up to 75% methane. It
burns without smoke, leaves no residue like ash in wood, charcoal and
coal burning. Its heating capacity is high. Bio-gas is also used for lighting.
The slurry left behind is removed periodically and used as excellent
manure, rich in nitrogen and phosphorous. The large-scale utilisation
of bio-waste and sewage material provides a safe and efficient method of
waste-disposal besides supplying energy and manure. Do you think
that bio-mass is a renewable source of energy?

Wind Energy
We saw in Class IX how unequal heating of the landmass
and water bodies by solar radiation generates air movement
and causes winds to blow. This kinetic energy of the wind
can be used to do work. This energy was harnessed by
windmills in the past to do mechanical work. For example,
in a water-lifting pump, the rotatory motion of windmill is
utilised to lift water from a well. Today, wind energy is also
used to generate electricity. A windmill essentially consists
of a structure similar to a large electric fan that is erected at
some height on a rigid support (Fig. 14.5).
To generate electricity, the rotatory motion of the windmill
is used to turn the turbine of the electric generator. The
output of a single windmill is quite small and cannot be used
for commercial purposes. Therefore, a number of windmills
are erected over a large area, which is known as wind energy
farm. The energy output of each windmill in a farm is coupled
together to get electricity on a commercial scale.
Figure 14.5 A windmill

Do You Know? Denmark is called the country of ‘winds’. More than 25% of their electricity needs are

generated through a vast network of windmills. In terms of total output, Germany is
the leader, while India is ranked fifth in harnessing wind energy for the production of
electricity. It is estimated that nearly 45,000 MW of electrical power can be generated if
India’s wind potential is fully exploited. The largest wind energy farm has been
established near Kanyakumari in Tamil Nadu and it generates 380 MW of electricity.

Sources of Energy 247