Page 5 - Sources of Energy

In order to produce hydel electricity,
high-rise dams are constructed on the river
to obstruct the flow of water and thereby
collect water in larger reservoirs. The water
level rises and in this process the kinetic
energy of flowing water gets transformed into
potential energy. The water from the high
level in the dam is carried through pipes, to
the turbine, at the bottom of the dam
(Fig. 14.3). Since the water in the reservoir
would be refilled each time it rains (hydro
power is a renewable source of energy) we
would not have to worry about hydro
Figure 14.3 electricity sources getting used up the way
A schematic view of a fossil fuels would get finished one day.
hydro power plant But, constructions of big dams have certain problems associated
with it. The dams can be constructed only in a limited number of places,
preferably in hilly terrains. Large areas of agricultural land and human
habitation are to be sacrificed as they get submerged. Large eco-systems
are destroyed when submerged under the water in dams. The vegetation
which is submerged rots under anaerobic conditions and gives rise to
large amounts of methane which is also a green-house gas. It creates
the problem of satisfactory rehabilitation of displaced people. Opposition
to the construction of Tehri Dam on the river Ganga and Sardar Sarovar
project on the river Narmada are due to such problems.

14.2.4 Improvements in the Technology for using
Conventional Sources of Energy

Bio-Mass
We mentioned earlier that wood has been used as a fuel for a long time.
If we can ensure that enough trees are planted, a continuous supply of
fire-wood can be assured. You must also be familiar with the use of
cow-dung cakes as a fuel. Given the large live-stock population in India,
this can also assure us a steady source of fuel. Since these fuels are
plant and animal products, the source of these fuels is said to be
bio-mass. These fuels, however, do not produce much heat on burning
and a lot of smoke is given out when they are burnt. Therefore,
technological inputs to improve the efficiency of these fuels are necessary.
When wood is burnt in a limited supply of oxygen, water and volatile
materials present in it get removed and charcoal is left behind as the
residue. Charcoal burns without flames, is comparatively smokeless and
has a higher heat generation efficiency.
Similarly, cow-dung, various plant materials like the residue after
harvesting the crops, vegetable waste and sewage are decomposed in
the absence of oxygen to give bio-gas. Since the starting material is mainly
cow-dung, it is popularly known as ‘gobar-gas’. Bio-gas is produced in
a plant as shown in Fig. 14.4.

246 Science