CONVENTIONAL SOURCES OF ENERGY
Fossil Fuels:-
fossil fuels – coal and petroleum.
But these fuels were formed over millions of years ago and there are only limited reserves.
The fossil fuels are non-renewable sources of energy, so we need to conserve them. If we were to continue consuming these sources at such alarming rates, we would soon run out of energy!
In order to avoid this, alternate sources of energy were explored. But we continue to be largely dependent on fossil fuels for most of our energy requirements
Burning fossil fuels has other disadvantages too.
the air pollution caused by burning of coal or petroleum products.
The oxides of carbon, nitrogen and sulphur that are released on burning fossil fuels are acidic oxides.
These lead to acid rain which affects our water and soil resources.
the green-house effect of gases like carbon dioxide.
Thermal Power Plant
Large amount of fossil fuels are burnt every day in power stations to heat up water to produce steam which further runs the turbine to generate electricity.
The transmission of electricity is more efficient than transporting coal or petroleum over the same distance
Therefore, many thermal power plants are set up near coal or oil fields.
The term thermal power plant is used since fuel is burnt to produce heat energy which is converted into electrical energy.
Hydro Power Plants
Another traditional source of energy was the kinetic energy of flowing water or the potential energy of water at a height.
Hydro power plants convert the potential energy of falling water into electricity.
a quarter of our energy requirement in India is met by hydro power plants.
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
Since the water in the reservoir would be refilled each time it rains (hydro power is a renewable source of energy)
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.
Improvements in the Technology for using Conventional Sources of Energy
Bio-Mass:-
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’.
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 stored in the gas tank above the digester from which 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 wastedisposal besides supplying energy and manure.
Wind Energy
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 .
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
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.
Wind energy is an environment-friendly and efficient source of renewable energy.
It requires no recurring expenses for the production of electricity. But there are many limitations in harnessing wind energy.
Firstly, wind energy farms can be established only at those places where wind blows for the greater part of a year.
The wind speed should also be higher than 15 km/h to maintain the required speed of the turbine.
Furthermore, there should be some back-up facilities (like storage cells) to take care of the energy needs during a period when there is no wind.
Establishment of wind energy farms requires large area of land.
For a 1 MW generator, the farm needs about 2 hectares of land. The initial cost of establishment of the farm is quite high.
Moreover, since the tower and blades are exposed to the vagaries of nature like rain, Sun, storm and cyclone, they need a high level of maintenance
ALTERNATIVE OR NON-CONVENTIONAL CONVENTIONAL SOURCES OF ENERGY
Solar Energy
India is lucky to receive solar energy for greater part of the year.
It is estimated that during a year India receives the energy equivalent to more than 5,000 trillion kWh.
Under clear (cloudless) sky conditions, the daily average varies from 4 to 7 kWh/m2.
A black surface absorbs more heat as compared to a white or a reflecting surface under identical conditions.
Solar cookers and solar water heaters use this property in their working. Some solar cookers achieve a higher temperature by using mirrors to focus the rays of the Sun.
limitation of using solar energy is overcome by using solar cells that convert solar energy into electricity
A typical cell develops a voltage of 0.5–1 V and can produce about 0.7 W of electricity when exposed to the Sun.
A large number of solar cells are, combined in an arrangement called solar cell panel (Fig. 14.7) that can deliver enough electricity for practical use.
The principal advantages associated with solar cells are that they have no moving parts, require little maintenance and work quite satisfactorily without the use of any focussing device.
Another advantage is that they can be set up in remote and inaccessible hamlets or very sparsely inhabited areas in which laying of a power transmission line may be expensive and not commercially viable.
Silicon, which is used for making solar cells, is abundant in nature but availability of the special grade silicon for making solar cells is limited.
The entire process of manufacture is still very expensive, silver used for interconnection of the cells in the panel further adds to the cost.
In spite of the high cost and low efficiency, solar cells are used for many scientific and technological applications.
Artificial satellites and space probes like Mars orbiters use solar cells as the main source of energy.
Radio or wireless transmission systems or TV relay stations in remote locations use solar cell panels.
Traffic signals, calculators and many toys are fitted with solar cells.
The solar cell panels are mounted on specially designed inclined roof tops so that more solar energy is incident over it.
The domestic use of solar cells is, however, limited due to its high cost.
Energy from the Sea
Tidal Energy:-
Due to the gravitational pull of mainly the moon on the spinning earth, the level of water in the sea rises and falls.. This phenomenon is called high and low tides and the difference in sea-levels gives us tidal energy.
Tidal energy is harnessed by constructing a dam across a narrow opening to the sea.
A turbine fixed at the opening of the dam converts tidal energy to electricity.
the locations where such dams can be built are limited.
Wave Energy :-
the kinetic energy possessed by huge waves near the seashore can be trapped to generate electricity.
The waves are generated by strong winds blowing across the sea.
A wide variety of devices have been developed to trap wave energy for rotation of turbine and production of electricity.
Ocean Thermal Energy
The water at the surface of the sea or ocean is heated by the Sun while the water in deeper sections is relatively cold.
This difference in temperature is exploited to obtain energy in ocean-thermal-energy conversion plants.
These plants can operate if the temperature difference between the water at the surface and water at depths up to 2 km is 20 K (20°C) or more.
The warm surface-water is used to boil a volatile liquid like ammonia. The vapours of the liquid are then used to run the turbine of generator.
The cold water from the depth of the ocean is pumped up and condense vapour again to liquid.
The energy potential from the sea (tidal energy, wave energy and ocean thermal energy) is quite large, but efficient commercial exploitation is difficult.
Geothermal Energy
Due to geological changes, molten rocks formed in the deeper hot regions of earth’s crust are pushed upward and trapped in certain regions called ‘hot spots’.
When underground water comes in contact with the hot spot, steam is generated. Sometimes hot water from that region finds outlets at the surface. Such outlets are known as hot springs.
The steam trapped in rocks is routed through a pipe to a turbine and used to generate electricity.
Nuclear Energy
In a process called nuclear fission, the nucleus of a heavy atom (such as uranium, plutonium or thorium), when bombarded with low-energy neutrons, can be split apart into lighter nuclei
When this is done, a tremendous amount of energy is released if the mass of the original nucleus is just a little more than the sum of the masses of the individual products.
The fission of an atom of uranium, for example, produces 10 million times the energy produced by the combustion of an atom of carbon from coal.
In a nuclear reactor designed for electric power generation, such nuclear ‘fuel’ can be part of a selfsustaining fission chain reaction that releases energy at a controlled rate
The released energy can be used to produce steam and further generate electricity
Nuclear power reactors located at Tarapur (Maharashtra), Rana Pratap Sagar (Rajasthan), Kalpakkam (Tamil Nadu), Narora (UP), Kakrapar (Gujarat) and Kaiga (Karnataka) have the installed capacity of less than 3% of the total electricity generation capacity of our country..
The major hazard of nuclear power generation is the storage and disposal of spent or used fuels – the uranium still decaying into harmful subatomic particles (radiations).
Improper nuclear-waste storage and disposal result in environmental contamination. Further, there is a risk of accidental leakage of nuclear radiation.
The high cost of installation of a nuclear power plant, high risk of environmental contamination and limited availability of uranium makes large-scale use of nuclear energy prohibitive.
Nuclear fusion
Currently all commercial nuclear reactors are based on nuclear fission.
But there is another possibility of nuclear energy generation by a safer process called nuclear fusion.
Fusion means joining lighter nuclei to make a heavier nucleus, most commonly hydrogen or hydrogen isotopes to create helium, such as 2 H + 2H → 3He (+ n)
It releases a tremendous amount of energy, according to the Einstein equation, as the mass of the product is little less than the sum of the masses of the original individual nuclei. Such nuclear fusion reactions are the source of energy in the Sun and other stars.
It takes considerable energy to force the nuclei to fuse.
The conditions needed for this process are extreme – millions of degrees of temperature and millions of pascals of pressure.
The hydrogen bomb is based on thermonuclear fusion reaction.
A nuclear bomb based on the fission of uranium or plutonium is placed at the core of the hydrogen bomb.
This nuclear bomb is embedded in a substance which contains deuterium and lithium.
When the nuclear bomb (based on fission) is detonated, the temperature of this substance is raised to 107 K in a few microseconds.
The high temperature generates sufficient energy for the light nuclei to fuse and a devastating amount of energy is released.
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