Sources Of Energy
Good Sources of Energy
A good source of energy would be one :
1. Which would do a large amount of work per unit volume or mass.
2. Be easily accessible
3. Be easy to store and transport.
4. The source of energy has to be economical.
Classification of Sources of Energy
We can classify energy sources in different ways. One classification is based on the reserves (supply) of an energy source. Another is based on how long we have been using it.
Renewable and nonrenewable sources of energy:
Renewable sources of energy are those which can be generated by us or which are constantly being generated by natural processes or whose supply is unlimited.
Nonrenewable sources of energy are those which were produced in the past by natural processes, whose supply is limited and which we cannot generate ourselves.
Coal, natural gas and petroleum are nonrenewable sources of energy. Wood is a renewable source of energy although its supply is limited. But if we replant and use trees in a planned manner, we can be assured of a continuous supply of firewood. The sun, wind and flowing water are also renewable sources because of their unlimited availability. Unlike fuels like coal, nuclear fuels such as uranium are required in very small quantities to generate electricity. So, their reserves will last for a long, long time. They are therefore classified as renewable sources of energy.
Conventional and nonconventional sources of energy
Sources of energy that have been in use for centuries are called conventional sources of energy. Conventional sources include wood, coal, petroleum and flowing water. Conventional sources like coal and petroleum are nonrenewable, while sources like flowing water are renewable.
Sources of energy that we have started using in new ways or only in recent times are called nonconventional or alternate sources of energy. These include energy from the sun, the heat inside the earth (geothermal energy), tides, ocean waves, etc. Nuclear energy is also a nonconventional source. Note that nonconventional energy sources are renewable.
We have been using wind and biomass (like cow dung) for energy for ages. In that sense they are conventional sources. However, they were not used conventionally to do tasks like electricity generation, which has now been made possible with improvement in technology. In that sense they can also be called nonconventional sources of energy.
Fuels that were formed from the remains of dead plants and animals are called fossil fuels. These were produced by complex processes with the help of a series of natural events over millions of years. The most widely used fossil fuels are coal, petroleum and natural gas. Plants trap solar energy in the form of food, and animals get energy when they eat the plants. Since fossil fuels came from plants and animals, their ultimate source of energy is the sun.
We get a number of different fuels from coal and petroleum. For example, we get petrol, diesel, kerosene and LPG from petroleum, and coke and natural gas from coal. When burnt in air, fossil fuels give off heat, which is used for various purposes-from cooking to generating electricity. However, these fuels are nonrenewable, and their reserves are running out. Unfortunately, we cannot repeat the events that led to their formation.
Fossil fuels have played an important role in the technological advances made in the last three hundred years or so. Even today, most of the energy requirements of homes, industries and transport are met by fossil fuels. It is estimated that about 25% of our total energy consumption comes from coal. More than 90% of this coal is used for electricity generation in thermal power plants.
In most thermal power plants, coal is burnt to heat water for producing steam. The steam falls on the blades of a special kind of wheel called a turbine. A turbine is a device that rotates when steam, water or wind falls on its blades. The turbine turns the shaft of an electric generator to which it is connected. In this way electricity is produced.
Thermal power plants generated 65.6% of the total electricity produced in India in 2006. The rest was generated by hydroelectric (26.6%), nuclear (3%) and renewable-energy (4.8%) power plants.
In some thermal power plants, natural gas or oil is used as fuel. Natural gas is mainly methane (CH4). It is the cleanest fossil fuel, producing lesser pollutants than other fossil fuels. That is why vehicles using compressed natural gas (CNG) cause less pollution.
Pollution Caused by Burning Fossil Fuels
The burning of most fossil fuels causes air pollution. The pollutants produced include carbon dioxide, carbon monoxide, oxides of nitrogen, sulphur dioxide and unburnt particles.
(a) Burning of fossil fuels like coal and petrol produces carbon dioxide. Excess carbon dioxide' in the atmosphere is increasing the greenhouse effect, leading to unnatural global warming.
(b) When coal and petrol do not burn completely, carbon monoxide is produced. Excessive inhalation of this poisonous gas can cause death.
(c) During the combustion of coal, sulphur present in it forms sulphur dioxide. Oxides of nitrogen are formed when atmospheric nitrogen and oxygen combine at the high temperatures inside a running automobile engine. In the air, sulphur dioxide combines with oxygen and water to form sulphuric acid. Oxides of nitrogen form nitric acid. These fall on the earth with rain, which we call acid rain. Acid rain damages soil, water bodies, crops, living tissues and structures like the Taj Mahal.
(d) The unburnt particles produced during the combustion of fossil fuels are carried by smoke.
They affect our lungs, and blacken clothes and buildings. The pollution caused by burning coal can be greatly reduced by installing a tall chimney or by installing a precipitator, which is a device that reduces the amount of suspended matter in the smoke.
ENERGY FROM FLOWING WATER: HYDRO ENERGY
When we talk of flowing water, we think of water flowing in rivers, streams, waterfalls, and so on. The flowing water has kinetic energy. The ultimate source of this energy is the sun. This is because the energy of the sun evaporates water, which forms clouds that cause rainfall or snowfall. The rain and melting snow feed rivers, etc., whose flow we use.
The energy of flowing water has been used for centuries to carry logs down rivers, to turn waterwheels to grind grain, run mills, and so on. Water striking the blades of the waterwheel makes it rotate. This design was modified to make water turbines, which are used to generate electricity from flowing water.
Electricity generated by using the kinetic energy of flowing water is called hydroelectricity. The electric power thus generated is called hydroelectric power.
Electricity is generated from flowing water at a hydroelectric power plant. For large hydroelectric plants, water from a river is diverted to a large reservoir, which is an artificial lake to store water. A high dam is constructed on one side of the reservoir to hold back the water. The building housing the generator is at the base of the dam, on its other side. Water flows down through pipes from near the top of the dam to the generator house below. It strikes the blades of a water turbine with tremendous speed, making it rotate. The turbine rotates the shaft of a generator to which it is connected. This makes the generator produce electricity. In this way, the kinetic energy of flowing water is used to rotate the turbine, and the rotational kinetic energy is converted into electrical energy.
It is not necessary to set up large dams for hydroelectric plants. Small hydroelectric plants can be set up to generate electricity from a few hundred kilowatts to tens of megawatts. Such plants can use water diverted from a waterfall or from a dam built for irrigation.
Advantages of hydroelectricity
(a) The source of energy (water) is free and renewable.
(b) Harnessing the energy of flowing water is a pollution-free process, with no smoke, chemicals, etc., being produced.
(c) The cost of electricity generation is low as compared to electricity generated from other types of power plants.
(d) Flowing water is a more reliable source of energy than wind.
(e) Hydroelectricity can be generated on a large scale from a single plant.
(f) Dams built for hydroelectric plants also help in flood control and irrigation.
(g) Small hydroelectric stations are one of the best options for generating electricity from renewable sources, as they do not affect the environment much.
Disadvantages of hydroelectricity
(a) Dams built for large hydroelectric plants submerge a large area of land under water. This affects the plants and animals of the region. People of the area lose their lands. Apart from this, blocking or changing the course of a river affects fish and other organisms of the river.
(b) Large hydroelectric power plants are expensive to build.
(c) Not all rivers and not all areas are suitable for hydroelectric power generation.
Scope of hydroelectricity
Hydroelectricity has huge potential worldwide. In India, it is estimated that 145,000 MW of hydroelectricity can be generated. Out of this, by 2006, India had an installed capacity of about 34,000MW.
A moving mass of air is called wind. Let us see, with the help of an example, what causes wind. During the day, the land near the sea heats up faster than the water of the sea. Therefore, the air over the land heats up faster than that over the sea. The warm air over the land rises, and to take its place the colder air from the sea moves towards the land. This moving air is called wind. Similarly, winds arise whenever two adjoining areas on the surface of the earth are unequally heated by the sun. Like any moving object, wind has kinetic energy. Clearly, the ultimate source of this energy is the sun.
The invention of the windmill made it possible to do things like grind grain at mills and lift water with the help of wind energy. A windmill is a device in which the energy of the wind is used to rotate a set of blades, and the rational energy of the blades is used to do some work. The blades of a modem windmill make it look like a fan mounted on a tall column. The blades are kept high above the ground to catch the wind.
Generating Electricity from Wind
A windmill can be designed to rotate the shaft of a generator. Such a windmill is usually called a wind turbine.
A specially designed wind turbine is connected to the shaft of small generator. The electricity produced by such an arrangement is not sufficient even for a small town. To be commercially useful, a number of wind-electric generators are set up in a large area, called a wind farm. The combined electrical outputs of all the generators are then used to supply power.
Advantages of wind energy
(a) The source of energy (wind) is free.
(b) Harnessing wind energy is a pollution-free process, with no smoke, chemicals, etc., being produced.
(c) A small wind-electric plant can be set up near a factory to provide pollution-free power for its use.
Limitations of wind energy
(a) Wind energy cannot be harnessed at places where wind does not blow regularly. A wind-electric generator works only on winds of at least 15 km/h.
(b) Wind is not a dependable source of energy because sometimes the air is absolutely still and at other times there are storms.
(c) It is expensive to set up a wind farm for generating electricity because wind farms need a large area.
Scope of wind energy
It is estimated that India can produce more than 45,000 MW of electricity from wind energy. By 2005, India had an installed wind-electric capacity of about 2500 MW. This made India among the top five producers of electricity from wind along with Germany, USA, Denmark and Spain. The state leading in wind-electric generation was Tamil Nadu.