energy sources & it's types

                                             ENERGY RESOURCES

     

 CHARACTERISTICS OF ENERGY:

                            A source of energy should be such that it can provide an adequate amount of useful energy at a steady rate over a long period of time. It should be safe and convenient to use, economical and easy to store and transport.

CLASSIFICATION OF SOURCES OF ENERGY:

                            From the point of view of availability, the energy sources are divided into two groups. They are:

(1) renewable or non-conventional sources of energy, and

(2) non-renewable or conventional sources neither of energy.

RENEWABLE SOURCES OF ENERGY:

                         A natural source providing us energy continuously is called a renewable (or non- conventional) source of energy. Sun is the main source of energy for us on the earth. The energy harnessed from the natural sources like wind, flowing water, tides, ocean waves and biogas is directly or indirectly derived from the energy of the sun. We can use these sources as long as the earth continues to receive heat and light from the sun. Apart from these sources, geo- thermal energy and nuclear energy are the other sources of energy which can provide us energy over a long period of time.energy can be used again and again and will never get exhausted.

                          Although the wood, obtained from trees, is also considered a renewable source of energy. but trees usually take more than 15 years to grow fully, therefore, renewal of wood as source of energy takes a long time. Further, cutting of trees on a large scale causes depletion of forests which results in global warming and environmental imbalance. Hence use of wood as a source of energy must be avoided.

     

                              Thus, the main sources of renewable energy are: 

         (i) Sun 

         (ii) Wind 

         (iii) Flowing water (Hydro) 

         (iv) Bio mass and bio fuels from waste 

         (v) Tides 

         (vi) Oceans 

         (vii) Geo-thermal spots and 

         (viii) Nuclear fuel.

(i) Sun as source of energy: 

                Sun is the main source of various types of energy. The energy obtained from sun is called the solar energy. In the interior of the sun, nuclear fusion reactions generate huge amount of energy which is radiated out continuously in all directions in space. Since the sun is very far from the earth, we receive only a very small fraction of the total solar energy. 

                 The solar energy that reaches earth is neither uniform nor equal at all places. It changes daily even at one place. It also varies during a day. The average solar energy reaching the upper atmosphere of earth per second on an area of 1 metre2 is called the solar constant and it is estimated to be nearly 1-34 kW m². The solar energy reaching the earth is absorbed by land, plants and water bodies like rivers, lakes and oceans. The solar energy absorbed by land and water bodies cause winds, storms, rains, snow falls and sea waves, etc. while the solar energy absorbed by plants is utilized by them in preparing their food by the process of photosynthesis.

(ii) Wind as source of energy: 

                   The large mass of moving air is called wind. Due to motion, it has kinetic energy. The kinetic energy of wind is called the wind energy.

                   Indirectly wind energy comes from solar energy. The sun rays falling on earth heat different areas of earth unequally. Due to (i) unequal heating of different areas of earth, (ii) rotation of earth and (iii) local convection currents, we have different wind cycles.

                    From the very early days, we have been using energy possessed by wind for various purposes such as in removing husk from grains, in propelling sail boats in rivers and seas, in moving vehicles for transportation and in windmills to draw water from the ground and to grind grains.

(iii) Flowing water as a source of energy:

                    The kinetic energy possessed by the flowing water is called the hydro energy.Hydro energy too comes indirectly from the sun. The solar energy is responsible for water cycle in nature. Water in oceans, rivers, lakes, etc. absorbs solar energy and it then evaporates to form clouds. The clouds move due to air currents and ultimately water comes back on earth in the form of rain and snow.

                    Man has been utilizing for centuries the energy of flowing water in rivers for rotating the wheels of water mill used to drive the flour mill in remote hilly areas and for transporting heavy logs of wood from forests in hilly areas to the downstream areas in planes.

(iv) Bio mass as source of energy:

                     The wastes and dead parts of living beings like plants, trees and animals, is called bio mass. They contain carbon compounds. The chemical energy stored in the bio mass is called the bio energy. Thus, bio energy also comes from solar energy. Bio mass such as wood, cattle dung, crop residues and agriculture wastes like bagasse have been traditionally used as fuel to produce heat energy for domestic as well as commercial purposes.

                     Bio mass is also used to produce bio gas by its decomposition in the absence of oxygen. The main constituent of bio gas is methane (65%) and rest is a mixture of carbon dioxide, hydrogen and hydrogen sulphide. Bio gas is used as a fuel to run engines and for generating electricity. In India, we use two types of bio gas plants: 

(1) the floating gas holder type and 

(2) the fixed dome type. 

They are also called Gobar gas plants because the main bio mass used in these plants is called slurry which is the mixture of animal dung (or gobar) in water.

(v) Tides as source of energy: 

                 The rise of ocean water near the coast is called high tide and fall of ocean water is called low tide. This rise and fall of tidal waves occur twice a day in oceans. The energy possessed by rising and falling water in tides is known as tidal energy.

                 Tidal energy is harnessed for producing electricity by constructing a dam across a narrow opening to the sea. But this is not a major source of energy because of the following two reasons:

(1) The rise and fall of sea water during tides is not enough to generate electricity on a large scale.

(2) There are very few sites which are suitable for building the tidal dams.

(vi) Oceans as source of energy : 

                 Water in oceans possesses energy in two forms:

 (a) ocean thermal energy and 

(b) oceanic (or sea) waves energy.

Ocean thermal energy: 

              Water at the surface of an ocean gets heated by absorbing the heat of sun, while water at its deeper levels remains cold. Thus, there is a difference in temperature of water at the surface and at deeper levels of an ocean. This difference in temperature is found to be up to 20°C. The energy available due to the difference in temperature of water at the surface and at deeper levels of ocean is called the ocean thermal energy (OTE).

(b) Oceanic (or sea) waves energy: 

                 Due to the wind blowing on the surface of oceans, waves move at high speed on its surface which are called the oceanic waves (or sea waves). Due to their high speed, they carry tremendous amount of kinetic energy with them. Thus, the kinetic energy possessed by such fast moving oceanic (or sea) waves is called the oceanic (or sea) waves energy. This energy also comes indirectly from the sun.

                Sea waves energy can also be harnessed to produce electricity, but so far it has not become possible to produce electricity from sea waves energy on a large scale. However, models have been made to generate electricity from oceanic waves.

(vii) Geo thermal spots as source of energy: 

                At some places, rocks below the surface of earth are very hot. Such places are known as hot spots. The heat energy possessed by rocks inside the earth is called the geo thermal energy.

               Geo thermal energy is harnessed to produce electricity. The rocks present at hot spots, heat the underground water and turn it into steam, which gets compressed at high pressure between the rocks. By drilling holes into the earth up to the hot spots, steam is extracted through pipes which is utilized to rotate the turbine connected to the armature of an electric generator to produce electricity.

               In India, there are very few places where geothermal energy is harnessed to produce electricity. One such place is in Madhya Pradesh. However, in USA and Newzealand, there are a number of geo thermal energy based power plants.

(viii) Nuclear fuel as source of energy:

                When uranium nucleus is bombarded with a slow neutron, it splits into two nearly equal light nuclei and a large amount of energy is released. This phenomenon is called nuclear fission. Similarly, when two light nuclei combine to form a heavy nucleus at a very high temperature (≈ 107 K) and high pressure, a tremendous amount of energy is released. This phenomenon is called nuclear fusion. In both these processes, the origin of energy is the loss in mass i.e., the sum of masses of the products of reaction is less than the sum of masses of reactants and this loss in mass is converted into energy E according to the Einstein's mass- energy equivalence relation E = mc2, where c (=3 x 108 m s-1) is the speed of light and m is the loss in mass. This energy is known as nuclear energy.

                    In fission reaction of one uranium nucleus, nearly 200 MeV energy is released and two or three neutrons also emitted. If number of uranium nuclei present are more, each neutron emitted in the fission reaction of a uranium nucleus causes fission in the new uranium nuclei and thus a chain of nuclear fission reactions occurs, which once started continues till the entire uranium is exhausted. As a result of such an uncontrolled chain reaction, more and more energy is produced which may cause an explosion. An atom bomb is based on this principle. But to utilize the energy produced in the process of fission for constructive use (such as to produce electricity), the chain reaction is controlled by absorbing some neutrons with the help of cadmium rods. This is done in a nuclear reactor.So far it has not become possible to harness energy by the process of nuclear fusion.

NON-RENEWABLE SOURCES OF ENERGY:

                     The sources of energy which have accumulated in nature over a very long period and cannot be quickly replaced when exhausted, are called the non-renewable or conventional sources of energy. Coal, petroleum and natural gas known as fossil fuels are non-renewable sources. They are formed by the decomposition of the remains of plants and animals buried under the earth, millions of years ago. Thus, the formation of fossil fuels have occurred over millions of years due to certain very slow changes under special circumstances. If they are being used extensively, their known reserves will soon deplete and once exhausted, they cannot be regenerated soon.

    

                     The common non-renewable sources of energy are: 

         (i) coal, 

         (ii) petroleum and 

         (iii) natural gas.

(1) Coal: 

          Coal is a non-renewable source of energy made up of complex compounds of carbon. hydrogen and oxygen along with some free carbon and compounds of nitrogen and sulphur. It is found in deep mines under the surface of earth. In India, coal mines are found in Jharkhand, West Bengal. Orissa and Chhattisgarh. Since coal is found in abundance in our country, it is the most common source of energy for us.

(ii) Petroleum: 

           Petroleum is a dark colored viscous liquid also called crude oil. It is a non-renewable source of energy which is found under the earth's crust trapped in rocks. It is called petroleum because petroleum means rock oil. It is a complex mixture of many hydrocarbons with water, salt, earth particles and other compounds of carbon, oxygen, nitrogen and sulphur. It is lighter than water and does not mix with it. Petroleum is obtained by drilling oil wells into the earth's crust at its reservoirs. In India, the reservoirs of petroleum have been in Assam and Mumbai.

             The crude petroleum extracted from wells is not suitable to be used as a fuel in its natural form. It has to be purified (or refined) to obtain different useful components. The process of separating useful components from crude petroleum is called refining which is done by fractional distillation in big oil refineries set up for this purpose.

             The petroleum gas obtained as a by-product from the fractional distillation of petroleum contains mainly the butane and a small amount of propane and ethane. These gases burn readily and produce a lot of heat. Hence the petroleum gas can be used as a good fuel.

              Butane, propane and ethane are in gaseous states at ordinary pressure, but they can be easily liquefied under pressure. The petroleum gas liquefied under pressure is called the liquefied petroleum gas (or LPG) which is used in domestic gas stoves as fuel for heating purposes. It is stored in gas cylinders after mixing a strong smelling substance called ethyl mercaptan (C,H,SH) so that the gas leakage, if any, from the cylinder can easily be detected.

(iii) Natural gas: 

Natural gas is also a non-renewable source of energy which is found deep under the earth's crust either alone or above the petroleum reservoirs. It is also obtained by digging wells into the earth. From some wells we can extract only the natural gas, while from others both the natural gas and petroleum. In India, there are a number of natural gas fields such as in Tripura, Jaisalmer, off shore area of Mumbai and in the Krishna- Godavari delta. The main component of natural gas is methane (up to 95%) along with small quantities of ethane and propane. It easily burns to produce heat.