Chapter-14
Source of Energy
• Energy comes in different forms and one form can be converted into another.
• A source of energy is one which provide adequate amount of energy in a covenient form over a long period of time.
Need of Eenergy:
• For Making Food
• For Lighting
• For Transport
• For Running Machines
• For Industrial Activities and Agricultural Work
Qualities of a Good Source of Energy
(i) Which would do a large amount of work per unit mass.
(ii) Cheap and easily available.
(iii) Easy to store and transport.
(iv) Safe to handle and use.
(v) Does not cause environmental pollution.
Fules : The materials which ar burnt to produce heat energy are known as fuels. E.g., Wood, Coal, LPG, Kerosene.
Characteristics of a Good Fuel
• High calorific value (give more heat per unit mass).
• Burn without giving out any smoke or harmful gases.
• Proper ignition temperature.
• Cheap and easily available.
• Easy to handle, safe to transport.
• Convenient to store.
• Burn smoothly.
| Conventional Sources of Energy | Non-conventional Sources of Energy |
|---|---|
| • Fossil fuels (Coal, Petroleum) | • Solar energy (e.g., solar cooker, solar cell panel) |
| • Thermal Power Plant | • Energy from the sea (tidal wave, OT energy) |
| • Hydro power plants | • Biomass-biogas plant • Wind energy |
| • Geothermal energy | • Nuclear energy |
CONVENTIONAL SOURCES OF ENERGY
Sources of energy which are known to most of the people. E.g., fossil fules, biomass etc.
I. FOSSILL FUELS:
• Fuels developed from the fossils e.g., coal, petroleum.
• Take millions of years to form.
• Available in very limited amount.
• These are non-renewable sources of energy.
India has about 6% share in the world reserved coal, that may last 250 years more at the present rate of consumption.
Pollution Caused by Fossil Fuels
• Released oxides of carbon, nitrogen and sulphur (acidic in nature) which causes acid rain that damages trees, plants, reduces fertility of soil.
• Produces large amount of CO2 the atmosphere which causes green house effect leading to excessive heating of the earth.
Controlling Pollution Caused by Fossil Fuels
• Increasing the efficiency of the combustion process.
• Using various techniques to reduce the escape of harmful gases and ashes into the surroundings.
II. THERMAL POWER PLANT:
A power plant which uses heat energy to generate electricity.
• Burning of fossil fuels produces steam to run turbines.
• Set up (power plants) near the coal and oil fields to minimize the cost of transportion and production.
• Transmission of electricity is more efficient.
III. HYDRO POWER PLANTS :
• Convert the potential energy of falling water into electricity.
• Hydro power plant are associated with Dams.
Around 25% of our conutry's energy requirement is met by Hydro Power Plants.
Advantages :
(i) No environmental pollution.
(ii) Flowing water is a renewable source of elctric energy.
(iii) Construction of dams prevents floodings of rivers, provide water for irrigation.
Disadvantages :
| (i) Large areas of agricultural land, a vast variety of flora and fauna, human settlements get submerged in the water of reservoir formed by the dam. |
| (ii) Large ecosystems are destroyed. |
| (iii) Vegetation that submerged under water rots under anaerobic conditions and produces large amount of methane which is a green house gas. |
| (iv) Creates the problems of satisfactory rehabilitation of diplaced people. |
Improvement in the Technology for Using
Source of Energy
I. BIOMASS :
The dead parts of plants and trees and teh waste materials of animals and man are called Biomass.
(1) Wood : It is a biomass and used as a fuel for a long time.
Disadvantages :
• Produces a lot of smoke on burning.
• Do not produce much heat.
• Thus by imporvement in technology we can improve the efficiency of traditional sources of energy.
For e.g., wood can be converted into much better fuel called charcoal.
(2) Charcoal : When wood is burnt in limited supply of air, then water and other volatile materials gets removed and charcoal is formed.
Wood ----Limited Supply of O2-→ Charcoal
Charcoal is better fuel than wood because:
(i) It has higher calorific value than wood.
(ii) Does not produce smoke while burning.
(iii) It is a compact fuel, easy to handle and convenient to use.
(3) Cowdung : It is biomass but it is not good to burn cowdung directly as fuel because:
• Produces lot of smoke.
• Cowdung does not burn completely, produces lot of ash as residue.
• low calorific value.
• by making bio gas (or gobar gas) from cow dung, we get a smokeless fuel.
(4) Bio gas : It is produced in a biogas plant. Anaerobic micro organisms decomposes the complex compund of the cow dung + water slurry. It takes few day for the decomosition process and generate gases like methane, CO2, hydrogen and hydrogen sulphide. Bio gas is stored in the gas tank above teh digester from which they are drawn through pipes for use.
Advantages of Bio gas:
| (i) It is an excellent fuel as it contains upto 75% methane (CH4). |
| (ii) It burns without smoke. |
| (iii) Leaves no residue like ash in wood & coal burning. |
| (iv) Heating capacity is high. |
| (v) It is also used for lighting. |
| (vi) Slurry left behind is used as excellent manure rich in nitrogen and phosphorus. |
| (vii) Safe and efficient method of waste disposal. |
(5) Wind energy :
• Unequal heating of the landmass and water bodies by solar radiations generate air movement and causes wind to below.
• Kinetic energy of the wind can be used :
* to generate electricity by turning the rotor of the turbine.
* to lift water from the well.
* to run the flour mills.
• But the output of a single wind mill is quite small so a number of windmills are erected over a large area called wind energy farm.
• The minimum wind speed for wind mill to serve as a source of energy is 15-20 KmPH.
Advantages :
| (i) Eco-friendly. |
| (ii) Efficient |
| (iii) No recurring expenses for production of electricity. |
Disadvantages :
| (i) Wind energy farms need large area of land. |
| (ii) Difficulty in getting regular wind speed of 15-20 KmPH. |
| (iii) Initial cost of establishing wind energy farm is very high. |
| (iv) High level of maintenance of blades of wind mill. |
• Demark is called is the 'Country of Winds'.
• India is ranked 5th in harnessing wind energy for the Production of electricity.
• In India largest wind energy farm has been established near Kanyakumari in Tamil Nadu and it generates 380 MW of electricity.
Alternate or Non-convential Sources of Energy
Day by day, our demand for energy increases, so there is a need for another source of energy.
Reasons for alternate sources of energy
| (i) The fossil fuel reserve in the earth are limited which may get exhausted soon if we use them at the current rate. |
| (ii) Reduce the pressure on fossil fules making them last for a much longer time. |
| (iii) To reduce the pollution level and to save the environment. |
I. SOLAR ENERGY :
• Sun is the ultimate source of energy.
• Energy obtained form the sun is called solar energy.
Solar constant = 1.4 KJ/s/M2
Outer edge of the earth receives solar energy equal to 1.4 KJ/s/m2 or 1.4 KW/m2 [... 1 KJ/s = 1 KW]
Solar Energy Devices : Devices using solar energy are :
(i) Solar cooker
(ii) Solar water heater
(iii) Solar cells
Solar Heating Devices :
• Use black painted surface becuase black surface absorbs more heat as compared to white or other surface.
• Use of glass plate becuase it allows infrared radiations to enter through it but does not allow the readiations to exit through it, causing more green house effect that result in increases in temperature.
(i) SOLAR COOKER
Box Type of Solar Cooker : It consists of a rectangular box which is made up of wood or plastic which is painted dull back.
• Inner walls of the box are painted black to increase heat absorpation.
• Solar cookers are covered with glass plate and have mirror to foucs the rays of the sun and achieve higher temperature.
• Temperature inside the box increases 100oC-140oC in 2-3 hours.
Advantages :
| (a) Save precious fuel like coal, LPG, kersoene. |
| (b) Does not produce smoke. |
| (c) Nutrientsn of food do not get destroyed while cooking. |
| (d) Upto four food items can be cooked at the same time. |
Disadvantages :
| (a) Solar cookers cannot be used during night. |
| (b) If the day sky is covered with clouds, even the solar cooker cannot be used. |
| (c) Direction of reflector of solar cooker changes form time to time to keep it facing the sun. |
| (d) Cannot be used for frying or baking purpose. |
II. SOLAR CELL :
• Solar cells convert solar energy into electricity.
• A solar cell develops a voltage of 0.5-1 V and can produce about 0.7 W of electricity.
• A large number of solar cell are combined in an arrangement called solar cell panel.
Advantages :
| (a) Have no moving parts. |
| (b) Require little maintenance. |
| (c) Can work without any focusing device. |
| (d) Can be set up in remote and inacessible areas. |
Disadvantages :
| (a) Maufacturing is expesive. |
| (b) Availability of special grade silicon for making solar cells is limited. |
| (c) Silver wire for interconnection of cells is expensive. |
Uses of Solar Cell :
| (a) Aritifical satellites and space probes use solar cells as the main source of energy. |
| (b) Radio, TV relay stations in remote locations use solar cell panels. |
| (c) Traffic signals, calculators and many toys are fitted with solar cells. |
III. ENERGY FROM THE SEA
| Tidal Energy | Wave Energy | Ocean Thermal Energy | |
|---|---|---|---|
| Working: | (i) The phenomenon of high and low tide give us tidal energy. | Kinetic energy of huge waves near sea shore is trapped to generate electricity. | The difference in the temperature of water at the surface and deeper section of ocean is used to obtain energy inn ocean thermal energy conversion plants. (OTEC) |
| (ii) It is harnessed by constructing a dam across the narrow opening of hte sea. | Wave energy is used for rotation of turbine and production of electricity. | The warm surface water is used to boil volatile liquid ammonia. The vapours of the liquid are used to run the turbine of generator to produce electricity. | |
| Disadvantages: | The locations where such dams can be built are limited. | Wave energy is viable energy is viable only where waves are very strong. | Efficient commercial exploitation is very diffciult. |
GEOTHERMAL ENERGY
• 'Geo' means 'earth' and 'thermal' means 'heat'.
• Geothermal energy is the heat energy from hot rocks present inside the earth.
• When underground water comes in contact with 'hot spot', steam is generated. Steam trapped in rocks is routed through pipes to turbine and used to generate electricity.
Advantages:
(a) Economical to use geothermal energy.
(b) Does not causes any pollution.
Limitations:
(a) Geothermal energy is not available everywhere.
(b) Deep drilling in the earth to obtain geothermal energy is very diffciult and expensive.
• In New Zealand and USA, there are no. of power plants based on geothermal energy are opertional.
NUCLEAR ENERGY
• The energy released during a nuclear reaction is called nuclear energy.
• In can be obtained by two types of nuclear reactions :
(i) Nuclear fission
(ii) Nuclear fusion
(i) Nuclear Fission:
| • 'Fission' means split up. |
| • The process in which the heavy nucleus of a radio active atom (such as uranium, plutonium or thorium) split up into smaller nuclei when bombarded with low energy is produced. |
| • A tremedoous amount of energy is produced. |
| • U-235 is used as a fuel in nuclear reactor in form of uranium rods. |
Working : In a nuclear reactor self sustaining chain reaction releases energy at a controlled rate, which is used to produce steam and further generate electricity.
Major Nuclear Power Plants :
| (a) Tarapur (Maharashtra) |
| (b) Rana Pratap Sagar (Rajasthan) |
| (c) Kalpakkam (Tamil Nadu) |
| (d) Narora (U.P.) |
| (e) Kakrapar (Gujrat) |
| (f) Kaiga (Karnataka) |
(ii) Nuclear Fusion:
When two nuclei of light elements (like hydrogen) combine to form a heavy nucleus (like helium) and tremendous amount of energy is released is called nuclear fusion.
2 H (deuterium) + 2 H fusion 3 He + 1n + Heat 1 1 2 0
• Very-very high temperature and pressure is needed for fusion.
• Hydrogen bomb is based on this phenomenon.
• Nuclear fusion is the source of energy in the sun and other stars.
Advantages:
| (a) Production of large amount of useful energy form a very small amount of nuclear fuel. |
| (b) Does not produce green house gases like CO2. |
Limitations:
| (a) Environmental contamination due to improper nuclear waste storage and its disposal. |
| (b) Risk of accidental lekage of harmful radiations. |
| (c) High cost of installation. |
| (d) Limited availability of nuclear fuel. |
Environmental Consequences
Exploiting any source of energy distrubs the environment in some way to the other. Thus, the source we would choose depends upon following the factors :
| (a) Ease of extracting energy from the source. |
| (a) Cost of extracting energy from the source. |
| (c) Efficiency of technology available to extract energy. |
| (d) The environmental damage caused by using that source. |
In other words, no source of energy is said to be pollution free. Some source are cleaner than the other.
For example, solar cells may be pollution free but the assembly of the device would have cause some environmental damage.
How long will an energy resource last us ?
| ↓ Renewable Sources of Energy |
↓ Renewable Sources of Energy |
|---|---|
| Sources that will get depleted some day. For example : Fossil fuel |
Energy sources that can be regenerated and that will last for ever. For example : Wind energy, water energy. |
