SOURCES OF ENERGY
Sources of Energy
We have a wide range of sources of energy such as the sun, the wind, the earth (geothermal), flowing water, coal, gasoline, diesel, natural gas, biogas, etc. at our disposal. We utilize this energy to perform a wide range of activities, i.e. industrial, commercial, household etc. A source of energy is one which can provide adequate amount of energy in a convenient form over a long period of time.
CLASSIFICATION OF SOURCES OF ENERGY
1. Renewable and nonrenewable sources of energy:
(A) Renewable Sources of Earth
Those sources of energy which are being produced continuously in nature and are inexhaustible, are called renewable sources of energy. Example: wood is a renewable source of energy because if trees are cut from the forests for obtaining wood then more trees will grow in the forest in due course of time.
The renewable sources of energy are:
Examples: Hydroenergy (Energy from flowing water) ; Wind energy ; Solar energy ; Energy from sea (Tidal energy); Sea wave energy and Ocean thermal energy) ; Geothermal energy ; Biomass energy (Energy from bio fuels such as Wood, Bio gas and Alcohol) ; and Hydrogen
(B) Non- Renewable Sources of Energy
Those sources of energy which have accumulated in nature over a very, very long time and cannot be quickly replaced when exhausted are called non – renewable sources of energy.
Example: coal is a non – renewable source of energy because coal has accumulated in the earth over a very, very long time and if all the coal gets exhausted, it cannot be produced quickly in nature.
The non renewable sources of energy are
Examples: Fossil fuels (Coal, Petroleum and natural gas) and Nuclear fuels (such as uranium). Non – renewable sources of energy are dug out from the earth.
2. CONVENTIONAL AND NONCONVENTIONAL SOURCES OF ENERGY:
(A) CONVENTIONAL SOURCES OF ENERGY
The traditional sources of energy which are familiar to most people are called conventional sources of energy. The main conventional sources of energy are wood and fossil fuels (like coal, petroleum and natural gas). The fuels derived from wood, coal and petroleum such as charcoal, coke, coal gas, petrol, diesel, kerosene, fuel oil and liquefied petroleum gas (LPG) are also known as conventional sources of energy.
(B) Non-conventional sources of energy
Sources of Energy that we have started using in New ways or Only in Recent times are called alternative sources of energy (or non conventional sources of energy).
Examples: Hydroelectric energy, Wind energy, Solar energy, Biomass energy, Energy from the sea (Tidal energy, Sea – wave energy, Ocean thermal energy), and Geothermal energy.
A fuel is a chemical which releases energy when heated with oxygen. The energy may release in the form of heat and light. ‘
Examples: Wood, gas, petrol, kerosene, diesel, coal and animal waste.
Note: Fuels are combustible substances.
(a) Characteristics of a good fuel
(i) It should have high calorific value.
(ii) It should have a proper ignition temperature so that it may burn easily.
(iii) It should leave no residue (or very small amount of residue) or ash after burning.
(iv) It should burn smoothly i.e. it should have a moderate rate of combustion and burn at a steady rate.
(v) It should not be more valuable for some other purpose than fuel. For e.g. coke is a good fuel but it is more valuable as a reducing agent in the extraction of metals.
(vi) It should be cheap and easily available.
(vii) It should be easy to handle, safe to transport and convenient to store.
(b) Types of Fuels
There arc three types of fuels solid fuels, liquid fuels and gaseous fuels.
(i) Solid fuels: The various kinds of solid fuels are wood, charcoal, coke, coal, paraffin and tallow. Wood was the first solid fuel to be used by humans. Paraffin and tallow are used to make candles.
(ii) Liquid fuels: Petrol, kerosene, diesel and methanol are some common liquid fuels. Most of the liquid fuels arc obtained from petroleum. They leave no solid residue when burnt and can be stored easily.
(iii) Gaseous fuels: Natural gas, coal gas, producer gas, water gas and liquefied petroleum gas are some examples of gaseous fuels.
(c) Fossil Fuels: Fossil fuels are the remains of the prehistoric animals or plants, burried under the earth, millions of years ago. Eg. Coal, petroleum and natural gas. Fossil fuels are formed in the absence of oxygen. The chemical effects of pressure, heat and bacteria convert the burried remains of plants and animals into fossil fuels like coal, petroleum and natural gas. It was the sunlight of long ago that made plants grow, which were then converted into fossil fuels. Fossil fuels are energy rich compounds of carbon, which were originally made by the plants with the help of sun’s energy.
(d) Calorific value of fuels: All the fuels produce heat energy on burning. Different fuels produce different amount of heat on burning. The usefulness of a fuel is measured in terms of its calorific value. The amount of heat produced by burning a unit mass of the fuel completely is known as its calorific value. The unit of mass usually taken for measuring the calorific value of a fuel is gram So it can be said that the amount of heat produced by burning 1 gram of a fuel completely is called its calorific value. For example, when one gram of a carbon fuel (like charcoal) is burned completely, it produces 33000 joules of heat. So the calorific value of charcoal is 33000 Joules per gram or 33000 J/gm. Since joule is a very small unit of heat energy so the calorific value is usually expressed as kilojoules per gram (KJ/g). The SI unit of measuring calorific value is kilojoules per gram.
Of all the common elements. hydrogen has the higher calorific value. So a fuel containing percentage of hydrogen will have a higher calorific value than another fuel which has a lower percentage of hydrogen in it.Of all the common elements. hydrogen has the higher calorific value. So a fuel containing percentage of hydrogen will have a higher calorific value than another fuel which has a lower percentage of hydrogen in it. Wood is a mixture of carbon compounds called carbohydrates like cellulose (C6H10O5)n. Thus, when wood is burnt, only carbon and hydrogen atoms contained in it burn and produce heat. Oxygen atoms do not produce any heat, they only help in the burning process. So due to comparatively lower percentage of carbon and hydrogen in wood, it has a low calorific value. All the fuels which contain oxygen burn ready but produce less heat energy per unit weight. The calorific value of some common fuels are given in the table below. The material which are burnt to produce heat energy are known as fuels.
Examples of fuels are: Wood, Coal, Cooking gas (LPG), Kerosene, Diesel and Petrol.
The amount of heat produced by burning a unit mass of the fuel completely is known as its calorific value. The unit of mass usually taken for measuring the calorific value of a fuel is gram For example : when one gram of a carbon fuel (like charcoal) is burned completely, it produced about 33000 joules of heat, so the calorific value of charcoal is 33000 joules per gram or 33000 J/g. The common unit of measuring calorific value is kilojoules per gram (kJ/g.).
Calorific Values (or Heat values) of some common fuels
Hydrogen gas has the highest calorific value of 150 kilojoules per gram. Thus, because of its high calorific value, hydrogen is an extremely good fuel.
The minimum temperature to which a fuel must be heated so that it may catch fire and start burning is known as its ignition temperature.
A natural fuel formed deep under the earth from the pre-historic remains of living organisms (like plants and animals) is called a fossil fuel. Coal, petroleum and natural gas are fossil fuels. Fossil fuels are the major source of energy for generating electricity in power plants.
- How Fossil Fuels were formed?
The plants and animals which died millions of years ago, were gradually buried deep in the earth and got covered with sediments like mud and sand, away from the reach of oxygen of air. In the absence of oxygen, the chemical effects of pressure, heat and bacteria, converted the buried remains of plants and animals into fossil fuels like coal, petroleum and natural gas.
Coal is a complex mixture of compounds of carbon, hydrogen and oxygen, and some free carbon. Small amounts of nitrogen and sulphur compounds are also present in coal. A lot of heat is produced during the burning of coal which makes it a good fuel. Coke is a better fuel than coal because it produces more heat (than an equal mass of coal), and it does not produce smoke while burning.
- Uses of Coal
(i) Coal is used as a fuel for heating purposes in homes and in industry. (ii) Coal is used as a fuel in thermal power plants for generating electricity. (iii) Coal is used to make coke. (iv) Coal is used in the manufacture of fuel gases like coal gas. (v) Coal is used in the manufacture of petrol and synthetic natural gas.
Petroleum is a dark coloured, viscous, and foul smelling crude oil.
The name petroleum means rock oil.
It is called petroleum because it is found under the crust of earth trapped in rocks. The crude oil petroleum is a complex mixture of several solid, liquid and gaseous hydrocarbons mixed with water, salt and earth particles.
Petroleum is the crude oil which is a complex mixture of alkane hydrocarbons with water, salt and earth particles. Petroleum cannot be used as a fuel as such.
The fractional distillation of petroleum gives us the following fractions which can be used as
fuels: Petroleum gas, Petrol (or Gasoline), Diesel, Kerosene and Fuel oil. Petroleum gas is used as a fuel for domestic heating purposes in the form of liquefied petroleum gas. Petrol is used as a fuel in motor car, scooters, motor cycles and other light vehicles. Diesel is used as a fuel for heavy vehicles like buses, trucks, tractors and railway engine. Kerosene oil is used as a household fuel. Fuel oil is a better fuel than coal because fuel oil burns completely and does not leave any residue.
3. Petroleum Gas (LPG)
The main constituent of petroleum gas is butane though it also contains smaller amounts of propane and ethane. Petroleum gas is obtained as a by product in oil refineries from the fractional distillation of petroleum. The petroleum gas which has been liquefied under pressure is called Liquefied petroleum (LPG), Thus, liquefied petroleum gas (or LPG) consists mainly of butane (along with smaller amounts of propane and ethane), which has been liquefied by applying pressure. In other words, the domestic gas cylinders like Indane contain mainly butane. A domestic gas cylinder contains about 14 kilograms of LPG. A strong smelling substance called ethyl mercaptan (C2H5SH) is added to LPG cylinders to help in the detection of gas leakage.
- Advantages of LPG
(i) LPG has a high calorific value, So it is a good fuel. (ii) LPG burns with a smokeless flame and so does not cause air pollution. (iii) LPG does not produce any poisonous gases on burning. (iv) LPG is easy to handle and convenient to store. (v) LPG is a very neat and clean domestic fuel.
- Dangers of LPG
LPG is a highly inflammable gas, that is, it catches fire easily. Any leakage of LPG from the gas cylinder, stove or the rubber pipe will form an explosive mixture with air in the kitchen. And on lighting the match stick, an explosion will take place, the whole kitchen will be set on fire and the person working in the kitchen may get burnt.
- Percautions of Using LPG
(i) Before lighting a match stick we should make sure that there is no foul smell of the leaking gas in the kitchen, near the gas cylinder or gas stove.
(ii) We should not use any hot flames like a kerosene lamp, kerosene stove or electric heater near the gas cylinder.
(iii) We should never use a leaking gas cylinder.
(iv) We should handle the gas cylinder with care so that its valve does not get damaged.
(v) The rubber pipe connecting the gas cylinder to gas stove should be checked periodically for any wear and tear.
4. Natural Gas
Natural gas consists mainly of methane (CH4) with small quantities of ethane and propane. In fact, natural gas contains upto 95% methane, the remaining being ethane and propane. Natural gas occurs deep under the crust of the earth either alone or alongwith oil above the petroleum deposits. Natural gas is formed under the earth by the decomposition of vegetable matter lying under water. This decomposition is carried out by anaerobic bacteria.
1. Natural gas is used as a domestic and industrial fuel.
2. Natural gas is used as a fuel in thermal power plants for generating electricity.
3. Compressed Natural gas (CNG) is being used increasingly as a fuel in transport vehicles.
- Advantags of Natural gas
(i) Natural gas being a complete fuel in itself can be used directly for heating purposes in homes and industries.
(ii) Natural gas is a good fuel because it has a high calorific value of about 50 kJ/g.
(iii) A great advantage of natural gas is that it can be supplied directly from the gas wells to the homes and factories for burning through a net – work underground pipelines, and this eliminates the need for additional storage and transport.
- Pollution Caused by Fossil Fuels
(i) The burning of fossil fuels produces acidic gases such as sulphur dioxide and nitrogen oxides.
(ii) The burning of fossil fuels produces large amount of carbon dioxide which goes into air.
(iii) The burning of fossil fuels (especially coal) produces smoke which pollutes the air.
(iv) The burning of coal leaves behind a lot of ash.
- Controlling Pollution Caused by Fossil Fuels
(i) The pollution of air caused by burning petroleum fuels (like petrol and diesel). in vehicles can be controlled by fitting the vehicles with catalytic converters.
(ii) The pollution of air caused by burning coal in thermal power plants and factories can be controlled by washing down the smoke and acidic gases by water in a scrubber.
(iii) The pollution of air caused by burning coal in thermal power plants and factories can also be controlled by installing electrostatic precipitators in their chimneys.
Thermal Power Plant
An installation where electricity (or electrical power) is generated is called a power plant. A power plant is also called a power house.A power plant in which the heat required to make steam to drive turbines is obtained by burning fuels is called thermal power plant.
Coal is burned in a furnace F to produce heat. This heat boils the water in a boiler B to form steam. The steam formed from the boiling water build up a pressure. The hot steam at high pressure is introduced into a turbine chamber C having a steam turbine T. The steam passes over the blades of the turbine as a high pressure jet making the turbine rotate. The shaft S of turbine is connected to a generator G. When the turbine rotates, its shaft also rotates and drives the generator. The generator produces electricity. The spent steam coming out of turbine chamber is cooled. On cooling, steam condenses to form water., This water is again sent to the boiler to form fresh steam. This process is repeated again and again. We produce a major part of our electricity by burning fossil fuels.
Flowing water posses kinetic energy. The traditional use of energy of flowing water has been modified by improvements in technology and used to generate electricity.
Hydro-power plant (or Hydroelectric power plant): A power plant that produces electricity by using flowing water to rotate a turbine (which drives the generator), is called hydro power plant. The electricity produced by using the energy of falling water (or flowing water) is called hydroelectricity. A hydro power plant produces electricity. A high rise dam is built to stop the flowing river water. Due to this, a large lake or reservoir builds up behind the dam. The kinetic energy of the flowing river water is converted into the potential energy of water stored behind the dam.
The sluice gate half the height of dam are opened to allow some of the stored water to escape. The water falls down through a large height from the dam, it flows very fast. A high pressure jet of fast flowing water pushes on the blades of turbine with a great force and makes the turbine rotate rapidly. When the turbine rotates, its shaft also rotates and drives the generator. The generator produces electricity. A hydro power plant converts the potential energy of water stored in the reservoir of a tall dam into electric energy.
- Advantages of Generating Hydroelectricity
(i) The generation of electricity from flowing water does not produce any environmental pollution.
(ii) Flowing water is a renewable source of electric energy which will never get exhausted.
(iii) The construction of dams on rivers helps in controlling floods, and in irrigation.
- DISADVANTAGES OF HYDROELECTRICITY
(i) Dams built for large hydroelectric plants submerge a large area of land under water & also affects the plants and animals of the region.
(ii) Large hydroelectric power plants are expensive to build.
(iii) 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 34,000 MW.
Moving air is called wind. The wind possesses kinetic energy. it is this kinetic energy of wind which is utilized for doing work. Solar energy is responsible for the blowing of wind. The traditional use of wind energy has now been modified by the improvement in technology to generate electricity through wind powered generators.
- Wind Generator
A wind generator which is used to generate electricity by using wind energy. When the fast moving wind strikes the blades of wind turbine, then the wind turbine starts rotating continuously. The shaft of wind turbine is connected to a small generator. When the wind turbine rotates, its shaft also rotates and drives the generation. The generator produces electricity.
An important advantage of using wind energy for generating electricity is that its use does not cause any pollution. Another advantage is that wind energy is a renewable source of energy which will never get exhausted.
Advantages of wind energy
(i) The source of energy (wind) is free.
(ii) Harnessing wind energy is a pollution-free process, with no smoke, chemicals, etc., being produced. (iii) A small wind-electric plant can be set up near a factory to provide pollution-free power for its use.
Limitations of wind energy
(i) 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.
(ii) Wind is not a dependable source of energy because sometimes the air is absolutely still and at other times there are storms.
(ii) It is expensive to set up a wind farm for generating electricity because wind farms need a large area.
The sun is the source of all energy. The energy obtained from the sun is called solar energy. The solar energy which reaches the earth is absorbed by land and water bodies (like rivers, lakes and ocean) and plants. The solar energy trapped by land and water bodies causes many phenomenon in nature like winds, storms, rain, snowfall and sea waves.
The amount of solar energy received per second by one square metre area of the near earth space (exposed perpendicularly to the rays of the sun) at an average distance between the sun and the earth, is called solar constant. The value of solar constant is 1.4 kJ/s/m2 or 1.4 kW/m2 (because : 1 kJ/s =1 kW)
Solar Energy Devices
The devices which work by using solar energy (or sun’s energy) are : Solar cooker, Solar water heater, and Solar cell. A device which gets heated by using sun’s heat energy is called a solar heating device. All the solar heating devices are designed to such a way that they help in collecting as much sun’s heat rays as possible.
1. Solar Cooker
he solar cooker is a device which is used to cook food by utilising the heat energy radiated by the sun. A sola cooker consists of an insulated metal box or wooden box which is painted all black from inside. There is a thick glass sheet cover over the box and a plane mirror reflector is also attached to the box. The food to be cooked is put in metal containers which are painted black from outside.
When the sun’s rays fall on the reflector, the reflector sends them to the top of solar cooker box in the form of a strong beam of sunlight. The sun’s heat rays pass through the glass sheet cover and get absorbed by the black inside surface of the cooker box.
In this way, more and more heat rays of the sun get trapped in the box due to which the temperature in the solar cooker box rises to about 100°C to 140°C in two to three hours. This heat cooks the food materials kept in the black containers.
The important advantages of a solar cooker for cooking food are the following :
(i) The use of solar cooker for cooking food saves precious fuels like coal, kerosene and LPG.
(ii) The use of solar cooker does not produce smoke due to which it does not pollute air.
(iii) When food is cooked in solar cooker, its nutrients do not destroyed.
This is because in a solar cooker, food is cooked at a comparatively lower temperature.
(iv) In a solar cooker, up to four food items can be cooked at the same time.
Some of the important limitation of a solar cooker are given below :
(i) The solar cooker cannot be used to cook food during night time (because sunshine is not available at that time).
(ii) If the day sky is covered with clouds, even then solar cooker cannot be used to cook, food.
(iii) The direction of reflector of solar cooker has to be changed from time to time to keep it facing the sun. (iv) The box type solar cooker cannot be used for baking (making chapattis, etc.) or for frying.
2. SOLAR WATER HEATER
Solar energy can be used to heat water. In a solar water heater, sunlight is allowed to fall on a box made of a poor conductor of heat. The glass top of the box lets in sunlight and traps heat. Water enters a tube that is painted black to increase the absorption of heat. It is bent several times to increase its length inside the box. This allows the water flowing through it sufficient time to absorb heat. Hot water collects in the tank of the heater for use.
3. Solar Cell
Solar cells use the energy in sunlight to produce electricity. Thus, solar cell is a device which converts solar energy (or sun’s energy) directly into electricity.
A solar cell is usually made from silicon. A simple solar cell consists of sandwich of a ‘silicon-boron layer’ and a ‘silicon-arsenic layer’. A single solar cell can produce only a small amount of electricity. The group of solar cells is called a ‘solar cell panel’ or just ‘solar panel’. The various solar cells in a solar panel are joined together by using connecting wires made of silver metal. This is because silver is the best conductor of electricity.
The main advantages of solar cells are that they have no moving parts. They require almost no maintenance, and work quite satisfactorily without the use of any light focusing device.
Advantages of solar cells (i) Solar cells are suitable for use in remote areas where electrical power lines have not reached. (ii) Solar cells require little maintenance and last for a long time. (iii) After installation, no further cost is involved in generating electricity directly from solar cells. (iv) Solar cells are environment friendly, as they do not cause any pollution.
Disadvantage of solar cells is that they are very expensive.
This is due to the following reasons :
(i) The special grade silicon needed for making solar cells is expensive
(ii) Silver wire used to interconnect solar cells for making solar panels is expensive, and
(iii) The entire process of making solar cells is still very expensive.
- Uses of Solar Cells
(i) Solar cells are used for providing electricity in artificial satellites and space probes.
(ii) Solar cells are used for providing electricity to remote, inaccessible and isolated places where normal electricity transmission lines do not exist.
(iii) Solar cells are used for operating traffic signals, watches, calculators and toys.
4. Solar Panel
Although a solar cell provides very little power, a large number of connected solar cells, spread over a large area, can provide sufficient power for many applications. Such an arrangement of solar cells is called a solar panel. The solar cells in a solar panel are connected in such a way that the total potential difference and the total capacity to provide electric current become large.
Uses of Solar Panels: The advantage of solar panels is more in areas where the usual energy sources are not available. That is why they are used as the source of electric power in satellites. Solar panels have also been used in unmanned aircraft that fly at high altitudes for long periods, conducting scientific experiments. Experimental solar-powered cars have also been made. In many parts of India, solar panels are being used to charge rechargeable batteries during the day. At night, these batteries provide electric power for lightening, etc. They are also being used for operating traffic lights, water pumps, telephones, TV sets and radio receivers.
- Advantages of Solar Cells
(a) Solar cells are suitable for use in remote areas where electrical power lines have not reached.
(b) Solar cells require little maintenance and last for a long time.
(c) After installation, no further cost is involved in generating electricity directly from solar cells.
(d) Solar cells are environment friendly, as they do not cause any pollution.
The dead parts of plants and trees, and the waste material of animals are called biomass. Biomass includes wood, agricultural wastes (crop residues) and cow – dung. Biomass is a renewable source of energy because it is obtained from plants (or animals) which can be produced again and again.
- The Case of Wood and Charcoal
Wood is biomass. The traditional use of wood as a fuel has many disadvantages. For example (i) the burning of wood produces a lot of smoke which pollutes the air, and (ii) the calorific value (or heat value) of wood is low, being only 17 kJ/g. This means that wood produces less heat per unit mass, on burning. Wood can be converted into a much better fuel called charcoal. Charcoal is mainly carbon (C). Charcoal is a better fuel than wood because
(i) Charcoal has a higher calorific value than wood.
(ii) Charcoal does not produce smoke while burning.
(iii) Charcoal is a compact fuel which is easy to handle and convenient to use.
- The Case of Cow Dung and Biogas Cow dung is biomass. It is also known as ‘cattle dung’ or ‘animal dung’. When cow dung cakes are burnt, they produce heat. This heat is used for cooking food, etc. It is, however, not good to burn cow dung directly as a fuel because of the following disadvantages :
(i) Cow dung contains important elements like nitrogen and phosphorus, which are required by the soil to support crops.
(ii) Dung cakes produce a lot of smoke on burning which causes air pollution.
(iii) Dung cake do not burn completely, they produce a lot of ash as residue.
(iv) Dung cakes have low calorific value. Biogas is a mixture of methane. carbon dioxide, hydrogen and hydrogen sulphide.The major constituent of biogas is methane. Biogas is produced by the anaerobic degradation of animal wastes like cow dung (or plant wastes) in the presence of water.
- Biogas Plant
A biogas plant consists of a well shaped, underground tank T called digester, which is made of bricks, and has a dome shaped roof D, also made of cement and bricks . The digester is a kind of sealed tank in which there is no air. The dome of the digester tanks acts as a gas holder or storage tank for the biogas. There is a gas out let S at the top of the dome having a valve V. On the left side of the digester tank is a sloping inlet chamber I and on the right side is a rectangular outlet chamber O.
The inlet chamber is connected to a mixing tank M while the outlet chamber is connected to over flow tank F.
Cow dung and water are mixed in equal proportion in the mixing tank M to prepare the slurry. This slurry of dung and water is fed into the digester tank T through the inlet chamber.It takes about 50 to 60 days for the new gas plant to become operative. During this period, the cow dung undergoes degradation by anaerobic bacteria in the presence of water with the gradual evolution of biogas. This biogas starts collecting in the dome and forces the spent slurry to go into overflow tank F, through the outlet chamber O. From the overflow tank, the spent slurry is removed gradually. The spent dung slurry left after the extraction of biogas, is rich in nitrogen and phosphorus compounds and hence forms a good manure. The biogas which has collected in the dome of the digester tank is taken out through the outlet S and supplied to village homes through a network of pipes to be used as a cooking gas.
- The important uses of biogas are given below
(i) Biogas is used as a fuel for cooking food.
(ii) Biogas is also used for lighting.
(iii) Biogas is used as a fuel to run engines.
(iv) Biogas is used for generating electricity.
- ADVANTAGE OF BIOGAS
(i) A biogas plant is quite simple and can be easily built in rural areas.
(ii) Biogas is an excellent, clean fuel that burns without producing ash and smoke.
(iii) The spent slurry is good manure.
(iv) Biogas plants are a safe and useful way of waste disposal.
(v) Use of biogas in rural areas leads to saving of firewood, and reduces deforestation.
Energy from the sea Energy from the sea
The energy from the sea can be obtained mainly in three forms:
1. Tidal energy 2. Wave energy, and 3. Ocean thermal energy
1. Tidal energy: The rise of sea water due to gravitational pull of the moon is called high tide whereas the fall of sea water is called low tide. The tidal energy can be harnessed by constructing a tidal barrage or tidal dam across a narrow opening to the sea.
During high tide, when the level of water in the sea is high, sea water flows into the reservoir of the barrage and turns the turbines. The turbines then turn the generators to produce electricity.And during the low tide, when the level of sea water is low, the sea water stored in the barrage reservoir is allowed to flow out into the sea. This flowing water also turns the turbines and generates electricity.
2. Wave Energy:
Wave energy here means sea waves energy. Due to the blowing of wind on the surface of sea, very fast sea waves more on its surface. Due to their high speed, sea waves have a lot of kinetic energy in them. The energy of moving sea waves can be used to generate electricity. A wide variety of devices have been developed to trap sea wave energy to turn turbines and drive generators for the production of electricity.
3. OCEAN THERMAL ENERGY CONVERSION (OTEC):
Solar energy falling on the surface of the ocean warms it. The water at the surface of the ocean is warmer than the water deep below. Generally, the difference in temprature is about 20°C between the surface water and the water at a depth of 1 km. This temperature difference can be used to operate an ocean thermal energy conversion (OTEC) plant. Clearly, the ultimate source of the stored thermal energy of the ocean is the sun. In one system for OTEC, a fluid with low boiling point such as ammonia or chlorofluorocarbon (CFC) is used as the ‘working fluid’. Warm sea water is used to vaporize liquid ammonia in an evaporator. The expanding vapours of ammonia turn a turbine connected to a generator. Then the vapours go to a condenser. There, cold sea water, pumped up from the deep, is used to liquefy the ammonia. This ammonia is reused, and the cycle goes on.
‘Geo’ means earth and thermal means heat. Thus, geothermal energy is the heat energy from hot rocks present inside the earth. Geothermal energy is one of the few sources of energy that do not come directly or indirectly from solar energy (or sun’s energy) At some places in the world, the rocks at some depth below the surface of the earth are very, very hot. This heat comes from the fission of radioactive materials which are naturally present in these rocks. The places where very hot rocks occur at some depth below the surface of earth geothermal energy. Energy does not cause any pollution.
Some of the disadvantages of geothermal energy are as follows: Geothermal energy is not available everywhere it is available only in those areas where there are hot rocks near the earth’s surface.
The energy released during a nuclear reaction is called nuclear energy. Nuclear energy can be obtained by two types of nuclear reactions
1. Nuclear fission and
2. Nuclear fusion
The nuclear energy is released mainly in the form of heat.
1. Nuclear Fission
The process in which the heavy nucleus of a radioactive atom (such as uranium, plutonium or thorium) splits up into smaller nuclei when bombarded with low energy neutrons, is called nuclear fission. When uranium – 235 atoms are bombarded with slow moving neutrons, the heavy uranium nucleus breaks up to produce two medium — weight atoms, barium — 139 and krypton — 94. with the emission of 3 neutrons. A tremendous amount of energy is produced during the fission of uranium.
The energy produced during nuclear fission reactions is used for generating electricity at nuclear power plants.
Nuclear Power Plant: A power plant in which the heat required to make steam and turn turbines (to drive generations for making electricity) is obtained by nuclear reaction, is called a nuclear power plant. Most of the nuclear power plants use uranium 235 as fuel in produce heat.
In a nuclear power plant, the fission of nuclear fuel uranium 235 is carried out in a steel pressure vessels V of reactor R (Reaction is a kind of nuclear furnace). In a nuclear power plant, the fission of nuclear fuel uranium 235 is carried out in a steel pressure vessels V of reactor R (Reaction is a kind of nuclear furnace). The enriched uranium 235 rods marked A are inserted in a core made of graphite blocks inside the reactor. Graphite is called a moderator.
It slows down the speed of neutrons to make them fit for causing fission. In between the uranium rods are inserted boron rods B. Boron rods are called control rods because they absorb excess neutrons and prevent the fission reaction from going out of control. The reactor is enclosed in a concrete chamber M having thick walls to absorb the nuclear radiations.
so as to protect the outside world from the dangerous nuclear radiation. Liquid sodium is used as a coolant to transfer the heat produced in the reactor by fission to heat exchanger for converting water into steam. The controlled fission of uranium 235 in the nuclear reactor produces a lot of heat energy. Liquid sodium is pumped continuously through the pipes embedded in reactor by using a pump P. Sodium absorbs the heat produced in the reactor. This extremely hot sodium is then passed into the coil of the heat exchanger containing water.
Water absorbs heat from hot sodium and boils to form steam. The hot steam at high pressure is introduced into a turbine chamber C having a turbine T. The pressure of steam makes the turbine rotate. The shaft S of turbine is connected to a generator G. When the turbine rotates, its shaft also rotates and drives the generator. The generator roduces electricity.
2. Nuclear Fusion
The word fusion means to joint or to combine. The process in which two nuclei of light elements like that of hydrogen combine to form a heavy nucleus (like that of helium) is called nuclear fusion. A tremendous amount of energy is produced during the fusion process. When deuterium atoms (heavy hydrogen atoms of mass number 2) are heated to an extremely high temperature under extremely high pressure, then two deuterium nuclei combine together to form a heavy nucleus of helium, and a neutron is emitted. A tremendous amount of energy is liberated in this fusion reaction.
A fusion process is just the opposite of fission process. The energy produced in nuclear fusion reaction is, however, much more than that produced in a nuclear fission reaction.
3. Hydrogen Bomb
The hydrogen bomb consists of heavy isotopes of hydrogen called deuterium (2H) and tritium (3H) alongwith an element lithium – 6 (6Li). The detonation (or explosion) of hydrogen bomb is done by using an atom bomb (based on the fission of uranium – 235 or plutonium – 239) When the atom is exploded, then its fission reaction produces a lot of heat. This heat raises the temperature of deuterium and tritium to 107°C in a few microseconds. At this temperature, fusion reactions of deuterium and tritium take place producing a tremendous amount of energy. This explodes the hydrogen bomb releasing an enormous amount of energy in a very short time. This energy causes destruction of life and property.
4. The Source of Sun’s Energy
The sun is huge mass of hydrogen gas and the temperature in it is extremely high. The sun which gives us heat and light, derives its energy from the fusion of hydrogen nuclei into helium nuclei, which is going on inside it. all the time. The main nuclear fusion reaction taking place in the sun which releases a tremendous amount of energy is the fusion of 4 hydrogen atom nuclei to form a bigger nucleus of helium atom.
Nuclear fusion reactions of hydrogen are the source of sun’s energy.
An advantage of nuclear fusion reactions over nuclear fission for producing electricity is that the amount of energy released in a fusion reaction is much more than that liberated in a fission reaction.
Disadvantage of a nuclear fusion reactions is that it has not been possible to have a controlled fusion reactions so far, and to safety use the enormous heat produced during this reaction for the production of electricity.