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14. Sources of Energy

 

The law of conservation of energy: 

Energy can niether be created nor be distroyed, It can only be transformed into one form to another form. 

Main-points: 

• The total energy during a physical or chemical process is conserved.
• Energy comes in different forms and one form can be converted to another. For example, if we drop a plate from a height, the potential energy of the plate is converted mostly to sound energy when it hits the ground.
• If we light a candle, the process is highly exothermic so that the chemical energy in the wax is converted to heat energy and light energy on burning.
• Eenergy, in the usable form, is dissipated to the surroundings in less usable forms. Hence, any source of energy we use, to do work, is consumed and cannot be used again.

Good Fuels: Fuels which would do a large amount of work per unit volume or mass, be easily accessible and be easy to store and transport are called good fuels. 

Properties of good fuels: 

(i) Which produce less pollutants. 

(ii) which would do a large amount of work per unit volume or mass.

(iii) Which are easily accessible. 

(iv) Which are easy to store and transport.

(v) Which are economicals. 

 

 

 

Conventional Sources of Energy

1. fossil Fuels:

Those fuels which form by fossils of living organisms by the biochemical processes over millions of years. These fuels are called fossil fuels. 

Examples: Coal, petrolium and natural gas. 

The Dependence on coal as a source of energy: 

(i) The usase/exploitation of coal has been made the industrial revolution possible.

(ii) We are even today depended on fossil fuels like coal and petrolium for the supply of the growing demand of energy. 

(iii) Even today most of our energy requirements (about 70%) are used by fossil fuels mainly coals. 

Merits of fossil fuels as source of energy: 

(i) As domestic fuels- coals, kerosine and natural gases. 

(ii) Uses in vehicles - Petrol, diesel and CNG.

(iii) Uses of coals and other fossil fuels in thermal power plants.

Disadvantages of burning fossil fuels: 

(I) They produces smokes on burning causes air pollution.

(II) They releases oxides of carbon, nitrogen and sulpher on burning which are the main cause of acid rain. 

(III) They also releases carbon dioxide, methane and carbon monoixde which increase green house effects. 

Acid Rain: The oxides of carbon, nitrogen and sulphur that are released on burning fossil fuels, which are acidic oxides and cause acid rain. 

Disadvantages of Acid rain: 

(i) Acid rain harms trees and plants by which they dry, it also harms leaves and fruits. 

(ii) Acid rain harms our water as well as aquatic animals by which they die. 

(iii) Acid rain also harms our soil, that cause increasing its acidic nature. 

The management of pollutants produced by fossil fuels:

(i) By increasing the efficiency of the combustion process.

(ii) Using various techniques to reduce the escape of harmful gases and ashes into the surroundings.

• Weshould conserve the fossil fuels. 

Reasions for conservating fossil fuels:

(i) Fossil fuels are non-renewable source of energy.

(ii) These are in limited quantity in nature.

(iii) These form in over millions years.

The Principle of Turbines:  

Turbines work by mechanical energy, there have to provide a movement to spin its rotor-blade. This movement is aquired by moving materials like water, stem or by the air. It provides energy to rotor. This roter turns the shaft of the dynamo in order to transforming this provided mechanical energy into electric energy. This is the principle of turbines.

The process of Producing electricity: 

In the process of producing electricity, there is used the various sources of energy to turn the turbines. These are the following sources of energy.

(i) By falling water from high.

(ii) Producing stem by heating water.

(iii) By high speed wind. 

A simple Model of Thermo power Production

This process is as follows:

Turning the turbine by using energy sources

 ↓ 

Mechanical energy given by turbine to turn the shaft of dynamo

 ↓

Producing Electrical energy by the Dynamo

 

2. 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.
• There is produced energy by burning of fossil fuels in these plants, which is further converted into electrical energy. Therefore this is called thermal power plant.
• Many thermal power plants are set up near coal or oil fields. Because, the transmission of electricity is more efficient than transporting coal or petroleum over the same distance.

3. Hydro Power Plants

• The kinetic energy of falling or flowing water and the potential energy of water at a height are used in hydro power plants to convert these energy into electricity. 
• Since there are very few water-falls which could be used as a source of potential energy, hydro power plants are associated with dams. In the last century, a large number of dams were built all over the world. 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

Dam constructions and associated problems: 

(i) Opposition to the construction of Tehri Dam on the river Ganga and Sardar Sarovar project on the river Narmada.

(ii) The severe risk of flooding on beaking dam. 

(iii) The vegetation which is submerged rots under anaerobic conditions and gives rise to large amounts of methane which is also a green-house gas.

Harm resulting from the construction of dam: 

(i) Many of the agricultural lands are destroyed by construction of dam. 

(ii) Human habbitats are destroyed.

(iii) The many peoples and animals of their surrounding have to displace by which there creates the problem of satisfactory rehabilitation.

(iv) It harms the eco-system. 

Improvements in the Technology for using Conventional Sources of Energy:

There are two famous conventional sources of energy in order to improve in  the technology, e.i 

(i) Bio-Mass: 

(ii) Wind energy: 

4. Bio-Mass: 

The fuels which we obtain from plants and animals products are called bio-mass. Examples: wood, cow-dung, dry leaves and stems etc. 

- Bio-mass is a renewable source of energy. 

• They do not produce much heat on burning.
• They burn with flames.
• They produce a lot of smoke on burning. 
• The burning of bio-mass is harmful for health. 

Charcoal (Woody Coal): 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.

Properties of charcoal: 

(i) Charcoal burns without flames.

(ii) It is comparatively smokeless.

(iii) It has a higher heat generation efficiency.

Bio-gas or Gobar gas: 

The common name of bio-gas is Gobar gas, As the starting material is mainly cow-dung. 

These are the common features of bio-gas:

• Bio-gas is produced in a plant.
• The plant in which bio-gas is produced is called bio-gas or Gobar gas plant. 
• This gas is used in villages and rular areas as sources of lighting and fuels. 
• Bio-gas is an excellent fuel as it contains up to 75% methane.
• It burns without smoke.
• It leaves no residue like ash in wood, charcoal and coal burning.
• Its heating capacity is high.
• Bio-gas is also used for lighting.
• It has been an efficient fuels by using technology. 
• The slurry left behind is removed periodically and used as excellent
  manure, rich in nitrogen and phosphorous.

Formation of Bio-gas: 

Anaerobic micro-organisms that do not require oxygen decompose or break down complex compounds of the cow-dung slurry and remains of vegetables skins. such the bio-gas forms. 

 

5. Wind Energy:

Now a days, wind energy is using to produce electricity. 

Wind: Moving air is known as wind. So It has kinetic energy and having capacity to do work. 

Wind-mill : Wind mill is a plant by which electricity is generated using kinetic energy of wind. 

Structure of Wind mill: A windmill essentially consists of a structure similar to a large electric fan that is erected at some height on a rigid support. 

                                       

(Wind Mill)

Wind Energy Farm: A number of windmills are erected over a large area, which is known as wind energy farm.

Commercial use of wind mill : The energy output of each windmill in a farm is coupled together to get electricity on a commercial scale. By resulting obtained net energy is the sum of electric energy produced by the all wind mill. 

Features of Wind Energy: 

(i) Wind energy is an environment-friendly and efficient source of renewable energy.

(ii) It requires no recurring expenses for the production of electricity.

Limitation of using Wind Energy: 

(i) Wind energy farms can be established only at those places where
wind blows for the greater part of a year.

(ii) The wind speed should also be higher than 15 km/h to maintain the required speed of the turbine.

(iii) there should be some back-up facilities (like storage cells).

(iv) Establishment of wind energy farms requires large area of land.

(v) For a 1 MW generator, the farm needs about 2 hectares of land.

(vi) The initial cost of establishment of the farm is quite high.

 

Non-Conventional/Alternative Sources of Energy

Causes to look at alternative sources of energy: 

(i) The demand of energy increasing day by day, but these all demands cannot be completed by conventional sources of energy. 

(ii) Conventional sources are limited in nature. 

(iii) Conventional sources like fossil fuels are very low that can be finished in future. 

(iv) The Most of the conventional sources of energy is non-renewable. 

1. Solar Energy: 

The energy obtained from sun is known as solar energy. 

Uses of solar energy: 

There are two technologies in which solar energy is used.

(A) Solar Cooker 

(B) Solar Panel

(A) Solar Cooker:

Solar cooker is a device which is used to cook food by using solar energy. 

Principle of solar energy: 

There are two principles on which solar cooker works. 

(i)    Black colour absorbs more heat than other.

(ii)   Use of glass plate which produces green-house effect inside the cooker. 

Structure and function of Solar cooker: 

Solar cooker just like a box and its internal surfaces are coloured with black colour. Solar cookers are covered with a glass plate. Which traps heats to go out from box and shows green house effect. 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. 

(B) Solar Panel : 

​A large number of solar cells are, combined in an arrangement called solar cell panel that can deliver enough electricity for practical use.

Solar Cells: Solar cells are devices which are made of silicon and they convert solar energy to electrical energy. 

• Solar cells are made up of silicon. 
• Silver is used to interconnect the solar cells to each other to form solar panel. 
• Domestic use of solar cells is limited due to its high cost.
• 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.

Three uses of solar cells.

(i) Artificial satellites and space probes like Mars orbiters use solar cells as the main source of energy.

(ii) Radio or wireless transmission systems or TV relay stations in remote locations use solar cell panels.

(iii) Traffic signals, calculators and many toys are fitted with solar cells.

Advantage of solar cells: 

(i) They have no moving parts, require little maintenance.

(ii) They work quite satisfactorily without the use of any focussing device.

(iii) They can be set up in remote area where laying of a power transmission line
is more expensive and not commercially viable.

(iv) It is alternative source of energy. 

(v) It does not produce pollutions and does not harm environment.         

Limitation of solar cells: 

(i) These devices are useful only at certain times during the day.

(ii) They do not perform good work during rainy days. 

(iii) There is limited production of electricity by solar cells. 

(iv) They have high cost and low efficiency. 

 

The Sea Energy : 

The energy obtained from sea can be classified into three parts:

(1) Tidal Energy 

(2) Wave Enrgy 

(3) Ocean Thermal Energy 

1. Tidal Energy : The energy produced due to high and low tides is called tidal energy.

Tidal energy obtained from rising and falling of the level of sea water during tides. 

Tide :  The phenomenom of changing the level of the water of sea during the day is called tide. 

Cause of tide : 

(i) Rotation of the Earth

(ii)  The gravitational pull of the moon

Tapping of 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.

2. Wave Energy : The kinetic energy possessed by huge waves near the seashore can be trapped in a similar manner 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.

Limitation of wave energy : 

(i) Wave energy would be a viable proposition only where waves are very strong.

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 (OTEC) plants. 

Ocean-thermal-energy conversion (OTEC) plants : This is a device which is used to produce electric energy to use the heat from the difference of the temperature of top of ocean and the deeeper section. 

Tapping of Ocean Thermal Energy : 

OTEC plant is used for tapping this energy. This plant works when the temperature difference between the water at the surface and water at depths up to 2 km is 293 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.

Limitation of Ocean Thermal Energy : 

(i) The difference in temperature of the top and deeper section should be 20^०C. 

(ii) Efficient commercial exploitation is difficult.

Geothermal energy : When underground water comes in contact with the hot spot, steam is generated. The steam trapped in rocks is routed through a pipe to a turbine and used to generate electricity.

Hot spots: 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’.

Hot Springs : Sometimes hot water from that region finds outlets at the surface. Such outlets are known as hot springs.

Advantage : 

(i) The cost of production would not be much. 

(ii) Tapping of this energy is practically better for commercial use. 

Limitation : 

(i) There are very less regions of geothermal energy on the Earth. 

(ii) Reaching in such hot spots is very defficult and costly.  

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