1. • Fossil fuels – Fossil fuels are conventional sources of energy. Let us quickly look at some important points about fossil fuels:
     1. Formed by decomposition of dead remains of living organisms.
     2. Take millions of years for their formation and very difficult to replenish.
     3. Therefore, they are non-renewable sources of energy.
     4. Uses –
        • Used in gas stoves for cooking.
        • Fuel in vehicles
        • For generating electricity
        • In various industries
     5. Disadvantages-
        • Non-renewable source, hence may exhaust in near future
        • Harmful chemicals like oxides of carbon, nitrogen and sulphur are released on burning fossil fuels
        • Causes air pollution and acid rains
        • Causes greenhouse effect
        • threaten the ecological balance of the areas around fuel extraction

Let us now see how fossil fuels are used in industries for generating electricity.

• The simplest turbines have one moving part, a rotor-blade assembly.
• The moving fluid acts on the blades to spin them and impart energy to the rotor.
• Thus, we see that basically we need to move the fan, the rotor blade, with speed which would turn the shaft of the dynamo and convert the mechanical energy into electrical energy.

This similar principle is used in thermal and hydro power plants.

b. Hydro Power Plants – Hydro power plants convert the potential energy of falling water into electricity.

• high-rise dams are constructed on the river to obstruct the flow of water
• Water is collected in large reservoirs.
• The water level rises and the kinetic energy of flowing water gets transformed into potential energy.
• Water is carried to turbine (which is at the bottom), through pipes.
• These turbines are then connected to generator and powerhouse, and the electricity is supplied through power lines.

Since the water in the reservoir would be refilled each time it rains, it is a renewable source of energy.

Disadvantages of constructing dams

These are few disadvantages of constructing dams due to which construction of Tehri Dam on the river Ganga and Sardar Sarovar project on the river Narmada  was also opposed.

• Dams can be constructed only in a limited number of places, preferably in hilly terrains
• Large areas of agricultural land and human habitation are to be sacrificed.
• Large ecosystems are destroyed when submerged under the water in dams.
• Release of large amounts of methane, due to submerged vegetation, which increases greenhouse effect.
• Problem of rehabilitation of displaced people.

Biomass

The animal and plant products, which are sources of fuel, are known as biomass. For example, cow dung cake is used as fuel for various household purposes. But these fuels produce less heat, and more smoke. Therefore, new methods are used to make them more efficient. For example –

1. Charcoal is produced when wood is burnt in a limited supply of oxygen and water. Charcoal burns without flames, is comparatively smokeless and has a higher heat generation efficiency.
2. Another way is to produce biogas by decomposing cow dung cakes, agricultural wastes, vegetable wastes and sewage, in the absence of oxygen. Here you can see the structure of a biogas plant –

Structure and working of a Biogas plant

1. Slurry is made by mixing animal dung with an equal amount of water in a mixing tank.
2. Slurry is fed into the underground digester tank through a sloping inlet chamber.
3. Anaerobic microorganisms that do not require oxygen to decompose or break down complex compounds of the cow dung slurry to produce bio gas in the digester.
4. The produced biogas is collected inside the dome built over the digester tank.
5. As more and more biogas starts collecting, the pressure exerted by the biogas increases. This forces the spent slurry into overflow tank via outlet chamber.
6. The collected biogas is taken out through the outlet valve and is supplied wherever required.
7. The spent slurry is periodically removed and is used as a manure for plants.
8. To get continuous supply of gas, a prepared slurry is fed into the plant regularly.

Biogas is considered as a good fuel and these are the reasons for it –

Advantages of Biogas

1. high calorific value.
2. burns without smoke, leaves no residue and therefore causes no atmospheric pollution.
3. slurry left behind is used as an excellent manure, rich in nitrogen and phosphorus.
4. can be produced anywhere with less production cost and does not involve any running cost.
5. provides a safe and efficient method of waste disposal.

Wind Energy

The kinetic energy of wind is used to do work. For example- a windmill is a turbine which rotates due to the force exerted by wind on its adjustable blades.In a windmill, the kinetic energy of wind can be either used to do some useful mechanical work or to generate electricity.

Advantages and Disadvantages of harnessing Wind Energy

• environment-friendly
• efficient source of renewable energy.
• no recurring expenses for the production of electricity.

Limitations of harnessing wind energy-

• wind energy farms can be established only at those places where wind blows for the greater part of a year.
• The wind speed should be higher than 15 km/h
• need some backup facilities (like storage cells) for the energy needs when there is no wind.
• Requires large area of land.
• Requires high level of maintenance.
• Initial cost of set-up is very high.

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