Conventional Sources of Energy
The global demand for energy has increased over the years due to rapid industrialization. It was met largely by the fossil fuels – coal and petroleum. But these are non-renewable and hence will get exhausted if consumed at the present rate. Alternate sources of energy, therefore, need to be explored.
Fossil Fuels
Coal, petroleum and natural gas are known as fossil fuels as they were formed by the fossilized remains of plants of animals. Coal is the fossilized remains of plants while petroleum is the fossilized remains of marine plants and animals. Fossil fuels are classified as non-renewable sources of energy.
Natural Gas
Natural gas is another fossil fuel found with petroleum in oil wells. It contains mainly methane and can be burnt easily to produce heat. When it is subjected to high pressure, it is known as Compressed Natural Gas or CNG. It is an environment-friendly gas as its combustion does not produce any polluting gases or particulate matter. It can also serve as an excellent feed stock for the production of fertilizer and petrochemicals and also as a fuel.
Example 1.
Case-Based:
Take a table tennis ball and make three slits into it. Put semicircular fins cut out of a metal sheet into these slits. Pivot the tennis ball on an axle through its centre with a straight metal wire fixed to a rigid support. Ensure that the tennis ball rotates freely about the axle.
Now connect a cycle dynamo to this. Connect a bulb in series. Direct a jet of water or steam produced in a pressure cooker at the fins as shown in figure below. Note your observations.
(A) Select the incorrect observations from the first activity:
The figure in first activity denotes:
(I) the figure denotes a turbine for generating electricity.
(II) the simplest turbines have two moving parts, a rotor-blade assembly.
(III) the moving fluid acts on the blades to spin them and impart energy to the rotor.
(IV) We need to move the fan, the rotor blade, with speed which would turn the shaft of the dynamo and convert the electrical energy into mechanical energy.
(a) Both (I) and (II)
(b) Both (II) and (III)
(c) Both (III) and (IV)
(d) Both (II) and (IV)
Answer:
(d) Both (II) and (IV)
Explanation: The figure denotes a turbine for generating electricity which consists of one moving part, a rotor-blade assembly. The fan, the rotor blade, is moved with speed which would turn the shaft of the dynamo and convert the mechanical energy into electrical energy.
(B) The source of energy which cannot be harnessed efficiently to run the turbine and generat elec¬tricity is:
(a) Fossil fuels
(b) Solar energy
(c) Wind energy
(d) Water
Answer:
(b) Solar energy
Explanation: Fossil fuel coal is used in thermaL power plant to generate electricity whereas water is used in hydro power plants to generate electricity. Wind energy farms are installed for generating electricity from wind mills. Solar energy can be used for generating electricity using solar cells but it cannot run turbine to generate electricity.
(C) What is observed when a jet of water or steam produced in a pressure cooker is directed at the fins in the first activity?
Answer:
When a jet of water or steam produced in a pressure cooker is directed at the fins, the mov¬ing fluid acts on the blades to spin them and impart energy to the rotor.
(D) What is the difference in the way your grand-parents or elders got water for their daily needs when they were young and the present times?
Answer:
Our grandparents and elders used to fetch water from wells or ponds in their village and later using handpumps. In the present time, water is supplied to homes from water treatment plants using pipelines.
(E) Assertion (A): More energy from external sources was spent by our grand¬parents and elders in going to school when they were young as compared to present day students going to school.
Reason (R): School vans and buses use fossil fuels such as petroleum and CNG.
(a) Both (A) and (R) are true and (R) is the correct explanation of the assertion.
(b) Both (A) and (R) are true, but (R) is not the correct explanation of the assertion.
(c) (A) is true, but (R) is false.
(d) (A) is false, but (R) is true.
Answer:
(d) (A) is false, but (R) is true.
Explanation: Our grandparents and elders used to either walk or used bicycle to go to their school and hence they used no external source of energy. Whereas, present day students go to school either by school buses or vans which consume fossil fuels and hence consume more energy from external sources.
Thermal Power Plant
Large amounts offossilfuelare burnt in power stations to heat up water to produce steam which runs the turbine to generate electricity. Thermal power plants are set up near coal or oil fields as it is more efficient to transmit electricity as compared to transport coal or petroleum.
Energy from Water
Water flowing through rivers is an important source of energy which has been utilized for a variety of purposes. The energy of flowing water is a manifestation of solar energy. We are familiar with the energy transformations taking place during the water cycle. The energy of flowing water is used to generate electricity on a large scale at hydroelectric power plants.
Hydroelectric Power Plants
Principle: The kinetic energy of flowing water is transformed into potential energy by constructing high rise dams on rivers. The stored water is made to fall on turbine blades which rotate the armature of the electric generators to produce electricity.
Advantages and Uses of Hydroelectricity
- It does not cause any pollution.
- It uses water which is a renewable source of energy.
Limitations of Hydroelectric Power Plants
- These can be constructed only at a Limited number of places.
- When dams are built on rivers, large land areas get submerged which causes environmental and social problems.
- It destroys the natural habitat of plants and animals and even human habitations.
- It can adversely affect the ecosystem of adjoining as well as areas downstream.
- It decreases fertility of soil in downstream areas.
- It creates the problem of satisfactory rehabilitation of displaced people.
Improvements in the Technology for Using Conventional Sources of Energy Biomass
Biomass is a form in which solar energy manifests itself. Plants and animals and excreta of living organisms and their bodies contribute to the biomass. It also includes wastes from tree, wood, cow dung, charcoal and baggage (residue of sugarcane after extracting itsjuice).
- Biogas is an excellent fuel as it contains up to 75% methane.
- Charcoal burns without flames and is relatively smokeless
- It does not leave any residue like ash in wood, charcoal and coal burning.
- It has a high heating capacity.
Biomass as fuel: Wood is used as a source of heat. Firewood is burnt in traditional chulhas for cooking and heating water.
Comparison between traditional chulhas and smokeless chulhas:
| Traditional Chuthas | Smokeless Chuthas |
| 1. Incomplete burning of firewood produces smoke. | 1. Complete combustion of firewood takes place which produces no smoke. |
| 2. These are inefficient as only 8-10% energy of the fuel gets used. | 2. These ore highly effcient. |
| 3. These need more fuel. | 3. These need Less fuel |
| 4. These are not attached with chimneys. | 4. These are attached with chimneys. |
Charcoal
Charcoal is another commonly used fuel that is obtained from wood. When wood is burnt in a Limited supply of oxygen, water and volatile materials present in it get removed and the charcoal is left behind as a residue. This process of burning wood in a limited supply of oxygen is called destructive distillation of wood. Charcoal is an expensive fuel as destructive distillation of one kilogram of wood yields only 0.25 kg charcoal.
Advantages of Charcoal over Wood
- Charcoal burns easily, producing no smoke.
- It gives twice as much heat as is obtained by burning same mass of wood. These qualities make charcoal a better fuel than wood.
Biogas Plants
In a biogas plant, degradation of biomass is carried out by anaerobic micro-organisms called anaerobic bacteria in the presence of water but in the absence of oxygen. The components of a biogas plants are:
Mixing Tank: Equal amounts of animal dung and water are mixed in this tank. This mixture is called slurry which is then fed to the digester tank.
Digester tank: The anaerobic micro-organisms break down the complex compounds of the biomass in this underground tank. The digesters are designed like a sealed chamber. This process takes about 50-60 days during which gases like methane, carbon dioxide, hydrogen and hydrogen suLphide are produced.
Outlet for gas: As more and more biogas is formed, it is taken out through the outlet pipe.
Overflow tank: When more and more biogas is formed inside the digester, it exerts pressure on the slurry in the digester tank which forces the spent slurry to the overflow tank.
Advantages of biogas plants
- The main constituent of biogas is methane, which is an excellent fuel and burns without producing smoke.
- Burning of biogas does not leave any residue.
- Biogas can be used for heating, lighting and for producing electricity.
- The slurry which is left behind is an excellent manure as it is rich in nitrogenous and phosphorus compounds.
- It gives us a safe method to dispose off wastes.
Wind Energy
Moving air is called wind. Sun’s energy is responsible for the movement of air from one region to another thus constituting wind. Wind possesses kinetic energy as it is moving air. Some of the common applications of wind energy are in winnowing and windmills.
Windmills
Principle: Windmills are devices which convert wind energy into mechanical or electrical energy and can therefore be used for working water lifting pumps, flour mills and electric generators.
Construction: It consists of a structure similar to a Large electric fan that is erected at some height on a rigid support. The blades of a windmill are designed to create a pressure difference between its different regions when wind strikes them. This pressure difference creates a turning effect due to which the blades rotate with a speed which depends upon the wind velocity.
Wind energy farm: When a large number of windmills are erected over a large area and the energy output of each windmill is coupled together to generate electricity on a commercial scale, this is known as a wind energy farm. The wind power potential of our country is about 20,000 MW. The largest wind energy farm near Kanyakumari in Tamil Nadu can generate 380 MW of electricity.
Advantages of windmills:
- It uses wind energy which a renewable source of energy.
- Its use does not cause any environmental pollution.
- It requires no recurring expenses for the production of electricity.
Limitations of windmill:
- Windmills can be established only at those places where wind blows for most part of the year.
- The wind should be strong and steady to maintain desired levels of production. The minimum wind velocity required for a functional windmill is about 15 km/h.
- Large areas of land are required to establish wind energy farms. An area of about 2 hectares is required for a 1 MW generator.
- The setting up of wind energy farms is quite costly.
- There should be some back-up facilities to take care of the energy needs during a period when there is no wind.
- They need a high level of maintenance as the tower and blades are exposed to rain, sun storm and cyclone etc.
Example 2.
How has the traditional use of wind and water energy been modified for our convenience?
Answer:
Wind and water energy have been used tra-ditionally for our energy requirements. But, the traditional use of wind and water energy have been modified to generate electricity on a large scale by installing wind energy farms and dams.