CONVENTIONAL (TRADITIONAL) SOURCES OF ENERGY
Fossil Fuels
- Ancient energy sources: Wood (most common source of heat energy), energy of flowing water, and wind.
- The exploitation of coal led to the industrial revolution. It increased the global demand for energy.
- The demand for energy was largely met by fossil fuels (coal and petroleum). But they are non-renewable sources because they were formed over millions of years ago and have only limited reserves. So we need to conserve them, and alternate sources must be explored.
- Disadvantages of burning fossil fuels:
- Air pollution.
- Release of acidic oxides of carbon, nitrogen, and sulphur. They cause acid rain, which affects water and soil.
- Greenhouse effect of gases like CO2.
- The pollution caused by fossil fuels can be reduced by increasing the efficiency of combustion and using various techniques to reduce the release of harmful gases and ashes.
- Fossil fuels are also used to generate electricity. This can be demonstrated by the following activity:
- Make three slits in a table-tennis ball and put semi-circular fins cut out of a metal sheet into them.
- Pivot the tennis ball on an axle through its center with a straight metal wire fixed to a rigid support. Ensure that the tennis ball rotates freely about the axle.
- Connect a cycle dynamo and a bulb in series to this.
- Direct a jet of water or steam produced in a pressure cooker at the fins. The bulb glows.
- This is the model of a turbine for generating electricity. The simplest turbines have a moving part called a rotor-blade (fan). The moving fluid spins the blades and imparts energy to the rotor. It turns the shaft of the dynamo and converts mechanical energy into electrical energy.
Thermal Power Plant
- It is the power station where fuel is burnt to produce heat energy, which is converted into electrical energy.
- Burning of fossil fuels → heats water → produces steam → runs the turbine → generates electricity.
- Many thermal power plants are set up near coal or oil fields because transmission of electricity is more efficient than transporting coal or petroleum.
Hydro Power Plants
- Here, kinetic energy of flowing water or potential energy of water at a height is used.
- Hydro power plants convert the potential energy of falling water into electricity.
- A quarter of the energy requirement in India is met by hydropower plants.
- There are only a few waterfalls as a source of potential energy. So, hydro power plants are associated with dams.
- To produce hydel electricity, dams are constructed on the river. They obstruct water flow and collect in larger reservoirs. The kinetic energy of flowing water is transformed into potential energy. Dam water is carried through pipes to the turbine at the bottom of the dam.
- Since the water in the reservoir is refilled by rainfall, hydroelectricity sources are not used up. So hydro power is a renewable source of energy.
- Problems of constructing big dams:
- They can be constructed only in a few places, such as hilly terrains.
- Agricultural land and human habitation will be submerged. Large ecosystems are destroyed when submerged under water in dams.
- The submerged vegetation rots under anaerobic conditions to produce methane (a greenhouse gas).
- Opposition to the construction of Tehri Dam on the Ganga River and the Sardar Sarovar project on the Narmada River is due to such problems.
Improvements in the Technology for Using Conventional Sources of Energy
Biomass
- Biomass is plant or animal material used as fuel, e.g., firewood, cow-dung cakes, etc.
- It is a renewable source of energy.
- However, they do not produce much heat on burning and release a lot of smoke. So, technological inputs are used to improve their efficiency.
- When wood is burnt in a limited supply of oxygen, water and volatile materials present in it get removed to give charcoal. Charcoal burns without flames, is comparatively smokeless, and has higher heat generation.
- Cow-dung, crop residues, vegetable waste, sewage, etc., are decomposed in the absence of oxygen to give biogas. Here, the starting material is mainly cow-dung, so it is popularly known as gobar gas.
- The biogas plant has a dome-like structure (gas tank). A slurry of cow-dung and water is made in the mixing tank. It is fed into a digester (a sealed chamber without oxygen).
- Anaerobic microbes decompose complex compounds of the slurry and generate gases like methane, hydrogen, CO2, and H2S. These are the ingredients of biogas. It is stored in the gas tank and drawn through pipes.
- Biogas is an excellent fuel because:
- It contains up to 75% methane.
- It burns without smoke and leaves no residue (ash).
- It has high heating capacity.
- It is also used for lighting.
- Other advantages of biogas plant:
- The slurry left behind is used as manure, rich in nitrogen and phosphorus.
- Safe waste disposal of bio-waste and sewage.
Wind Energy
- Wind is the movement of air caused by unequal heating of the landmass and water bodies by solar radiation.
- The wind’s kinetic energy was harnessed by windmills to do mechanical work, e.g., in a water-lifting pump, the rotatory motion of the windmill is used to lift water from a well.
- Today, wind energy is also used to generate electricity.
- A windmill consists of a rotor with blades on a support. Its rotatory motion turns the turbine of an electric generator.
- The output of a single windmill is very small and cannot be used commercially. So, many windmills are erected over a large area. This is called a wind energy farm. The energy output of each windmill is coupled together to get electricity on a commercial scale.
- Wind energy is environment-friendly and renewable. It has no recurring expenses for the production of electricity.
- Limitations in harnessing wind energy:
- Wind energy farms can be established only at places where wind blows for the greater part of a year.
- Wind speed should be higher than 15 km/h to maintain the required speed of the turbine.
- Needs backup facilities (like storage cells) to meet energy needs when there is no wind.
- Wind energy farms need a large land area (2 hectares for a 1 MW generator). The initial cost is very high.
- Towers and blades are exposed to rain, sun, storms, and cyclones, so they need a high level of maintenance.
Denmark (country of winds) generates >25% of its electricity through windmills. In terms of total output, Germany is the leader. India ranks 5th. The largest wind energy farm (380 MW electricity) was established near Kanyakumari (Tamil Nadu). 45,000 MW of electricity can be generated if India’s wind potential is fully exploited.