Class 10 Physics
Sources of Energy
When we use energy in its usable form we convert the form of energy and get our work done during the process. Since we cannot reverse the change involved in this process so we cannot get back the original usable form of energy. Due to this, it becomes important to think about energy shortage and the related energy crisis.
Characteristics of a good source of energy:
- It should be able to do large amount of work for each unit of mass or volume.
- It should be easily accessible.
- It should be easily transported.
- It should be economical.
Conventional Sources of Energy:
The sources of energy which have been in use since a long time are called conventional sources of energy. Coal, petroleum, natural gas, hydel energy, wind energy and nuclear energy are considered to be the conventional sources of energy. Additionally, firewood is also a conventional source of energy but its usage is now limited to kitchens in the rural parts of India.
Coal: Coal was formed millions of years ago. The plants got buried under swamps and due to high pressure and high temperature inside the earth; they were converted into coal. Coal is the highest used energy source in India. During the days of steam engine, coal was used in steam engines. Moreover, coal was also used as kitchen fuel; before LPG became popular. Now-a-days, coal is mainly being used in the industries.
Petroleum: Petroleum was also formed millions of years ago. The animals got buried under the ocean surface and were converted into petroleum; in due course of time. Petroleum is the third major source of energy being used today. Petroleum products are used as automobile fuel and also in the industries. Natural gas mainly comes from the oil wells and is also a major source of energy.
Non-renewable Sources of Energy:
It takes millions of years for the formation of fossil fuels. Since they cannot be replenished in the foreseeable future, they are known as non-renewable sources of energy.
Renewable Sources of Energy:
Those sources of energy which can be replenished quickly are called renewable sources of energy. Hydel energy, wind energy and solar energy are examples of renewable sources of energy.
Hydel Energy: Hydel energy is produced by utilizing the kinetic energy of flowing water. Huge dams are built over a source of water. Water is collected behind the dam and released. When the water falls on the turbine; the turbine moves; because of kinetic energy of water. Thus, electricity is generated by the turbine. Electricity; thus generated is called hydel energy or hydroelectricity. Water in the reservoir is replenished with rainwater and so availability of water is not a problem for hydroelectricity.
Drawbacks of Hydel Plant: Building large dams is not good for the ecosystem. When a large dam is built, a vast tract of land in its vicinity gets submerged. This destroys a large part of vegetation and wildlife which does immense damage to the ecosystem. Moreover, when the submerged vegetation decomposes; it produces a huge amount of methane gas. Methane is a potential greenhouse gas and thus is not good for the environment.
Building large dam also affects a huge section of population which lives in the surrounding areas. Many villages need to be evacuated. Although the government comes with some rehabilitation plan for them but the displacement of people from their roots has its own costs involved.
Thermal Power Plant: In a thermal power plant, coal or petroleum is used for converting water into steam. The steam is used to run the turbine; to generate electricity.
Bio-mass: The plants and animals constitute the biomass. Firewood from plants is used as kitchen fuel. If large number of trees can be planted, then a continuous supply of firewood can be ensured. Farm waste; such as stalks of harvested plants and dung of cattle; can be used to generate methane. The decomposition of biomass produces methane; which can be channelized for useful purposes.
Bio-gas Plant: Bio-gas plant can be very useful in solving the energy need of rural areas. A bio-gas plant is a dome-like structure which is usually built from bricks and concrete. In the mixing tank; the slurry is made from cow-dung and water. The slurry then goes to the digester; which is a closed chamber. Since oxygen is absent in the digester, the anaerobes carry on their work of decomposition. The process of decomposition produces biogas. Biogas has about 70% of methane and the rest is composed of other gases. The biogas is channelized through a pipe and can be utilized as kitchen fuel and also as fuel for getting light. The slurry; left behind; is removed. It is used as manure, once it dries.
Wind Energy: Wind energy has been in use since ages. The sail boats of the pre-industrialization era used to run on wind power. Windmills have been in use; especially in Holland; since the medieval period. Now-a-days, windmills are being used to generate electricity. The kinetic energy of wind is utilize to run the turbines; which generate electricity.
At present, Germany is the leading country in terms of wind energy production and India comes at number five. In India, Tamil Nadu is the largest wind energy producing state. The largest wind farm in India is near Kanyakumari; in Tamil Nadu; which generates 380 MW of electricity.
Limitations of Wind Energy: Wind farms can only be established at those places where the wind speed is high enough and is more than 15 km/hr for most parts of the year. Wind farms need to be established on large tracts of land. The fan of the windmill has many moving parts; so cost of maintenance and repair is quite high. The fact, that it has to suffer the vagaries of the nature further compounds the problem. Initial cost of establishing a wind farm is very high.
Non-conventional Sources of Energy: Energy sources which are relatively new are called non-conventional sources of energy, e.g. nuclear power and solar energy.
Solar Energy: The sun is the main source of energy for all living beings on this earth. Even the energy in the fossil fuels has come from the sun. The sun has an endless reservoir of energy which would be available as long as the solar system is in existence. Technologies for harnessing the solar energy have been developed in recent times.
Solar Cooker: Solar cooker is very simple in design and mode of function. It is usually made from mirrors. Plain mirrors are placed inside a rectangular box. The light reflected from the plain mirrors concentrates the solar energy inside the solar cooker which generates enough heat to cook food.
Solar Furnace: Solar furnace is made like a concave mirror. Large solar furnace has many smaller mirrors to compose a very large convex mirror. The thing to be heated is place near the focus of the mirror.
Solar Cells: Solar cells are made from silicon. The solar panel converts solar energy into electrical energy which is stored in a battery; for later use.
Limitations of Solar Energy: The technologies for harnessing solar energy are at a nascent stage. At present, the cost benefit ratio for using solar energy is not conducive. Using solar energy is exhorbitantly costly.
Energy from Sea
Tidal Energy: Due to the gravitational pull of the moon, tides happen near seashores. Water rushes up near the seashore during a high tide and goes down during a low tide. Dams are built near seashores to collect the water which comes during a high tide. When the water runs back to the ocean, the flow of water can be utilized to generate electricity.
Wave Energy: Waves can also be a good source of energy. Many devices are being designed and tested to produce wave energy. For example; a hollow tower is built near the seashore. When water gushes in the tube because of wave, it forces the air upwards. The kinetic energy of air in the tube is used to run a turbine. When the wave goes down; air from up goes down the tube which is also used in running the turbine.
Ocean Thermal Energy: The water at sea surface is hot during daytime, while the water at lower level is cold. The temperature differential in water levels can be utilized to generate energy. If the temperature differential is more than 20°C, then ocean thermal energy can be utilized from that place. For this, a volatile liquid; like ammonia; is boiled using the heat from the hot water at the surface. The steam of the volatile liquid is utilized to run the turbine to generate electricity. Colder water from the surface below is utilized to condense ammonia vapour which is then channelized to the surface to repeat the cycle.
Various methods of harnessing energy from the sea are still at experimental stages.
Geothermal Energy: The molten rocks from the inside of the earth are pushed in certain regions of the earth. Such regions are called the hot spots of the earth. When groundwater comes in contact with such hot spots, lot of steam is generated. This steam can be harnessed to produce energy. Many power plants in New Zealand and USA operate on geothermal energy.
Nuclear Energy: Nuclear fission is the process during which a nucleus breaks to form two nuclei. The process generates a huge amount of energy. This phenomenon is utilized in nuclear power plants. Nuclear power is safest for the environment but the risk of damage due to accidental leaks of radiation is pretty high. Further, storage of nuclear waste is a big problem because of potential risk of radiation involved. Nonetheless, many countries are using nuclear power in a big way. India too has built many nuclear power plants. Recent accidents in the nuclear power plants in Chernobyl and Japan have forced the policymakers to rethink about the nuclear power.