THE UNIVERSE
SOURCES OF ENERGY
INTRODUCTION
From the early hours to late evening man has need for large amount of energy. He develops electrical energy from various sources of energy. Fast depleting fossil fuels make him to look for alternate sources of energy which are renewable. In this attempt he is trying to convert solar energy, geothermal energy, tidal energy, etc., into required form. In this chapter, we are going to learn about the need, types of sources and ways to convert various forms to electrical or required form of energy.
We need energy in every walk of life. Energy is required to cook our food and to light our home, for our transport, to operate all the machines and for our entertainment.
Production in factories, industries and agriculture also need energy. We need energy to do work.
Energy does not exist naturally in the form which we can use. There are primary as well as secondary sources of energy.
Energy that earth receives from the sun, in the form of heat and light, is the ultimate source of almost all our sources of energy. We shall discuss about solar, wind, bio-energy and nuclear energy in this chapter.
A material or substance that burns to provide heat energy is called ‘fuel’. Fuels are sources of energy. We take food everyday, which produces energy for doing work and to maintain body temperature. Thus, food materials are also fuels. We cook food by burning wood, coal, kerosene or cooking gas (LPG), which are also known as fuels. Petrol and diesel are fuels which are used to run automobiles. Thiokol mixed with oxidizing agents is used as rocket fuel. The most useful form of energy, electrical energy is also produced by burning fuels like coal or natural gas which converts water into steam, used to run turbine for producing electrical energy. Fuels thus play a very important role in our daily lives. We shall discuss about different types of fuels in this unit.
IMPORTANT TERMS AND CONCEPTS
1.Energy. It is defined as the ability to do work. It is expressed in Joule.
2.Mechanical energy. To do mechanical work, the energy required is called mechanical energy. It is the sun of the potential and kinetic energies.
3.Formula for energy. P. E. = mgh and K. E. = ½ mv², where m is the mass, g is he acceleration due to gravity, h is the vertical height and v is the velocity of the body.
When a mass falls down from certain height ‘h’ the P.E. store in it is converted into K.E. on reaching the ground. Similarly when a mass is thrown vertically upward, the K.E. provided is converted into P.E.
4.Heat. When we use a fuel say coal or kerosene or wood, some energy is used in igniting it and the rest is coming out in the form of heat.
5.Work. Work done is the product of force and displacement.
Work done = Force displacement. It is measured in Joule.
6.Power. The rate of doing work is called Power. . It is expressed in watt or Joule/sec.
7.Commercial Unit. Kwh is the commercial unit for electrical energy. It is related to joule as 1 Kwh = 3.6 × 106 joule.
8.Sources of energy. Any system from where energy can be tapped is called a source of energy.
9.Characters of source of energy:
(i) Capable of providing adequate amount of energy.
(ii) Should be convenient to use and easy to store and transport.
(iii) Should be capable of giving desired quality at required rate steadily over a long period.
(iv) Should release energy in mostly all forms in which the day-to-day requirement exists.
10.Conventional or non renewable sources. Energy sources which are used traditionally for many years and re to deplete over a period of time are called conventional or non-renewable sources e. g. Coal, Petroleum, Natural gas etc.
11.Non-conventional or renewable sources. Energy sources which do not deplete and are scarcely used by the population are called non-conventional or renewable sources of energy e. g. Solar energy, Wind energy, etc.
12.Electrical energy. Electrical energy is one of the widely used energies. It is generated by harnessing different sources of energy. In any conventional power plants, turbines of generators are rotated by using steam arrived by heating water from one source of energy say coal, water, gas, etc.
13.Energy Crisis. Fossil fuels like coal, petroleum, and natural gas are used extensively to fulfill energy requirements due to:
(i) Ever growing demand for fuels,
(ii) Depleting nature of fossil fuels,
(iii) The difficulty in identifying new resources.
(iv) The difficulty in unearthing the resources and
(v) Growing population.
14.Overcoming Energy Crisis. Energy crisis can be overcome by:
(i) Judicious use of the available energy
(ii) Promoting renewable energy sources
(iii) Promoting efficient conversion mechanism and
(iv) Accelerate the pace of development of technologies required for harnessing new sources.
15.Indian Deposits. In India, petroleum deposits are expected to get exhausted by 2020. The coal reserves are expected to be available for 250 years.
16.Forms of energy. Energy exists in different forms. Some of them are listed below:
(i) Muscular energy-Energy spent by muscle to do work.
(ii) Heat energy-Energy that brings warmness or coldness.
(iii) Light energy-Energy getting the vision of objects
(iv) Chemical energy-Energy due to chemical reaction
(v) Nuclear energy-Energy due to nuclear reaction like fission and fusion
(vi) Solar energy-Energy from Sun
(vii) Wind energy-Energy from moving wind.
(viii) Tidal energy-Energy from the tides in sea-water.
(ix) Geothermal energy-Energy from hot water springs found under the earth.
(x) Ocean thermal energy-Energy from temperature gradient in Ocean water.
17.Law of conservation of energy. Energy can neither be created nor destroyed; you can be transformed from one to another.
18.Solar energy is the main source. Indirectly or directly all forms of energy originate from the solar energy. So ancient man was worshipping Sun and the source / GOD. For example, Hydro-electricity can be provided to be an indirect solar energy as below:
The solar energy forms clouds by evaporating the water in lakes, rivers, oceans and other water bodies. It comes down to the surface in the form of rain and snow. It flows in rivers and oceans. The energy with flowing water can be used for getting hydro-electricity.
19.Solar energy. Nuclear fusion of deuterium is said to power the Sun. The energy that radiates out in all the direction is received to some extent by various planets and other celestial bodies. It is estimated that the earth receives only 0.00000000045792% of total solar energy. Besides heat energy, ultraviolet, gamma rays and visible light also comes from the solar energy.
20.Solar constant. The amount of solar energy received per square meter per second on the surface of earth is called Solar constant. It is approximately 1.4 (KJ/m²S).
21.Advantages of solar energy.
(i) Drying clothes is made easier.
(ii) To obtain salt from sea water by evaporation.
(iii) To get rid of moisture content in food grains.
(iv) To preserve fruits, vegetables, sea foods by sun-drying.
22.Limitations of solar energy.
(i) Energy reaching the surface is very much diffused and so the direct utility is limited.
(ii) It is not available uniformly all the time and at all the places.
(iii) It is not available in night.
(iv) Cloud formation may obstruct the reception.
23.Direct and Indirect harnessing of solar energy.
Direct sources. Conversion of solar energy to heat directly using solar cooker or electricity production using solar cells.
Indirect sources. Biomass production is a chemical reaction in the presence of solar energy. Harnessing wind, tidal and various other forms are due to the difference in temperature at different levels is an indirect source.
24.Composition of Solar energy. Solar energy consists of light and heat energies. The light consists of waves called Electromagnetic waves. Different wavelengths of visible light give different color perception. Besides visible light, ultraviolet, infrared radiations nearly 1/3rd of the sunlight consists of infrared radiation.
25.Wavelength. Length of a wave or separation between two point’s successive waves which are in same phase is called wavelength. It is expressed in meter.
26.Frequency. The number of wave motions in one second is called frequency. It is expressed in Hertz.
27.Visible light. The sunlight consists of spectrum or a group of seven colors VIBGYOR – violet, indigo, blue Green Yellow, Orange and Red. The range of wavelength from violet to red is 0.4 micron to 0.7 micron respectively. (1 micron = 10–6 m)
28.Infra red Radiations. The light of wavelength which is greater than wavelength of red are called IR radiations. They are not visible to human eye but are having the property to heat the bodies on its way. All hot bodies radiate infra-red radiations. Based on the temperature, the wavelength varies. Sun being very hot, the wavelength of IR radiations is very short in comparison to low temperature bodies on earth.
29.Solar Concentrations. In many solar devices, more intense energy from very large area is concentrated into a small area by the use of reflection. These are called solar concentrators. Generally concave mirrors or parabolic reflectors are used to concentrate energy.
If a concave mirror of focal length 15 cm. is focusing sunlight on a piece of paper at the distance of 15 cm. In a short time interval, you will observe the paper burning due to concentration of the energy at the focus of the mirror. A matchstick at focus in this case will catch fire on its own.
Fig. 7.1: Spherical Reflector
A spherical reflector is shown in the diagram. The solar energy falling over large area of mirror gets collected at the focus. A high temperature of around 180 – 200° C can be obtained, depending on the size and the quality of the reflecting surfaces. Large numbers of such concentrated are utilized to generate electricity. They are then called as solar power towers. With improved performance of solar devices using concentrators, many countries started using the devices on day-to-day basis. In 1962. India become the first country to produce solar cookers on commercial basis.
30.Greenhouse effect. The heating of atmosphere dut to the infra-red radiation trapped by CO2 is called Greenhouse effect.
(i) The sun’s rays which are feflected from the surface of the Earth have higher wavelength and rae absorbed by the greenhouse gases – CO2, water vapour and methane. This leads to heating of the atmosphere.
(ii) This effect is materialized in glass houses, since the glass cover does not allow the infrared radiations to escape from the house and heat up the inside. The same phenomena happen inside a car parked in sunlight.
(iii) Major suppliers of greenhouse gases:
(a) Volcanic eruptions(b) Respiration of living organisms
(c) Decay of dead animals(d) Burning of fossil fuels
(e) Cultivation of land
31.Solar heating Devices. The devices which get heated by the sun’s heat energy called solar heating devices. They are designed in such a manner that they collect as much sunlight as possible.
Fig. 7.2: Diagram to illustrate the principal of a solar heating device
(a) Use of Black painted surface in solar heating devices. Black surface can absorb much more heat than white reflecting surface, that is why they are used in solar heating devices. The inner walls and bottom of the box-type solar cooker are painted black to maximize absorption of heat and to minimize heat loss due to reflection and it acts as simple solar heating device.
(b) Use of Glass Sheet Cover in Solar heating device. Hot body can loose heat by conduction, convection and radiation. The black painted metal box is placed inside and insulator wooden box and covered with a transparent glass sheet in order to prevent heat loss. When heating device is placed in sunlight, glass sheet allows both visible and infra red rays to pass through it and go inside the blackened inner surface which absorbs infra red rays which cause heating effect. The glass core does not allow the infra red radiations to go out due to greenhouse effect and the temperature of heating device increases appreciably.
(c) Use of Reflector in Solar Heating Devices. In order to increase efficiency of a solar heating device, a plane mirror as a reflector is also attached to it. The reflector is used to increase are over which the solar energy energy is collect so that more and more heat rays of the sun may enter the solar heating device. Spherical reflectors are used where high temperature is to be produced They are of two types – (i) Concave reflector (ii) Parabolic reflector.
32.Solar cooker. A Solar Cooker is a device which is used to cook food using solar energy. It consists of an insulated metal box or wooden box, which is painted all black from inside. There is a thick glass cover, glass sheet as a cover over the box and a plane mirror which acts as reflector attached to the box. The food to be cooked is placed in metal container and the black painted contained is kept in box and covered with glass sheet. Solar cooker is kept in sunlight in such a way that strong beam of sunlight falls over the cooker top. The sun rays pass through the glass sheet cover and get absorbed by black surface and temperature in the box slowly rises up and reaches 100°C to 140°C by infrared rays. The heat cooks the food.
Fig. 7.3: Box type solar cooker
Advantages of Solar Cooker:
(i) It saves fuel.
(ii) It does not create pollution
(iii) The nutrients of food do not get destroyed.
Limitations of Solar Cooker:
(i) It cannot be used during night time.
(ii) It cannot be used on cloudy day.
(iii) The direction of reflector of solar cooker has to be adjusted frequently.
(iv) It cannot be used for frying.
(v) It cannot be used for making chapaties.
(vi) It takes longer time for cooking.
33.Spherical Refector Type solar cooker. In this cooker, concave, reflector or parabolic reflector is used. It concentrates its solar energy in a small region called focus and therefore quite high temperature can be produced. Therefore, food materials which require strong heating can also be cooked. It can be used for baking and frying also. We can bake chapaties and fry eggs.
34.Solar Water heater. It is device in which water is heated by using solar energy.
It consist of an insulated box B which is painted black from inside and in which copper tube is fitted in the form of a coil. These copper tubes are painted black from outside so that they may absorb hot rays of the sun more efficiently. The box is covered with glass lid so as to prevent heat loss by convection and radiation. The two ends of the copper tube of solar water heater are joined to the water storage tank.
Fig. 7.4: A domestic solar heater.
35.Production of Electricity from solar energy. The sunlight is concentrated on black painted pipes filled with water and placed at the focus of concave reflections. Due to sun’s heat, the water in the black pipes gets heated and stars boiling to produce steam which run steam turbine. Steam turbine drives a generator which provides electricity.
36.Solar Furnace. The furnace which gets heated by using sun’s energy is called solar furnace.
In solar furnace, thousands of small plane mirrors are arranged in a curve in such a way that they form a very big concave reflector which concentrates on enormous amount of solar energy at its focus. The furnace kept at the focus of the reflector becomes so high that even steel kept in it will melt.
37.Efficiency of solar heating devices. The efficiency is much lower than electric heating devices because solar energy is in much diffused form.
38.Solar Cells. It is a device which converts solar energy i.e. light energy directly into electricity. They are made up of semiconductors like silicon, germanium and selenium.
39.Semiconductors. They are those substances which have very low electrical conductivity. They are in between the good conductors and insulators. They conduct only small amount of current under ordinary conditions.
40.How solar cells are made. Solar cells are made up of silicon and gallium. In solar cell, the pieces (usually wafers) of semi conducting materials containing impurities are so fused that a potential difference develops between the two regions of semiconductors when light falls on it. The current produced by single cell measuring about 4 cm³ may be of the order of 0.4 to 0.5 V at 6.0 mA (milliampere).
Solar cell panel. It comprises of a large number of solar cells and can provide much higher power for many uses.
Uses of solar cells:
(i) All artificial satellites and space probes mainly depend upon electricity generated by solar cells.
(ii) In India, solar cells are used for lighting, operating water pumps, for running radio and television sets in remote areas.
(iii) They are being used to provide electric power to light houses and off shore oil drilling rig platforms.
(iv) Solar cells are used for calculators and electronic watches.
41.Wind Energy. The blowing wind has energy which is called wind energy. Wind is associated with kinetic energy.
Cause of Wind to blow. Solar energy is responsible for the blowing of the wind. The intensity of sun-rays is much more stronger near the equator of the earth than in the polar regions due to which the air near the surface4 of the earth in equatorial regions becomes quit hot. The hot air, being lighter, rises upward. The coolest air from the polar regions of the earth starts flowing towards the equatorial regions of the earth to fill the space vacated by the hot rising air. This flow of air from one place to another constitutes wind. The three factors responsible for blowing of wind are:
(i) The uneven heating of equatorial region and polar region of earth by sun rays.
(ii) Rotation of earth.
(iii) Local conditions.