Notes-Class 10-Science & Technology-2-Chapter-5-Towards Green Energy-Maharashtra Board

Topics to be learn : Use of various energy sources Generation of electrical energy Power generating stations Effects on environment due to Electric energy generation. Green energy or Eco-friendly energy  Conventional Sources of energy & Non-conventional Sources of energy

Energy : The capacity to do work is called energy.

• There are two different types of Energy, Potential energy and kinetic energy
• For any type of work to be done energy is required.
• Energy is a very basic and primary need. For various types of work, energy is needed in different forms.

Different forms of energy : Heat energy, light energy, electric energy, solar energy, chemical energy, nuclear energy, mechanical energy, etc. are such forms of energy which we use to fulfil our requirements.

Use of various energy sources

• Different sources of energy are used to the different forms of energy necessary for us.

• Energy can be converted from one form to another by transformations.
• This characteristic of energy is used by man to satisfy his different kinds of energy needs and able to do various types of work.

Electric Energy :

• Electric energy is used in a variety of daily items, including lamps and streetlights. Fans, an iron, a refrigerator, a water pump, a phone charger, a TV, a tape recorder, and a computer.

Generation of Electric energy:

• Michael Faraday invented the principle of electromagnetic induction. This principle is largely used in generation of electricity.
• This principle is as follows: A potential difference is generated across the conductor whenever magnetic field around a conductor changes.
• In two ways the field around a conductor is changed. (i) Keeping the conductor stationary and rotating the magnet. (ii) Keeping the magnet stationary and changing the field around the conductor.
• In both cases there is creation of potential difference across the conductor.
• In Generator the magnetic field around conducting wires is changed and this creates the potential difference. This results in the formation of electric energy.
• The work of electric generators are based on this principle and generate the electrical power.
• In commercial power generation plants Large Generator rotate by turbines, Flow of liquid or gas is directed on the turbine blades to rotate it. Kinetic energy of flow rotate turbine. Turbine having blades rotates the magnet in the electric generator. Due to rotation of magnet potential difference is generated across the conductor whenever magnetic field around a conductor changes, results in production of Electric energy.

There are different types of power generating stations depending upon the type of energy source that is used to rotate the turbine.

(1) Thermal energy based electric power station :

• In thermal power plant the turbines are rotated using steam. Here the coal is burnt.
• The heat energy liberated from this burning is used to heat the water in the boiler. This water produces steam of very high temperature and pressure.
• The kinetic energy in the steam rotates the turbines.
• The rotation of turbines produces its own mechanical kinetic energy.
• The generators connected to turbines produce electrical energy.
• The steam is condensed in a condenser and converted back into water. In this way in thermal power plant, thermal energy to kinetic energy, kinetic energy into mechanical energy and mechanical energy to electrical energy, are the conversions that take place.
• The steam is reused by converting it into water → Water recirculated to the boiler.

• Such power plants are called thermal power plants because thermal energy is used here to generate electrical energy.
• The chemical energy in the coal is converted into electrical energy gradually through several steps.

Problems caused due to thermal power plants :

• Burning of coal results into air pollution : Carbon dioxide, sulphur dioxide and nitrogen oxide, etc. are gases harmful to the health.
• Soot particles are released due to such burning.
• Serious health problems arise due to toxic gases and soot particles. Especially the respiratory system is affected.
• The coal reserves are limited. They are exhaustible and hence there would be problems about its availability.

Q. Why is the energy in the coal called chemical energy?

Q. Why steam is used to rotate the turbine?

(2) Power plant based on Nuclear Energy :

• In Nuclear Power plant, energy released by fission of nuclei of Uranium or Plutonium atoms is used to generate the steam of high temperature and high pressure.
• Steam turbine is used to rotate the generator in the power plant based on nuclear energy.
• The turbine is rotated due to the energy in the steam. This further drives the generator to produce electricity.

Flow chart of nuclear power plant :

Energy transformation in nuclear power plant

• Energy in the atoms → nuclear energy → converted into thermal energy → converted into kinetic energy of steam → converted into kinetic energy of turbine → converted into electrical energy.

Formation of nuclear energy :

• Upon bombardment by neutrons on atom of Uranium-235, absorption of neutron takes place. It converts Uranium-235 into its isotope Uranium-236,
• Being extremely unstable, Uranium-236 transforms into Barium and Krypton atoms through a process of fission. This releases three neutrons and 200 MeV energy.
• Three more Uranium-235 atoms undergo fission due to three neutrons generated in this process, Thus, more fission releases more energy,
• Thus a chain reaction takes place in which the process of fission of Uranium -235 atoms continues,
• In this way a controlled chain reaction is carried out to release thermal energy, which in turn is used for generating electric energy.

Advantages of nuclear energy :

• Fossil fuel like coal is not used in a nuclear power plant. Hence air pollution does not occur.
• If sufficient nuclear fuel is available, it becomes a good source of electrical energy.

Disadvantages of nuclear energy :

• Radioactive and harmful radiations are emitted after fission of nuclei occurs.
• The nuclear waste of radioactive substance requires very safe disposal.
• Very fatal accidents can happen in power plant which emits very harmful radiations.

Nuclear fission process :

• There are proton and neutron in the nucleus of an atom.
• During nuclear fission, the Nucleus undergoes fission either due to natural radiations or due to bombardment of other neutrons on it.
• The fission generates the energy which is known as nuclear energy or atomic energy.

(3) Power generation plant based on energy of natural gas:

• Combustion of natural gas generates very high temperature and pressure. This gas is used to run the turbine.
• In power generation plant based on energy of natural gas four main sections are present. (i) Compressor (ii) Combustion chamber (iii) Turbine (iv) Generator

Arrangement in power plant based on energy of natural gas :

• Into the combustion chamber pressurized air is introduced by a compressor →  the natural gas burns due to air→ high temperature and pressure →  runs the turbine →  Turbine drives generator →  Electricity is produced.

 Step-by-step transformation of energy in this plant :

Advantages of Using of natural gas in thermal power plant :

• More efficiency than coal power plants
• Less polluting as there is no sulphur in natural gas.
• Less pollution by burning of natural gas.

Electric energy generation and environment

Environment degradation:

• Fossil fuels like coal, natural gas and nuclear fuels like uranium and plutonium are hazardous and are polluting.
• Thus, electrical energy obtained by burning these is not environment-friendly.
• Excessive use of these fuels cause environmental degradation.

Pollution :

• Incomplete combustion of fuels releases Carbon monoxide which is harmful and gives adverse effects on health
• Burning of fossil fuels like coal, and natural gas, emitted toxic gases and soot Particles in air due to this air pollution increases causes, problems in respiratory system, like asthma.
• Due to burning of fuels, increase in percentage of carbon dioxide in the air, Global warming and climate change seen.
• Burning of fuels like coal, diesel, petrol, etc. releases Nitrogen dioxide cause acid-rain.

Non-renewable nature :

• Use of energy is unavoidable in our daily life but controlled and careful use is essential.
• The formation of fossils fuels such as coal, hydrocarbons, crude oil and natural gases (LPG and CNG) took millions of years.
• But their excessive use is depleting these fuels very rapidly. The coal reserves in the world are thought to last in next 200 years and the natural gas reserves for about 200-300 years.
• Problems about nuclear energy are tremendous. It emits toxic materials, Disposal of nuclear waste is difficult problems, Accident In nuclear power plant can be highly disastrous,

Looking at the problems in electricity generation using fuels like coal, natural gas and nuclear fuels, the world is now heading towards environment friendly energy i.e. green energy.

Green energy or Eco-friendly energy :

Method of energy production in which there is no pollution are the ways of green energy,

• Energy from water reservoir,
• Energy from wind
• Energy from sunlight
• Energy from biofuels

etc. are eco-friendly alternatives of energy production,

The sources of such energy are perpetual and sustainable.

These types of energy production are pollution free and eco-friendly.

The entire globe is inclining towards green energy.

Hydroelectric Energy :

• Hydroelectric energy is a conventional type of energy.
• Kinetic energy in flowing water or the potential energy in water reservoir is a conventional source of energy.
• In hydroelectric power plant, the potential energy in water stored in dam is converted into kinetic energy of water.

Flowing water → Kinetic energy + Water reservoir → Potential energy.

Process of Hydro electric energy generation :

Hydroelectric power plant → Stored water's potential energy → Fast flowing water → Converted into kinetic energy of water → Such speedy water from dam is brought. → to the turbine at the bottom level → Kinetic energy of the flowing water → drives the turbine → turbine then drives the generator → electricity is generated.

Different Stages in hydroelectric power plant :

Energy Transformation in hydroelectric power plant :

Advantages of hydroelectric power generation :

• Since there is no combustion, there is no pollution.
• Possible to generate electricity as and when required.
• Water supply can also be achieved due to dam.
• Rains replenish the stored reservoir of the water.

Disadvantages of hydroelectric power generation :

• Some villages or settlements are submerged.
• People are displaced and their rehabilitation is the major problem.
• Fertile land, agricultural plots forests and biodiversity is lost forever.
• Obstruction of the flowing water leads to adverse effect on the resident aquatic organisms.

 Electricity generation using wind-energy :

• The kinetic energy of wind can be converted to electrical energy with the help of wind-turbine.
• Such kinetic energy of wind was used for lifting of water, for driving floor mill, etc. in olden times.
• When the wind strikes the blades of the turbine, the blades rotate.
• The axle of the turbine and electric generator are connected through a gear-box which increases the rotations per unit time.
• The rotating blades drive the turbine which in turn drives the generator and produces electricity,
• By using wind turbines can produce electricity in the range less than 1 kW to about 7 MW (7000 kW).

Stages in electric generator using wind energy :

Transformation of energy in an electric generator using wind energy :

Installation of windmills :

To produce electricity from wind energy windmills are required to install. The installation of windmills depends upon following factors :

• The wind speed that is present at the installation site.
• Regional variables.
• Installation of wind turbines is done when it is appropriate.
• The seashore is the best location for installations because the wind speed is higher there.
• Wind energy is a clean energy source, but its utilisation is constrained by issues with wind velocity.

Electric Energy generation using solar energy :

Solar energy can be used to make electric energy in following two ways :

• Using radiations from the sunlight, without using a transformer, it is trapped directly into solar photovoltaic cells. Electrical energy is produced from solar energy due to direct conversion occurring in photovoltaic cells.
• Solar energy is converted into thermal energy. By using this thermal energy turbine-generator is rotated and by that thermal energy electricity is generated.

Solar photovoltaic cell :

• Solar photovoltaic effect is the conversion of solar energy directly into electrical energy.
• Such generated energy is DC in nature.
• A special type of material called semiconductor (e.g. silicon) is used in making solar cells.
• The potential difference available from a solar cell is independent of its area.

Connections of solar cells :

(a) Solar cells connected in series:

• When two solar cells are connected in series, the potential difference obtained from both the cells is sum of the potential differences of individual solar cells.
• The current generated from combination in series is equal to the current from an individual cell.
• When solar cells are connected in series, currents from the individual cells cannot be added.

(b) Solar cells connected in Parallel:

• When two solar cells are connected in parallel, the potential difference obtained from this combination is the same as the potential difference obtained from individual cell.
• The potential differences cannot be added when the combination is in parallel.
• The current generated from two cells in parallel is the summation of the currents from an individual cell.

Solar panel :

• Solar panels are formed by connecting many solar cells in series and in parallel.
• Required potential difference and the current can be obtained by making solar panels by connecting solar cells in series and in parallel.
• The basic unit in solar electric plant → Solar cell → Solar panel → By joining in a series → String → Many strings joined in parallels → Solar array.
• Calculators running on solar energy need marginal power, whereas power stations need power in MW capacity.
• The DC power is available from the solar cells.
• Therefore, it can be used in applications like electric LED (Light Emitting Diodes) and other appliances that work on DC power.
• Most of the domestic appliances as well as industrial equipment run on AC power.
• Therefore, DC solar power is converted to AC power with the help of an inverter.
• Solar energy is available only in presence of sunlight, therefore it is stored in batteries for later use.

• Many solar panels together generate energy that is needed.
• The DC power generated → converted to AC power → with help of a transformer → voltage and current levels → energy obtained → fed into the electricity distribution network.

Advantages of solar energy :

• Generation of energy without any fuel combustion and without any pollution.

Problem of solar energy :

• Available only on sunny days and during day-time only.

Solar Thermal power plant :

• Solar radiation can be used to produce thermal energy.
• This solar thermal energy is used for electricity production.
• Solar radiation is absorbed by many reflectors that reflect and concentrate it.
• This solar energy is converted into heat energy which is then used to make steam which drives turbines and generate electricity through generators.

Different stages in solar thermal power plant :