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

Coal is used as a fuel in thermal power plant. Coal contains Chemical energy. Upon burning coal releases heat energy. This heat energy is used in thermal power plant to generate electricity. Problems associated with this type of power generation are:

• Air pollution caused due to burning of coal: Burning of coal emits gases like carbon dioxide, sulphur oxide and nitrogen oxide which are harmful & toxic to health of living beings
• Release of soot particles in the environment: Along with the gases released due to burning of coal, soot particles are released in the environment which can cause fatal respiratory problems such as asthma.
• Coal is non-renewable source of energy. So, this method of power generation will put a limit on the availability of coal in future.

Nuclear power plants and solar power plants, used thermal energy for power generation other than thermal power plants. Different ways of generating thermal energy are:

• Using fossil fuels: By burning fossil fuels such as coal, petroleum, the chemical energy stored in them is converted into thermal energy.
• Combustion of natural gas: Chemical energy in natural gas is converted into thermal energy. Upon combustion natural gas produces gas, which is used to run the turbine. This gas is under high pressure and high temperature.
• Nuclear fuels: In nuclear power plant the energy is released by fission of nuclei atoms. Controlled chain reaction in nuclear power plants releases huge amount of thermal energy. This energy is used to generate steam of high temperature and pressure. The turbine runs  on this steam energy and turbine drives the generator.
• Solar Power: In solar Power plant thermal energy is generated with the helpof solar radiations. Solar radiations concentrated, reflected and absorbed in aborbers where it gets converted to thermal energy. 

The steps of energy conversion are maximum in thermal power generation:

(i) Thermal energy based power generation: It involves 5 steps of energy conversion.

Fuel Energy → thermal energy → kinetic energy in steam → kinetic energy in turbine → electrical energy

(ii)The power generation using solar photovoltaic cell  & wind turbine involves minimum number of steps for energy conversion

Green energy is that energy which does not pollute the environment and is renewable in nature. The energy sources such as sunlight, wind, rain, tides, etc. can be called as green energy. This is because these are readily available on Earth, can be naturally replenished and do not even harm the environment much.

• Fossil fuels are non renewable sources of energy. These are getting depleted rapidly.
• Also, the usage of the fossil fuels for energy generation adversely impacts the environment and living beings.
• Burning of fossil fuels like coal, natural gas etc. leads to emission of gases and soot particles in the environment which pollute the air and cause many respiratory diseases.
• Burning of fossil leads to formation carbon monoxide, releases carbon dioxide in the environment which affects the health of living beings.
• Green energy is that energy which does not pollute the environment and are non exhaustible, continuous, sustainable and is renewable in nature.

Thus, it can be said that energy obtained from fossil fuels is not green energy.

• In modern civilization, the technology and development is inevitable. For both of these, continuous energy supply is needed.
• Just like basic needs of human beings, the energy has also become essential.
• We know our day to day life runs on electricity. Equipment like fans, lights, televisions, escalators, vehicles on roads or water supply to our homes, each and everything requires energy
• To obtain the energy in different forms, different sources of energy are utilized.
• Most of the energy used in India is obtained from thermal power, for this energy generation, various fuels are used.
• The coal and fossil fuels are limited. Due to over-exploitation these reserves are getting fast depleted
• Use of fossil fuels is also resulting in pollution and climate change.
• Nuclear energy can be very hazardous.

Lot of research is being done in the field of green energy, but the tremendous human population always is in need of more energy. Therefore, each and every person should save the energy, as saving energy is the need of the hour.

• When many identical Photovoltaic cells connected together forms a solar panel.
• Many such solar panels are connected in series in a form of solar string, the potential difference of individual cells are added and we get required voltage.
• Many such identical solar strings are connected in parallel to get the required current.
• Hence, in this way we get the required amount of energy by connecting solar panels.

Advantages of solar energy:

• Solar energy is green energy i.e. it is renewable and does not cause pollution.
• Solar panels for the generation of electricity requires less maintenance.
• With the help of solar energy, electricity is possible to be generated even in the most remote, inaccessible locations where electric power lines cannot be laid.

Limitations of solar energy: 

• Electricity generation based on solar energy is weather dependent and hence it is less reliable. In winters and in cloudy days, the production becomes less. 
• The whole set-up of the panels requires lot of space to generate considerable amount of electricity. 
• The initial cost of a solar panel is sufficiently high.

• Using the thermal energy released due to burning of coal, steam of very high temperature and pressure is generated. The energy in the steam drives the turbine. 
• 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.

Chemical energy in coal → Thermal energy → Kinetic energy in steam → Kinetic energy in turbine → Electrical energy

• Nuclear power plants consist of nuclear reactors.
• These reactors use uranium rods as fuel and heat is generated by the process of nuclear fission of nuclei of atoms like uranium and plutonium.
• This energy is used to generate the steam of high temperature and high pressure.
• This steam drives the turbines of generators to produce electricity.

The steps of energy conversion are:
Nuclear energy → Thermal energy →Kinetic energy in steam → Kinetic energy in turbine → Electrical energy

• Solar radiation is used to produce thermal energy. For this purpose, many reflectors are used which concentrate the solar radiation on absorbers.
• The heat energy created due to solar radiations is used to make steam.
• The steam possesses kinetic energy.
• This kinetic energy drives turbine and generator.
• The electrical energy is thus created from this kinetic energy.

Thermal energy in radiation → Kinetic energy in steam→ Kinetic energy in turbine → Electrical energy

In hydroelectric power plant, the potential energy in water stored in dam is converted into kinetic energy of water.

• Fast flowing water is brought from the dam to the turbine at the bottom of the dam.
• The kinetic energy of the flowing water drives the turbine.
• The turbine in turn drives the generator to generate electricity.

Potential energy in water→Kinetic energy in flowing water→Kinetic energy in turbine→Electrical energy

Generator works on electromagnetic induction. For this generator must be rotated. Turbine is used to rotate the generator. For rotation of turbine energy is needed. The construction of turbine is different for different types of power plants. This depends on the type of energy source used for driving the turbine. Like in thermal power plants, steam turbine is used whereas in hydro-power plant, water turbine is used.

• Nuclear fission reaction is chain type reaction. If these reactions not controlled properly there can be more production of neutrons in uncontrolled way.
• It will generate enormous amount of heat released during this process will lead to explosion of the plant and cause fatal destruction to environment and mankind.

Thus, it is absolutely necessary to control the fission reaction in nuclear power plants.

Hydroelectric energy, solar energy and wind energy are called renewable energies because they are obtained from water reservoirs, sun and the wind. These energies are inexhaustible, sustainable and abundant in nature and can be regenerated or replenished again and again. These will never extinct even with their excessive use.

Solar photovoltaic cells can be arranged according to the requirement of electric power.

• If power requirement is within mW, use of few number of photovoltaic cells will be able to achieve this much power.
• But, if the requirement of power is in MW, then large number of cells are grouped together to form a solar panel.
• Then, large number of solar panels are connected in series and parallel to get the required electric power.

Thus, it is possible to produce energy from mW to MW using solar photovoltaic cells.

The schematic diagram of solar thermal electric energy generation

• No waste products and harmful gases are released in water bodies and atmosphere when power is generated using hydroelectric power plants.
• Also, water is available in plenty on Earth and is renewable.
• Hence, there is no fear of this energy source dying out. 
• Thus, it has no harmful effects on environment.

All the above facts give an impression that hydroelectric power generation is eco-friendly but it is not.
 

• Many villages and settlements are submerged when a dam and reservoir is constructed.
• The displaced people are given re-settlement, but it causes lot of emotional trauma to people.
• Biodiversity is affected as forest lands is
• The river flow is obstructed by the dam which affects the aquatic organisms residing in such

Thermal energy in radiation → Kinetic energy in steam → Kinetic energy in turbine → Electrical energy

We can obtain a potential difference of 72 V by forming a string of 4 solar panels in series.

Now, to obtain current of 9 A, connect 3 such identical strings in parallel.

The same has been shown below.

• Today electrical energy generation has become the need of the hour. We cannot imagine our life without electricity.
• We have been able to generate electrical energy by various methods. In these methods, a generator is present which works on the principle of electromagnetic induction.
• A turbine is used to rotate this generator and this turbine itself is rotated with the help of an energy source.
• This energy source can be renewable source such as wind, sunlight, nuclear fuels etc. as well as non-renewable source such as coal, petrol, water etc.
• The energy sources such as wind, sunlight have proved to be green sources as they do not pollute the environment and are economical too. But the use of fossil fuel such as natural gas, coal, nuclear energy etc. as energy source has harmful effects on environment.
• The harmful radiations emitted from the nuclear waste has fatal effect on the environment and humans.
• Even the release of soot particles and various greenhouse gases such as carbon dioxide, carbon monoxide on burning or incomplete burning of fossil fuels affects the health of living beings as well as the environment adversely.
• Also, the release of these greenhouse gases is day by day increasing the danger of global warming.
• In order to satisfy ever-increasing demand fr the energy, researcher are working hard on clean energy alternatives.
• We need to as soon as possible find suitable environment friendly substitutes to fossil fuels to save our Earth.