Towards Green Energy Science Notes

Towards Green Energy Science Notes

Important Points :

• The capacity to do work is called energy.
• Potential energy and kinetic energy are the two types of energy.
• Heat, light, electric energy, solar energy, chemical energy, nuclear energy, mechanical energy, etc. are different forms of energy.

Energy and use of energy :

→ Energy is a very basic and primary need. For various types of work, energy is needed in different forms. E.g. Mechanical energy, chemical energy, sound energy, light energy or heat energy.

→ Energy can be converted from one form to another by transformations. This fact is used by man to satisfy his energy needs.

→ We use electric energy in various appliances such as bulbs and tubelights. Fans, iron, refrigerator, water pumps, cellphone chargers, television sets, tape recorders and computers.

→ Electric energy is produced in the generators. By using the principle of electromagnetic induction, the magnetic field around conducting wires is changed and this creates the potential difference. This results in the formation of electric energy.

Generation of electrical energy :

Production of electricity :

• 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.
  • Keeping the conductor stationary and rotating the magnet.
  • Keeping the magnet stationary and changing the field around the conductor.
• In both cases there is creation of potential difference across the conductor.
• The electric generators are based on this principle. They generate the electrical power.
• In commercial power generation plants → Large generators Turbine having blades rotates the magnet Flow of liquid or gas is directed on the turbine blades → The kinetic energy in the flow Rotates the magnets in the electric generator Electric energy is produced.
• 
• There are different types of power generating stations depending upon the type of energy source that is used to rotate the turbine.

Thermal energy based electric power station :

→ In thermal energy power plants the steam is used to rotate turbines. Coal is burnt Heat energy given to water Water heated in a boiler → Water converted into steam of very high temperature and pressure → Steam in energy used to rotate turbines Generator connected to turbines Electric energy produced. 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

→ The atoms and molecules present in the coal are formed due to chemical bonds. The energy is stored in chemical bonds. When the coal is burnt, this energy is released.

→ The chemical energy in coal is transformed into thermal energy When water is heated, it converts into steam. This steam in under high pressure and temperature. This force of steam rotates the turbines. The same steam is again condensed and converted back into water. The excess heat in turbine again makes this water turn into steam. In this way turbine rotates very effectively due to steam.

Schematics of thermal power plant :

• Thermal power plant has two types of towers.
• In the power station, boiler, turbine, generator and the condenser are arranged.
• In the boiler, combustion of coal takes place. Gases produced are released in the atmosphere through very high chimney.
• Turbine is rotated by steam at high temperature and high pressure.
• The temperature and pressure of steam later decreases. This steam is then condensed to water by cooling it, in condensers.
• Condensation of the steam takes place due to transfer of heat energy in the steam to the water.
• The heat absorbed by the water is then released to atmosphere through vapour and heated air through cooling tower.
• Most of the electricity generation is done through thermal power plants in India. But there are certain problems in such electricity production.

Problems caused due to thermal power plants :

• Gases like carbon dioxide, sulphur dioxide and nitrogen oxide, etc. soot particles are released due to such burning of coal causing air pollution. This causes serious health problems.
• Especially the respiratory system is affected.
• The coal reserves are limited and exhaustible, Hence there would be problems about its availability.

Power plant based on Nuclear Energy :

→ The energy released by fission of nuclei of Uranium or Plutonium atoms is used to generate the steam of high temperature and high pressure, which is used to rotate the generator for production of electricity.

→ 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.

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 liberates the energy which is known as nuclear energy or atomic 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	Problems of nuclear energy
Fossil fuel like coal is not used in a nuclear power plant. Hence air pollution does not occur.	Radioactive and harmful radiations are emitted after fission of nuclei occurs.
If sufficient nuclear fuel is available, it becomes a good source of electrical energy.	The nuclear waste requires very safe disposal.
–	Very fatal accidents can happen in power plant which emits very harmful radiations.

Power generation plant based on energy of natural gas :

Very high temperature and pressure generated by combustion of natural gas. This gas is used to run the turbine.

In power generation plant based on energy of natural gas three main sections are present.

• Compressor
• Combustion chamber
• Turbine

→ Into the combustion chamber pressurised 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.

Advantages of power generation plant, using natural gas :

• More efficiency than coal power plants
• Less polluting as there is no sulphur in natural gas. Less pollution by burning of natural gas.
• Use of energy is unavoidable in our daily life but controlled and careful use is essential.

Electric energy generation and environment :

→ 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 → Carbon monoxide → Adverse effects on health
• Burning of fossil fuels like coal, and natural gas → Emission of toxic gases and soot particles → Air pollution → Problems in respiratory system, like asthma
• Burning of fuels → Increase in percentage of carbon dioxide in the air → Global warming and climate change
• Burning of fuels like coal, diesel, petrol, etc. → Nitrogen dioxide → acid-rain

Non-renewable nature :

• 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 for 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 a difficult problem. Accident in nuclear power plant can be highly disastrous.

Towards the eco-friendly green energy :

Green energy is that energy in which there is no pollution during the generation.

• 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
• Flowing water → Kinetic energy + Water reservoir → Potential energy.
• 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 generator electricity is generated.

Advantages of hydroelectric power generation	Problems with hydroelectric power generation
Since there is no combustion, there is no pollution.	Some villages or settlements are submerged.
Possible to generate electricity as and when required.	People are displaced and their rehabilitation is the major problem.
Water supply can also be achieved due to dam.	Fertile land, agricultural plots forests and biodiversity is lost forever.
Rains replenish the stored reservoir of the water.	Obstruction of the flowing water lead& 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

→ Wind turbines can produce electricity from less than 1 kW to about 7 MW (7000 kW). The installation of windmills to produce electricity from wind energy depends upon following factors:

• The wind velocity available at the site of installation,
• Geographical factors.

→ Appropriate for installation of wind turbines are done at a particular place. Seashore is most suitable place for installations as here the wind velocity is more. Wind-energy is a clean energy source but due to wind velocity problems its use is limited.

Electric Energy generation using solar energy :

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

• Solar radiations are trapped directly into solar photovoltaic cells without using any transformer. Electrical energy is produced from solar energy due to direct conversion occurring in photovoltaic cells.
• Initially solar energy is converted into thermal energy and later electricity is generated from thermal energy by driving turbine generator system.

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.
• If a silicon solar cell’s dimension = 1 cm²
  Then current = 30 mA and potential difference = 0.5 V.
• Therefore, a silicon solar cell of dimension = 100 cm will generate about 30 mA/cm² × 100 cm² = 3000 mA = 3 A current and 0.5 V.
• The potential difference available from a solar cell is independent of its area.

Connections of solar cells :

→ Solar cells connected in series :

→ Solar cells connected in parallel :

Solar cells in series	Solar cells in parallel
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.	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 current generated from combination in series is equal to the current from an individual cell.	The potential differences cannot be added when the combination is in parallel.
When solar cells are connected in series, currents from the individual cells cannot be added.	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.
• Desired 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 electrie 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.

Science Notes