Towards Green Energy

 Energy and uses of energy

    Energy is a primary need along with food, cloth and shelter. We need energy in different forms for     different type of works.

·                                                                   The energy may be in the form of mechanical energy, chemical energy, sound energy, heat energy and light energy etc.

   Green energy :-

                                 The eco-friendly form of energy which do not cause environmental problems and are non- exhaustible, perpetual and sustainable is called as green energy.

      Examples- Hydroelectric energy, wind energy, solar energy, tidal energy, energy obtained from biofuels etc.

                    These sources of energy do not produce toxic gases or other pollutants therefore they are safe.

Generation of electrical energy

                                                  Most of the electric power plants are based on the electromagnetic induction.   

       According to this principle, whenever magnetic field around a conductor changes, a potential difference is  

       generated  across the conductor. The field around the conductor can be changed by two ways.

                        1. If a conductor is stationary and magnet is rotating.

                        2. If a magnet is stationary and conductor is rotating.

               In both these cases, electric current is induced in the conductor.

v  Large generators are used in commercial power plants.

v  Turbine is used to rotate the magnet in the generator.

v  A turbine has blades. When a flow of liquid or gas is directed on the blades, it rotates due to the kinetic energy of the flow.

v  This turbine is connected to electric generator. Hence, the magnet in the generator rotates and electricity is generated.

v   

                                                   Thermal energy based electric power station

v  In thermal power plant the turbines are rotated using steam.

v  Coal is used to generate a steam of very high temperature and pressure.

v  The kinetic energy in the steam rotates the turbines. The rotation of turbines produces its own mechanical kinetic energy.

v  The generator connected to the turbine rotate an electrical energy is produced.

v  The steam is condensed in the condenser and converted back into water and the water is re-circulated to the boiler.

v  In thermal power plants, thermal energy is converted into kinetic energy. Kinetic energy is converted into mechanical energy and mechanical energy is converted into electrical energy.

                                                

                                    

                                 Problems associated with thermal power plants

v  Due to the burning of coal the mission of carbon dioxide, Sulphur dioxide nitrogen dioxide and carbon monoxide takes place. These gases are harmful to the health.

v  Shoot particles emitted during combustion causes respiratory problems such as asthma.

v  The coal reserves in the world are limited. So in the future there will be limitations on the availability of the coal.

                                                                Nuclear power plants

v  In nuclear power plants, the energy is released by fission of atoms like uranium and plutonium.

v  This energy is used to generate a steam of very high temperature and pressure.

v  The kinetic energy in the steam rotates the turbine.

v  The turbine rotates the generator to produce electrical energy.

                                                      Formation of nuclear energy

v  When the neutron is bombarded on atom of U – 235, it absorbs the neutron and convert into isotope U – 236.

v  U-236 is extremely unstable and converts into atoms of barium and krypton through a process of fission releasing three neutrons and 200 MeV energy.

v  These three neutrons cause fission of the other U-235 atoms releasing more energy.

v  This process of fission of U - 235 atoms is continuous and is called as chain reaction.

                                       

Advantages of nuclear power plants

v  It does not use fossil fuel like coal.

v  It does not cause air pollution.

v  If sufficient nuclear fuel is available, it can be a good source of electrical energy.

Problems associated with nuclear power plant

v  The disposal of nuclear waste is a big challenge before the scientists.

v  An accident in nuclear power plant can be very fatal.

v  The accident in nuclear power plant may result in release of very harmful radiations.

[Nuclear power plants in India are as follows:- Tarapur, kundakulam, BARC (Bhabha atomic research centre), Narora, Ravatabhata]

                                                                     

                              Natural Gas Power plant

v  In this power plant, the turbine is run by a gas at a very high temperature and pressure generated by combustion of natural gas.

v  In this plant there are three main sections as compressor, combustion chamber and turbine.

v  Pressurized air is introduced into the combustion chamber using a compressor.

v  In the combustion chamber, the natural gas burns in the presence of air.

v  The gas at very high temperature and pressure generated in this chamber runs the turbine. The turbine then drives the generator to produce electricity.

                                                      Advantages of natural Gas Power plant

ü  It is more efficient than thermal power plant.

ü  It causes less pollution because there is no sulphur  in natural gas.

                                 Electric energy generation using solar energy

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

v  Using radiation from sunlight without using a transformer, it is trapped directly into solar photovoltaic cells. The solar energy is directly converted into electrical energy in photovoltaic cells.

v  Solar energy is converted into thermal energy and later by driving turbine generator - system the thermal energy is converted into electricity.

       1. Solar photovoltaic cell

v  Solar photovoltaic effect is the conversion of solar energy directly into electrical energy. Such generated energy is DC (direct current) in nature.

v  The solar cells are made up of silicon.

v  A silicon solar cell of dimension 1 cm² generates a current of 30 mA (milliampere) and potential difference of about 0.5 volt.

v  Therefore a silicon solar cell of dimension 100 cm² generates about 3 ampere current and potential difference of about 0.5 volt.

v  The potential difference available from a solar cell is independent of its area.

1. Solar cells connected in series

v  When two solar cells are connected in series, the potential difference after 10 from both the cells is the sum of the potential difference of individual solar cells.

                                                             V = V₁ + V₂

v  The current generated from combination in series is equal to the current from an and individual cells.

                                                              I = I₁= I₂

v  In this combination, current from the individual cells cannot be added.

   2. Solar cells connected in parallel

v  When two solar cells are connected in parallel, the potential difference obtained from this combination is equal to the potential difference of each cell.

                                                               V = V₁ = V₂

v  The potential difference cannot be added when the combination is in parallel.

v  The current generated from the two cells in parallel is the summation of the current from individual cells.  I = I₁ + I₂

Solar panel :-

v  Solar panels are formed by connecting many solar cells in series and in parallel combination.

v  Desired potential difference and current can be obtained by making solar panels by connecting solar cells in series and in parallel.

v  The DC power is available from the solar cells. So, it can be used for LED lights and other appliances that work   on DC power.

v  Most of the domestic appliances run on AC power.

v  Therefore, DC solar power is converted to AC power with the help of inverter.

v  Solar energy is available only in the presence of sunlight; therefore it is stored in batteries for later use.

Advantages of solar energy:-

v  It does not cause any pollution.

v  Electricity is generated without any fuel combustion.

v  It is eco-friendly, green energy.

v  The technology can be completely utilized in regions with abundant sunlight.

Limitations of solar energy:-

v  Solar energy is only available during daytime.

v  The production of electric energy is affected by cloudy weather.

v  The power present in the solar cells is DC while most of the domestic equipments work on AC.

 Solar thermal power plant:-

v  Solar radiations are used to produce thermal energy.

v  For this purpose, many reflectors are used which concentrate the solar radiation on absorbers.

v  The heat energy created due to solar radiations is used to make steam.

v  The kinetic energy of steam drives turbines and generator.

v  The generator produces electrical energy.

How to get the required amount of energy by connecting solar panels?

v  The photovoltaic solar cells can be connected in series or in parallel to make a solar panel.

v  When solar cells are connected in parallel, the currents of the individual cells are added in the combination, but the potential differences from individual cells are not added.

v  When solar cells are connected in parallel, the currents of the individual cells are added in the combination, but the potential differences from individual cells are not added.

v  Through such connections the required potential difference and current can be obtained.

v  To get required current, many solar panels are connected in series and in parallel.

v  When many solar panels connected in series there for me a solar string.

v  Many solar strings connected in parallel make a solar array. In such manner we can get the required amount of energy by connecting solar panels.

Electric energy generation and environment:-

v  Electricity generation based on fossil fuels like coal, natural gas & nuclear fuels are not environment friendly.

v  If such energy sources are used, they can cause harm to the environment.

v  The incomplete combustion of fossil fuels causes release of carbon monoxide.

v  The carbon dioxide produced through all the combustion is creating global warming.

v  The nitrogen dioxide released through burning is responsible for acid rain.

v  The reserves of fossil fuels are limited. They are going to deplete in future.

v  In production of Nuclear energy, there is a great risk of accidents. The safe disposal of nuclear waste is also a problem.

v  In order to generate more electric energy, we must use renewable sources of energy for production of

             electricity.

Hydroelectric power plant:-

v  In hydroelectric power plant the water stored in the reservoir is used as a source of potential energy.

v  This water is made to fall at a great speed and hence there is a production of kinetic energy in flowing water.

v  This fast flowing water falling down from the reservoir is brought to the turbine at the lower levels.

v  The kinetic energy of the flowing water drives the turbine.

v  The turbine in turn drives The generator to generate electricity.

Advantages of hydroelectric power generation:-

v  In hydroelectric power generation there is no combustion of fuel so there is no pollution.

v  Electricity can be generated when required

v  Water supply can also be achieved due to dam.

v  Rains replenish the store is aware of the water.

Problems with hydroelectric power generation:-

v  The backwater of dam may submerge villages or towns in that area.

v  This leads to the problem of rehabilitation of the displaced population.

v  This can also submerge forest as well as fertile land.

v  Obstruction of the flowing water leads to adverse effect on the living world in the aquatic system.

Electricity generation using wind energy:-

v  The kinetic energy of wind can be converted to electrical energy with the help of wind turbine.

v  Such kinetic energy of wind was used for lifting of water, for driving flour mill, etc. In olden Times.

v  When the wind strikes the blades of the turbine, the blades rotate.

v  The axle of the turbine and electric generator are connected through a gearbox which increases the rotations per unit time.

v  The rotating blades drive the turbine which in turn drives the generator and produces electricity.

v  From less than 1 kW to about 7 MW is the range in which wind turbines can produce electricity.