14. Sources of Energy

 14. Sources of Energy  

Characteristics of a Good Fuel

 Energy sources can either be conventional (such as fossil fuel, bio mass, wind and water) or non-conventional (such as ocean energy, geothermal energy, solar energy and nuclear energy). A good source of energy should give higher output per unit volume. Its cost should not be very high. It should be available for a long duration and throughout the year. It should be easy to use and store. The energy produced should be easy to use. 

Characteristics of a Good Energy Source

Characteristics of a Good Energy Source  

Energy sources can either be conventional (such as fossil fuel, bio mass, wind and water) or non-conventional (such as ocean energy, geothermal energy, solar energy and nuclear energy). A good source of energy should give higher output per unit volume. Its cost should not be very high. It should be available for a long duration and throughout the year. It should be easy to use and store. The energy produced should be easy to use.  

Fossil Fuels 

 With increasing industrialization and improvement in quality of life, the demand for energy continues to grow. Due to this, fossil fuels such as coal, petroleum and natural gas are the most exploited source of energy. Here are some of the benefits of using fossil fuels:

Fossil fuels are easily available

They are easily combustible so can even be used for household consumption

They have high calorific value in comparison to wood

Cost effective – Due to low installation cost, the overall cost of producing electricity from fossil fuels is less than hydroelectric, solar, nuclear and other forms of electricity generation

Oils and gases are easily transported through pipes while coal can be transported through railways

However, there are several drawbacks of using fossil fuels, as mentioned below:

Burning fossil fuels releases carbon dioxide. As carbon dioxide is a greenhouse gas, it is responsible for global warming

Sulphur and nitrogen present in fossil fuels form their oxides during combustion. These oxides react with rain water to cause acid rain.

Coal-mining leads to large-scale deforestation and affects other dependent life-forms

Petroleum spills in the ocean cause pollution of water and air and the death of aquatic living organisms

Working of a Thermal Power Plant  

Thermal power plants use coal for producing electricity. In any thermal power plant, powdered charcoal is fed to the furnace through a conveyor belt. Heat released from the furnace is used to heat water to form steam. This high pressure steam runs the turbines, converting kinetic energy to mechanical energy. An electric generator converts mechanical energy to electrical energy. Electrical energy produced reaches consumers through transmission cables.

Hydel Power Plant – Benefits and Limitations 

 A hydel power plant uses the energy from water stored in dams to produce electricity.

A reservoir is built on a river to store water. Water from the reservoir falls from a height and runs the turbines. The electric generators attached to the turbines convert mechanical energy to electrical energy.

There are several benefits of using water to produce electricity. These are mentioned below:

Electricity production is not dependent on day or night

Dams do not consume any water. Water is released and can be used downstream after production of electricity.

There is no waste byproduct from a hydroelectric plant

Dams collect water, which can be released for use when required

Once constructed, dams last for many years.

There is no pollution of air or water

Some of the limitations of using hydel power are the mentioned below:

Construction of dams and hydroelectric plants is expensive and takes time

Dams can cause flooding upstream or downstream and lead to soil erosion

When a dam is created, downstream areas have less access to water than usual, which could lead to water scarcity

Water stored in a dam is cool. When released, it can affect the aquatic animals downstream from the dam, which are used to warmer water.

Wind Energy - Benefits and Limitations

  Energy from the wind is harnessed by using windmills. A windmill is a tall tower with three rotor blades and a box called a “nacelle” fitted on the top. The nacelle is attached in such a way that it can turn the windmill to ensure the rotor blades face the wind and capture maximum energy.

The blades rotate due to the kinetic energy of the wind. The blades are attached to a gear box inside the nacelle via a shaft. The gears increase the rotation speed and power a generator. The generator converts mechanical energy to electrical energy. Electrical energy is transmitted to homes through a power cable.

Here are some of the benefits of harnessing energy from wind:

It neither pollutes air, water or land, nor produces any waste.

Wind mills can be installed in a wide variety of places like plains, coastal areas and oceans.

The process of converting wind energy to electrical energy can happen throughout the day or night, whenever wind is available.

The limitations of using wind to produce electricity are:

The amount of electricity produced is not constant or continuous and cannot be predicted, as it is dependent on the wind.

Wind mills can harm birds and disturb the biodiversity of the region.

Energy from Biomass

  Energy from Biomass  

Biomass includes agricultural waste (residue left after the crop is harvested), cattle dung and kitchen waste. Energy stored in biomass is harnessed through biogas plants.

A deep pit is dug to install a biogas plant. The digester is built inside this pit with bricks and covered with a dome. Slurry of biomass is fed into the digester. In the digester, the slurry decomposes in the absence of oxygen in a few days and gases like methane, hydrogen and hydrogen sulphide are released. The gases released get collected in the gas chamber. A valve controls the outflow of bio-gas.

Benefits of using biomass as a source of energy are mentioned below:

It is a renewable source of energy as it is created from plants and animal waste.

It comprises 75% methane and burns without smoke or ash.

A by-product is excellent manure.

When sewage and farm waste is utilized to produce energy on a large scale, it is also a safe and efficient method of disposing waste.

The cost of producing energy is much less than fossil fuels.

The demerit of using biomass is that biogas burns to form carbon dioxide which leads to global warming, though in smaller amounts than fossil fuels.

Working of a Solar Geyser  

Solar geysers are generally used for heating water for domestic consumption.

A solar geyser typically has an inclined tank placed on a roof top. Water is fed into the geyser from an overhead reservoir. Water in the geyser tank passes through long copper pipes exposed to sunlight and gets heated. Hot water gets collected in the tank and the pipes get filled with cold water. Hot water from the tank flows through the pipes to the tap while cold water from the reservoir enters the geyser and goes through the heating process.

Working of a Solar Cooker  

A typical solar cooker is an insulated box with a black interior coating. The interior coating has no sharp edges to ensure that sunlight is reflected inside the box. The cover of the box is made of glass to retain heat as happens in the case of a green house. A glass reflector faces the sun directly, reflecting the sunlight inside the box to heat the vessel inside faster.The food to be cooked is kept in a black vessel which is put inside the box. When the box is left in the sun, its temperature rises and the food gets cooked slowly.

Benefits and Limitations of Using Solar Energy 

 Solar energy is converted to electrical energy using solar panels. These panels are placed on a roof-top or in open areas where ample sunlight is available. The electricity produced by the panels flows through an inverter which converts it to usable form.

The benefits of using solar energy are:

Sunlight is free and readily available on most of the earth.

It is indefinitely renewable.

Solar panels can be placed in remote and inaccessible areas too.

Solar energy does not produce any waste or pollutant.

Once installed, solar panels require very little maintenance.

Solar panels do not make any noise.

The limitations of using solar energy are mentioned below:

High installation and initial cost

Limited availability - the process only works during the day and on sunny days, but not on cloudy or rainy days

The panels need a large area.

Special grade silicon required to make solar cells is limited in nature.

Solar panels are made of harmful substances like silicon, lead, mercury and cadmium. Their production and disposal can lead to pollution of air, water and soil.

Energy from Tides and Waves 

 Energy from the sea is harnessed from areas which regularly see tides or waves. In a narrow area in the sea which sees a lot of tides regularly, dams are constructed. Turbines are fitted at the opening of the dams.

Alternately, the nacelle and the rotor blades are attached to a strong foundation structure underwater. The tides or waves rotate the rotor blades. The rotor blades of the underwater turbine spin as the tides ebb and flow.

The rotor is connected to the gear box via a shaft. The gears turn and drive the electric generator. The generator converts the mechanical energy to electrical energy. Underwater cables carry electrical energy for consumption.

Here are some of the benefits of harnessing energy from waves and tides:

A sustainable source of electricity

Involves no fuel and there is no emission of greenhouse gases

Does not lead to any kind of pollution

Produces much more electricity than a windmill

Has low cost of production of electricity

The limitations in harnessing energy from the sea are:

High installation cost

The process can disturb the ecology of the oceans

Parts corrode frequently and maintenance is difficult

Harnessing Ocean Thermal Energy

Harnessing Ocean Thermal Energy  

There is a difference in the temperature of ocean water at the surface and deep below. This difference in temperature is used to produce electrical energy.

Hot water from the surface of the ocean is used to boil liquids such as ammonia which have a low boiling point. The steam of ammonia spins the turbine to generate electricity, which is transmitted through an underwater cable. Cold water from deeper in the ocean is pumped up to cool down and convert the ammonia gas back to liquid ammonia.

Harnessing Geothermal Energy

The earth’s crust has some hot spots or pockets due to trapped molten rocks. Heat from these hot spots turns underground water into steam or hot springs. In such areas, wells are drilled 5,000-10,000 feet deep in the earth’s crust and superheated fluids or steam emerge from them. Superheated fluids heat water in a flash tank and convert it to steam. The steam from the tank is directed to spin a turbine. The turbine is connected to the generator through a shaft. The generator converts the mechanical energy to electrical energy. Electricity flows to the transformer, from which a cable transmits it to consumers. After rotating the turbine, water is directed to the flash tank. The superheated fluids that came out of the well cool and are injected back into the well.

The benefits of converting geothermal energy to electrical energy are mentioned below:

The cost of running a power plant is low

No fuel is involved

No emission of greenhouse gases

Electricity can be produced 24/7

Does not lead to any kind of pollution

However, there are certain limitations in using geothermal energy. These are:

Power stations can only be set up at a few locations.

The cost of setting-up a power plant is high

It is difficult to drill hot rocks

Some harmful gases from within the earth can escape into the atmosphere from the drilled holes

Harnessing Nuclear Energy  

Nuclear power plants convert energy released during nuclear fission to electrical energy.

In a nuclear reactor, pellets of uranium, thorium or plutonium oxide are used as fuel. Control rods made from boron or cadmium are used to keep the reaction under control.

Before the reaction begins, the control rods are pulled out of the reactor. A thermal neutron initiates a chain reaction inside the reactor. Water inside the reactor acts as a moderator and slows down the speed of the neutrons being released in the reaction. As the reaction occurs, a lot of thermal energy is released. Due to this thermal energy, the water inside the reactor gets superheated but does not evaporate due to high pressure. The superheated water flows in such a manner that it heats water in the second loop, turning it into steam. The steam spins the turbine which is attached to an electric generator and electricity is produced.

The control rods that were pulled out initially are inserted in the reactor to absorb undesired neutrons and stop the reaction.

The benefits of harnessing nuclear energy are:

A nuclear power plant does not require a lot of space, release carbon dioxide or pollute air

Electricity can be produced at all times through the year

Output can be controlled, depending on the need

The amount of energy produced by a nuclear power plant is much higher than from other sources

There are certain limitations in harnessing nuclear energy:

Construction of a nuclear power plant is expensive

Nuclear waste emits harmful radiation. It should be disposed of in a way that does not pollute the environment.

The reactor requires a large amount of water for cooling so the power plant needs to be built near a large body of water

Meltdown of nuclear power plants caused the Chernobyl and Fukushima disasters