Geothermal energy is the energy derived from beneath the earth’s crust. The interior of the earth is divided into three main regions-crust, mantle and core.  The crust is in solid state and we live on it. The inner regions are very hot with the temperature reaching around 6000^o F at the core region. The heat from this region is transferred to the above lying rocks. When any water passes through these hot rocks, it is heated up. The heat from this water can be harnessed as geothermal energy. Generally the areas with active earthquake and volcanoes are rich in geothermal energy.

How geothermal are harnessed:
Basically, the geothermal energy is harnessed by drilling a pipe in the suitable region i.e. those regions which have hot rocks of suitable temperature. Cold water is passed through this pipe to the hot rocky regions. The high temperature of the rocks heats up the water which is then brought up to the surface and made to rotate the turbine of a generator to produce electricity. It can be done in three different ways:

1. Dry steam technology
2. Flash technology
3. Binary technology

Dry steam technology: It is the oldest method of harnessing geothermal energy and can be harnessed when the temperature of water is around 150^oC. In this method, the underground steams which escape to the outer surface through the cracks in the earth’s crust directly rotate the turbine of the generator and produce electricity. It is made to pass through a rock catcher before reaching the turbine. The rock catchers provide safety to the turbine from the rocks which comes to the surface along with the steam.

Flash technology: It is the most commonly used method and are employed when the temperature of the water is 180^oC or above. Here, the hot underground water comes up to the surface due to its high pressure and is collected in a low pressure tank. The sudden change in the pressure changes the water into steam which is then made to rotate the turbine of the generator. Some steam and gases might escape from such plants.

Binary technology: This method can be employed when the temperature of the underground water is as low as 57^o C. The hot water is brought up to the surface of the earth’s crust and is used to heat up another ‘working fluid’ kept in an adjacent tank. The working fluid has much lower boiling point than the water. So, when heat is exchanged from the hot water to the fluid through a device called heat exchanger, the fluid vaporizes. It is then used for rotating the turbine of the generator. This method is not so widely employed at present due to its lower efficiency.

Advantages of geothermal energy:
Some of the advantages of geothermal energy areas under:

1. It is an inexhaustible source of energy. With proper management energy can be harnessed effeciently for a long time from the same source.
2. Unlike wind energy or solar energy, geothermal energy is not affected by the meteorological condition of a place or by the season. It can be harnessed at any time of the year or the day.
3. The space needed to install the geothermal plant is also very less as compared to the installation of nuclear plant, coal plant or solar plant etc.
4. Another advantage of the geothermal energy is that it produces less air pollution as compared to other sources of energy.
5. Hot water from inside the earth’s crust can also be used as a source of hot bath or spas. In fact many such hot baths are said to have the healing properties for various skin diseases.

Disadvantages of geothermal energy:
Geothermal energy has also certain disadvantages. Some of which are mentioned below:

1. Its distribution is limited to certain geographical areas many of which are not feasible for harnessing. For instance, the geothermal energy at regions near the poles or at high altitude regions cannot be harnessed efficiently.
2. Another disadvantage is its cost. The exploration for regions rich in geothermal energy can prove to be expensive.
3. People are also concern about the gases and other toxic minerals (like boron and arsenic etc) that may be brought up to the surface along with the hot water or steam. Geothermal power plant often releases the foul smelling hydrogen sulphide gas.  The toxic minerals which comes up if not disposed off properly could pollute the water bodies.
4. Installation of the geothermal plant can be risky for the investors. Sometimes, an active geothermal plant can run out of the steam due to various reasons such as improperly harnessing the energy, disturbance by the occurrence of the earthquakes etc.

• Written by jabeen.
• In category General Reference.
• 12 years ago.

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