Geothermal Energy – Earth’s Own Green Energy

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Geothermal originated from a Greek word where, geo means earth and thermal means heat. Geothermal energy is defined as the heat discharged from underneath the surface of the earth, which is formed by radioactive decay of materials. Geothermal energy is a green and renewable energy source. It is not hazardous to living organisms and is protective towards human and environmental health. Apart from providing hot water throughout the year, geothermal energy can be used to keep houses warm in winters and cool in summers with zero water requirements and reducing electricity bills. The steam and hot water present in underground reservoirs can be tapped to generate electricity and also to heat and cool buildings directly. In the USA, geothermal water is being used to heat homes, offices, for growing plants in greenhouses and in the sidewalks of roads to melt snow.

From prehistoric to current era people are making use of geothermal energy. The energy reaches the earth’s surface in the form of geothermal hot springs, which is used for recreational and medicinal bathing purposes. In China, during the Qin dynasty in the 3rd century, the oldest known pool was created for this purpose. Even today such pools continue to be a relaxing factor for vacationers. The water in this area is warm because it comes in contact with rocks heated by magma below the earth’s surface. In 20th century, people started using geothermal energy for electricity generation and as a supplement to oil, natural gas, coal, and nuclear power sources. For the electricity production, deep wells are drilled into the underground reservoirs to tap steam and hot water to power the turbines linked to electricity generators.

The first geothermal generated electricity was produced in 1904, in Larderello, Italy. There are three types of geothermal power plants: dry steam, flash and binary plant. Dry steam is the oldest geothermal technology, which makes use of steam directly to drive turbines. Flash plants pull deep high pressure hot water into coolers, low pressure water resulting in steam is used to drive turbine. Binary plants use the passage of hot water by a secondary fluid with a lower boiling point than water thus causing secondary fluid to turn to vapour which drives a turbine. Over 20 countries are using geothermal energy, and the USA is the world’s largest producer. Many of the building and swimming pools in Iceland are heated using geothermal hot water.

Smart or green buildings are designed to conserve energy by using the geothermal energy. The heat hidden within the earth is moved to houses and offices for heating and cooling purposes. The heat hidden below the frost line always will be around 10°C which is due to 46% of sun energy that is absorbed and stored in the form of geothermal energy. Geothermal heating and cooling system has three main components: heat-pump unit, liquid heat-exchange medium and air-delivery system. There exist three types of loop systems viz., vertical (U shaped pipe; equal or >300 feet), horizontal (6-10 feet deep) and open loop system (75-100 feet deep). These systems require little maintenance when installed properly and the buried loop can last for generations. Future homes can use this concept to save environment and money. It is more efficient and cost effective than burning fossil fuels, and reduces our dependence on expensive oil sources. Geothermal energy will be more beneficial to residential/commercial buildings as it does not require additional space and water requirement but reduces CO2, pollution, waste generation and weather atrocities such as droughts and floods. 

Author: Manupati Hemalatha, PhD Scholar,  Bioengineering and Environmental Sciences Lab, EEFF Department, CSIR-Indian Institute of Chemical Technology (CSIR-IICT), Hyderabad.