Introduction

Geothermal Energy is the energy obtained from heat stored in the earth crust and used for various purposes like electricity generation or direct heating applications. Geothermal energy is basically stored in earth crust up to depth of 3 to 4 km.

Geothermal Power Plants

Hot water and steam from deep underground can be piped up through underground wells and used to generate electricity in a power plant. Three different types of geothermal power plants exist:

a. Dry steam plants: Hot steam is piped directly from geothermal reservoirs into generators in the power plant. The steam spins turbines, which generate electricity.

b. Flash steam plants: Water that's between 300 and 700 degrees Fahrenheit (148 and 371 degrees Celsius) is brought up through a well. Some of the water turns to steam, which drives the turbines. When the steam cools it condenses back into water and is returned to the ground.

c. Binary cycle plants: Moderately hot geothermal water is passed through a heat exchanger, where its heat is transferred to a liquid (such as isobutene) that boils at a lower temperature than water. When that fluid is heated it turns to steam, which spins the turbines. Binary cycle plant is suitable for India because India is a low geothermal region with low heat enthalpy.

Benefits of Geothermal Energy

• It is a clean fuel as compared to fossil fuel such as oil, gas or coal. A geothermal field emits only 1/6th CO2 as compared to any clean natural gas fired power plant. Binary plants are further less polluter among all geothermal power plants.

• Ground Source Heat Pumps can be a good source of saving money for consumers by reducing electricity bill as it includes only capital cost and maintenance cost is very less.

• The capital cost of geothermal power plant is very high but average units produced per year is very high as compared to other renewable energy resources such as solar, hydro, wind, etc.

• Reinjection/Recycle of Ground Water: Salts and dissolved minerals contained in geothermal fluids are usually re-injected with excess water back into the reservoir at a depth well below groundwater aquifers. This system prolongs the life of the reservoir as it recycles the treated waste water.

• Geothermal Energy (Other than Power) can also be applied in Cold Storage, Tourist Resorts and pools, Melting snow, Poultry & Fish Farming, Mushroom Farming, Horticulture, Greenhouses, Aquaculture, Industrial processes, Space heating, etc.

Geothermal Energy in India

In India, exploration and study of geothermal fields started in 1970. The GSI (Geological Survey of India) has identified 350 geothermal energy locations in the country. The most promising of these is in Puga valley of Ladakh. The estimated potential for geothermal energy in India is about 10000 MW.

The major sites for geothermal energy are:

• Himalayas: J&K, HP and Sikkim; PUGA hot spring in J&K and Manikaran in HP.

• Sohana: Haryana, Rajasthan.

• Son-Narmada-Tapi (SONATA): MP, Chhattisgarh and Jharkhand; Tattapani spring in Chhattisgarh.

• Cambay: Mainly Gujarat and some parts of Rajasthan

• Godavari: AP

• Mahanadi: Orissa, Taptapani Spring in Orissa.

Government Initiatives

• First Geothermal power plant to come in Chhattisgarh by joint cooperation of NTPC and Chhattisgarh Renewable Energy Development Agency (CREDA). Tattapani geothermal field in SONATA geothermal province.

• For Industrial Projects, government has planned to provide capital subsidy of up to 30%.

• Ministry of New and Renewable Energy (MNRE) provides large incentives and subsidies for Research, Design, Development and Demonstration (RDD&D) for harnessing geothermal energy in India.

• Ministry of renewable energy has planned to generate geothermal energy up to 1000 MW by 2022.

• As per Geological Survey of India (GSI), 10000 MW geothermal potential has been identified in India.

More efforts are needed in this direction to realize India's SDGs.