Geothermal power is generated from underground heat. Geothermal energy is heat derived within the sub-surface of the earth. Water and/or steam carry the geothermal energy to the Earth’s surface. It is found around the globe and available year-round, this largely untapped renewable energy source offers the advantage of steady, predictable large-scale power generation, in comparison to the higher variability of solar and wind power. Geothermal Energy is a mature renewable energy technology that has a potential to provide clean and reliable energy for power generation and direct heating & cooling.

Geothermal Energy can be utilized for both electric power production and direct heat applications including Ground Source Heat Pump (GSHP) for space or district heating, generating hot water for domestic/ industrial use, running cold storages and greenhouse, horticulture, etc. However, Geothermal Energy has experienced modest growth worldwide in recent times as compared to other RE sources especially wind or solar due to its site specific nature, risk/uncertainty involved with resource exploration and high capital cost.

Geothermal Energy: World Scenario

This key renewable source covers a significant share of electricity demand in countries like Iceland, El Salvador, New Zealand, Kenya, and Philippines and more than 90% of heating demand in Iceland. Total Installed Capacity for Geothermal Power is around 13.5 GW. Leading countries in geothermal power generation capacity are USA (3600 MW), Philippines (1900 MW), Indonesia (1600 MW), New Zealand (1000 MW), Mexico (900MW), Italy (800 MW), Turkey (800 MW), Iceland (700 MW), Kenya (600 MW) & Japan (500 MW).

Total installed capacity for geothermal direct heat utilization for heating/ cooling (excluding heat pumps) is around 23 GWth. leading countries in geothermal direct heat use are China (6.1 GWth ), Turkey (2.9 GWth), Japan (2.1 GWth), Iceland (2.0 GWth) & Italy (1.4 GWth). Total installed capacity for Ground Source Heat Pump (GSHP) is around 50.3 GWth with leading markets as USA, China & Europe (France, Germany, Italy & Sweden).

Geothermal Energy Indian Scenario

India is still at nascent stage of geothermal energy utilization with no geothermal power plant set up in the country so far due to high upfront cost of Rs 30 Cr/ MW & indicative Tariff in range of Rs 10 per KWh, site specific deployment, lack of load center and power evacuation facility nearby, high risk involved in exploration, etc. Geological Survey of India (GSI) with CSIR – National Geophysical Research Institute (NGRI) carried out preliminary resource assessment for the exploration and utilization of geothermal resources in 1970s & 1980s in the country.

As per preliminary investigations undertaken by the GSI, there are around 300 geothermal hot springs in India. Most of these geothermal hot springs are in medium potential (100 C to 200 C) and low potential (<100 C) zones. The promising geothermal sites for electric power generation are Puga Valley & Chummathang in Jammu & Kashmir, Cambay in Gujarat, Tattapani in Chattisgarh, Khammam in Telangana & Ratnagiri in Maharasthra. The promising geothermal sites for direct heat use applications are Rajgir in Bihar, Manikaran in Himachal Pradesh, Surajkund in Jharkhand, , Tapoban in Uttarakhand & Sohana region in Haryana.

Technologies of Geothermal Energy

Power Generation: Hot water and steam from deep underground can be piped up through underground wells and used to generate electricity in a power plant. There are three types of geothermal power plants:

• Dry Steam Plants which use geothermal steam directly. Dry steam power plants use very hot (>235 °C) steam from the geothermal reservoir. The steam goes directly through a pipe to a turbine to spin a generator that produces electricity.
• Flash Steam Plants which use high pressure hot water to produce steam. Flash steam power plants use hot water (>182 ºC) from the geothermal reservoir. When the water is pumped to the generator, it is released from the pressure of the deep reservoir. The sudden drop in pressure causes some of the water to vaporize to steam, which spins a turbine to generate electricity. Hot water not flashed into steam is returned to the geothermal reservoir through injection wells.
• Binary Cycle Plants which use moderate-temperature water (107 to 182 ºC) from the geothermal reservoir. In binary systems, hot geothermal fluids are passed through one side of a heat exchanger to heat a working fluid in a separate adjacent pipe. The working fluid, usually an organic compound with a low boiling point such as Iso-butane or Iso-pentane, is vaporized and passed through a turbine to generate electricity.

Other thermal applications:

Apart from geothermal power generation, this renewable source can be utilized directly for thermal applications through these technologies:

i) Space/District Heating: In areas where hot springs or geothermal reservoirs are near the Earth’s surface, hot water can be piped in directly to heat homes or office buildings. Geothermal water is pumped through a heat exchanger, which transfers the heat from the water into the building’s heating system. The used water is injected back down a well into the reservoirto be reheated and used again.

ii) Geothermal Heat Pump/Ground Source Heat Pumps: A few feet under the ground, the soil or water remain a constant 50 to 60 degrees Fahrenheit (10-15 degrees Celsius) year-round.In this method, geothermal heat pumps use a system of buried pipes linked to a heat exchanger and ductwork into buildings. In winter the relatively warm earth transfers heat into the buildings and in summer the buildings transfer heat to the ground or uses some of it to heat water. These heat pumps function as both air-conditioning and heating systems.Fluid circulates through a series of pipes under the ground or beneath the water of a pond or lake and into a building.An electric compressor and heat exchanger pull the heat from the pipes and send it via a duct system through out the building. In the summer the process is reversed. The pipes draw heat away from the house and carry it to the ground or water outside, where it is absorbed.

Global Geothermal Alliance

Launched in December 2015 at the 21st Conference of the Parties to the United Nations Framework Convention on Climate Change (COP21), the Global Geothermal Alliance offers an inclusive and neutral multi-stakeholder platform for enhanced dialogue, co-operation and co-ordinated action among public, private, intergovernmental and non-governmental actors that share a common vision of accelerating the deployment of geothermal energy for power generation and direct use. The Alliance has an aspirational goal to achieve a five-fold growth in the installed capacity for geothermal power generation and more than two-fold growth in geothermal heating by 2030*. More specifically, the Alliance aims to:

• • Foster an enabling environment to attract investments in geothermal energy.
• • Provide customised support to regions and countries with geothermal market potential.
• • Facilitate the exchange of insights and experience among key stakeholders along the geothermal value chain.
• • Identify and promote models for sharing and mitigating risks to attract private investment and integrate geothermal facilities into energy markets.
• • Promote the visibility of geothermal energy in the global energy and climate debates.

At present, the Alliance gathers over 70 Member countries and Partner institutions from geothermal industry, development partners, international finance institutions and academia.

Read Further: