Geothermal, The Power Of Earth

Geothermal Energy

Earth's internal heat is thermal energy generated from radioactive decay and continual heat loss from Earth's formation. Temperatures at the core–mantle boundary may reach over 4000 °C (7200 °F). The high temperature and pressure in Earth's interior cause some rock to melt and solid mantle to behave plastically, resulting in portions of the mantle convicting upward since it is lighter than the surrounding rock. Rock and water is heated in the crust, sometimes up to 370 °C (700 °F).

With water from hot springs, geothermal energy has been used for bathing since Paleolithic times and for space heating since ancient Roman times, but it is now better known for electricity generation. Worldwide, 11,700 megawatts (MW) of geothermal power was available in 2013. An additional 28 gigawatts of direct geothermal heating capacity is installed for district heating, space heating, spas, industrial processes, desalination and agricultural applications as of 2010.

Geothermal power is cost-effective, reliable, sustainable, and environmentally friendly, but has historically been limited to areas near tectonic plate boundaries. Recent technological advances have dramatically expanded the range and size of viable resources, especially for applications such as home heating, opening a potential for widespread exploitation. Geothermal wells release greenhouse gases trapped deep within the Earth, but these emissions are much lower per energy unit than those of fossil fuel.

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. The main advantages are that it is not depending on weather conditions and has very high capacity factors; for these reasons, geothermal power plants are capable of supplying base-load electricity, as well as providing ancillary services for short and long-term flexibility in some cases.

There are different geothermal technologies with distinct levels of maturity. Technologies for direct uses like district heating, geothermal heat pumps, greenhouses, and for other applications are widely used and can be considered mature. The technology for electricity generation from hydrothermal reservoirs with naturally high permeability is also mature and reliable, and has been operating since 1913. Many of the power plants in operation today are dry steam plants or flash plants (single, double and triple) harnessing temperatures of more than 180°C. However, medium temperature fields are more and more used for electricity generation or for combined heat and power thanks to the development of binary cycle technology, in which geothermal fluid is used via heat exchangers to heat a process fluid in a closed loop. Additionally, new technologies are being developed like Enhanced Geothermal Systems (EGS), which are in the demonstration stage.

To promote wider geothermal energy development, IRENA coordinates and facilitates the work of the Global Geothermal Alliance (GGA) – a platform for enhanced dialogue and knowledge sharing for coordinated action to increase the share of installed geothermal electricity and heat generation worldwide.

The International Geothermal Association (IGA) has reported that 10,715 megawatts (MW) of geothermal power in 24 countries is online, which was expected to generate 67,246 GWh of electricity in 2010. This represents a 20% increase in online capacity since 2005. IGA projects growth to 18,500 MW by 2015, due to the projects presently under consideration, often in areas previously assumed to have little exploitable resources.

In 2010, the United States led the world in geothermal electricity production with 3,086 MW of installed capacity from 77 power plants. The largest group of geothermal power plants in the world is located at The Geysers, a geothermal field in California. The Philippines is the second highest producer, with 1,904 MW of capacity online. Geothermal power makes up approximately 27% of Philippine electricity generation.

In 2016, Indonesia set in third with 1,647 MW online behind USA at 3,450 MW and the Philippines at 1,870 MW, but Indonesia became second due to an additional online 130 MW at the end of 2016 and 255 MW in 2017. Indonesia's 28,994 MW are the largest geothermal reserves in the world, and it is predicted to overtake the US in the next decade.

In India

In India, by the time, geothermal energy installed capacity is experimental; however, the potential capacity is more than 10,000 MW.

Indian Scenario

India has reasonably good potential for geothermal; the potential geothermal provinces can produce 10,600 MW of power.

Though India has been one of the earliest countries to begin geothermal projects way back in the 1970s, but at present there are no operational geothermal plants in India. There is also no installed geothermal electricity generating capacity as of now and only direct uses (eg.Drying) have been detailed.

Thermax, a capital goods manufacturer based in Pune, has entered an agreement with Icelandic firm Reykjavík Geothermal. Thermax is planning to set up a 3 MW pilot project in Puga Valley, Ladakh (Jammu & Kashmir). Reykjavík Geothermal will assist Thermax in exploration and drilling of the site.

India’s Gujarat state is drafting a policy to promote geothermal energy

Following are the six most promising geothermal energy sites in India −

Tattapani in Chhattisgarh

Puga in Jammu & Kashmir

Cambay Graben in Gujarat

Manikaran in Himachal Pradesh

Surajkund in Jharkhand

Chhumathang in Jammu & Kashmir

Following are the six major geothermal provinces in India

Himalayan Province e.g. Himachal Pradesh, Jammu & Kashmir, etc.

Areas of Faulted blocks e.g. Aravalli belt, Naga-Lushi, West coast regions and Son-Narmada lineament.

Volcanic Arc e.g. Andaman and Nicobar Arc (Barren Island).

Deep sedimentary basin of Tertiary age e.g. Cambay basin in Gujarat.

Radioactive Province e.g. Surajkund, Hazaribagh, and Jharkhand.

Cratonic Province e.g. Peninsular India.

Advantages of Geothermal Energy

The first advantage of using geothermal heat to power a power station is that, unlike most power stations, a geothermal system does not create any pollution. It may once in a while release some gases from deep down inside the earth, that may be slightly harmful, but these can be contained quite easily. Geothermal power plants have sulphur-emissions rates that average only a few percent of those from fossil -fuel alternatives. The newest generation of geothermal power plants emits only ~135 gm of carbon (as carbon dioxide) per megawatt-hour (MW-hr) of electricity generated. This figure compares with 128 kg /MW-hr of carbon for a plant operating on natural gas (methane) and 225 kg/MW-hr of carbon for a plant using bituminous coal. Nitrogen oxide emissions are much lower in geothermal power plants than in fossil power plants. Nitrogen-oxides combine with hydrocarbon vapours in the atmosphere to produce ground-level ozone, a gas that causes adverse health effects and crop losses as well as smog.

The cost of the land to build a geothermal power plant on, is usually less expensive than if you were planning to construct an; oil, gas, coal, or nuclear power plant. The main reason for this is land space, as geothermal plants take up very little room, so you don’ t need to purchase a larger area of land.

Another factor that comes into this is that because geothermal energy is very clean, you may receive tax cuts, and/or no environmental bills or quotas to comply with the countries carbon emission scheme (if they have one).

No fuel is used to generate the power, which in return, means the running costs for the plants are very low as there are no costs for purchasing, transporting, or cleaning up of fuels you may consider purchasing to generate the power.

The overall financial aspect of these plants is outstanding, you only need to provide power to the water pumps, which can be generated by the power plant itself anyway. Because they are modular, then can be transported conveniently to any site. Both baseline and peaking power can be generated.

Construction time can be as little as 6 months for plants in the range 0.5 to 10 MW and as little as 2 years for clusters of plants totaling 250 MW or more.

Disadvantages of Geothermal Energy

Fluids drawn from the deep earth carry a mixture of gases, notably carbon dioxide (CO2), hydrogen sulfide (H2S), methane (CH4) and ammonia (NH3). These pollutants contribute to global warming, acid rain, and noxious smells if released. Existing geothermal electric plants emit an average of 122 kilograms (269 lb) of CO2 per megawatt-hour (MW·h) of electricity, a small fraction of the emission intensity of conventional fossil fuel plants. Plants that experience high levels of acids and volatile chemicals are usually equipped with emission-control systems to reduce the exhaust.

In addition to dissolved gases, hot water from geothermal sources may hold in solution trace amounts of toxic chemicals such as mercury, arsenic, boron, and antimony. These chemicals precipitate as the water cools, and can cause environmental damage if released. The modern practice of injecting cooled geothermal fluids back into the Earth to stimulate production has the side benefit of reducing this environmental risk.

Plant construction can adversely affect land stability. Subsidence has occurred in the Wairakei field in New Zealand and in Staufen im Breisgau, Germany. Enhanced geothermal systems can trigger earthquakes as part of hydraulic fracturing. The project in Basel, Switzerland was suspended because more than 10,000 seismic events measuring up to 3.4 on the Richter Scale occurred over the first 6 days of water injection.

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