What Is Geothermal Energy And What Are Three Sources Of Such Energy Apes?

What is Geothermal Energy?

Geothermal energy is thermal energy generated and stored in the Earth (1). It arises from the original formation of the planet, from radioactive decay of minerals, and from solar energy absorbed at the surface (2). This energy can emerge naturally in the form of volcanoes, hot springs, geysers, and steam vents, or can be harnessed to generate electricity and provide heating and cooling (3).

Geothermal energy is defined as heat energy from within the earth that can be extracted and used commercially. There are several different sources of geothermal energy: volcanic activity near the earth’s crust, hot springs, naturally occurring hot water reservoirs in rocks deep underground, and warm/hot rock formations that can be drilled into to inject water and create an artificial geothermal reservoir (1).

This heat energy from the earth’s interior can be used directly for heating buildings or can be converted into electricity. Geothermal power plants use steam turbines, binary cycle turbines, or other technologies to generate electricity. Geothermal heating/cooling systems use geothermal heat pumps to control temperatures inside buildings (2, 3).

(1) https://www.eia.gov/energyexplained/geothermal/

(2) https://www.energy.gov/eere/geothermal/geothermal-basics

(3) https://www.twi-global.com/technical-knowledge/faqs/geothermal-energy

Sources of Geothermal Energy

There are three main sources of geothermal energy:

Volcanoes and Hot Springs

Volcanoes and hot springs produce hydrothermal resources, which contain hot water or steam. The heat from the Earth’s interior rises toward the surface and heats underground water reservoirs. This geothermally heated water travels up to the surface through faults and fractures and manifests as hot springs or geysers.https://education.nationalgeographic.org/resource/geothermal-energy/ Areas with volcanic activity or hot springs are good locations to tap into geothermal resources and extract the heated water or steam to generate electricity.

Hot Dry Rocks

Hot dry rocks are rocks typically found 3-10 km below the Earth’s surface that are heated by the Earth’s magma but have little to no water present. To extract geothermal energy from hot dry rocks, water can be injected into the hot rocks at high pressure. The injected water is heated and returns to the surface as hot water or steam that can be used to generate electricity.https://www.energy.gov/eere/geothermal/geothermal-basics

Geo-Pressured Reservoirs

Geo-pressured reservoirs contain hot water that is under pressure from the weight and heat of overlying rocks. Drilling into these deep reservoirs releases pressurized hot water that flashes into steam when pressure is reduced. The steam can be used to drive a turbine and generate electricity just like conventional geothermal power plants.https://www.energy.gov/eere/geothermal/geothermal-basics

Volcanoes and Hot Springs

Geothermal energy from volcanoes and hot springs comes from places where magma flows close to the surface of the Earth. These areas are often located near tectonic plate boundaries where volcanic activity occurs. Hot water heated by the magma rises to the surface forming hot springs and geysers. This geothermal energy can be harnessed and used directly for heating or to generate electricity.

In volcanic regions like Iceland, hot springs are used to provide heat directly to buildings. The water is piped from the hot spring through a district heating system to provide space heating and hot water. Iceland generates over 25% of its electricity from geothermal power plants that tap into underground reservoirs of steam and hot water ¹.

California has a number of geothermal power plants located near volcanic regions that provide about 6% of the state’s electricity. The Geysers in Northern California is one of the oldest and largest geothermal power plants in the world. It generates enough electricity to power a city the size of San Francisco ¹.

Hot Dry Rocks

Hot dry rock (HDR) is a source of geothermal energy that does not have natural water present in the rock. Instead, water is injected into hot fractured basement rock at depths of 3-10 km to extract heat. The injected water circulates through the existing fractures and faults in the rock, extracting heat from the hot rocks before being pumped back up to the surface. As the heated water is pumped out, it can be used to generate electricity via a geothermal power plant at the surface. HDR has enormous potential as a vast source of geothermal energy, but is more difficult and expensive to access compared to conventional hydrothermal reservoirs. Key aspects of HDR include:

• No natural water – water must be pumped down wellbores into hot dry rocks
• Existing fractures and faults in basement rocks allow injected water to circulate and extract heat
• Water comes back up production wellbores as hot water/steam to generate electricity at surface

The HDR concept of enhancing existing rock fractures to create an artificial geothermal reservoir was first proposed in the 1970s. While technically challenging, HDR has the potential to greatly expand geothermal energy resources globally if heat extraction techniques can become more cost-competitive.

Geo-Pressured Reservoirs

Geo-pressured reservoirs refer to porous rock formations under pressure that contain hot water.[1] In these reservoirs, the water is trapped under high pressure in sedimentary rocks at depths typically between 10,000 and 30,000 feet. The high pressure forces the hot water up to the surface when extraction wells are drilled. Once at the surface, the hot pressurized water can be used to drive turbine generators and produce electricity.

Key characteristics of geo-pressured reservoirs are:

• Porous rock under high pressure contains hot brine and methane gas
• Drilling into the reservoir allows the hot pressurized fluid to rise to the surface
• The hot water energy is captured with a turbine generator

Geo-pressured reservoirs represent a potentially significant source of geothermal energy in areas like the northern Gulf of Mexico coast. However, commercial development faces challenges due to high drilling costs. Ongoing research aims to make this resource more economically viable.

[1] https://www.sciencedirect.com/topics/earth-and-planetary-sciences/geothermal-resource

Benefits of Geothermal Energy

Geothermal energy provides several key benefits that make it an attractive renewable energy source:

It is a renewable and sustainable energy source. Geothermal energy comes from natural heat within the earth, which is constantly being replenished and does not run out over time (energy.gov). Geothermal energy can be sustainably produced without depleting the earth’s resources.

Geothermal energy reduces fossil fuel use. Since it provides a constant baseload power supply, geothermal energy can replace fossil fuels like coal and natural gas for electricity generation. This reduces the amount of fossil fuels consumed and associated greenhouse gas emissions (enelgreenpower.com).

Geothermal energy has low carbon emissions. While some CO2 is emitted from geothermal power plants, the emissions are far lower per kWh compared to burning fossil fuels. Geothermal energy has among the lowest lifecycle greenhouse gas emissions of any energy source (energy.gov).

Geothermal energy is available 24/7, unlike solar or wind power. The constant heat flow from the earth allows geothermal plants to reliably generate electricity around the clock, regardless of weather or sunlight conditions (enelgreenpower.com).

Limitations of Geothermal Energy

While geothermal energy has many benefits, it also has some drawbacks that limit its uses. Some of the main limitations of geothermal energy include:

High Upfront Costs – Constructing a geothermal power plant requires significant upfront capital investment. Drilling wells thousands of feet into the earth and installing turbines and piping is an expensive endeavor. The initial cost for a geothermal power plant can be higher than for a natural gas or coal plant. This makes financing projects challenging, especially for smaller developers.

Limited to Certain Geographic Locations – Geothermal energy sources are not evenly distributed and are only located in certain parts of the world. Sources need to be relatively close to the earth’s surface with access to hot water or steam reservoirs. This geographic limitation restricts the widespread adoption of geothermal plants.

Potential Emissions if Not Managed Well – While geothermal plants emit far fewer greenhouse gases than fossil fuel plants, some geothermal reservoirs contain gases like carbon dioxide, hydrogen sulfide, ammonia, and methane that can be released if not properly managed. Proper well drilling techniques and emission control systems are important to minimize this.

While geothermal power shows great promise as a renewable energy source, these drawbacks need to be taken into consideration when examining its viability for wide-scale adoption. Careful site selection and investment in efficient designs can help maximize geothermal benefits while minimizing limitations.

Global Use of Geothermal Energy

Geothermal energy is used worldwide, but some countries utilize it more than others. According to the International Renewable Energy Agency (IRENA), the top countries using geothermal energy in terms of installed capacity as of 2021 are:

• United States – 3,813 MW
• Indonesia – 2,042 MW
• Philippines – 1,928 MW
• Türkiye – 1,620 MW
• New Zealand – 1,139 MW

The U.S. Energy Information Administration reports that in 2021, global geothermal electricity generation was around 95 billion kWh, with the United States generating about 17 billion kWh. Significant growth potential remains, as geothermal accounted for only 0.5% of total global renewable energy generation. The worldwide theoretical potential for geothermal resources is estimated to be over 200 GW, but only about 15 GW of capacity is currently installed. With supportive policies and technological advances, geothermal capacity is projected to reach 21-26 GW by 2030.

Sources:

• https://www.irena.org/publications/2023/Feb/Global-geothermal-market-and-technology-assessment
• https://www.eia.gov/energyexplained/geothermal/use-of-geothermal-energy.php

Recent Developments

Geothermal power generation is seeing renewed interest and growth due to new technologies that allow access to geothermal resources that were previously unreachable or uneconomical. One key development is enhanced geothermal systems (EGS), which inject water into hot dry rocks deep underground at high pressures to create cracks and circulation paths that enable heat extraction (1). EGS has the potential to vastly expand geothermal energy production.

Other innovations like compact wellhead power plants allow small-scale distributed geothermal generation near the energy source. Advanced drilling techniques such as high-temperature turbines and diamond drill bits enable deeper drilling into hotter resources (2). Integration with other technologies like solar thermal is also being explored (3).

Many governments are implementing policies and incentives to accelerate geothermal development. In the U.S., tax incentives have been extended to 2034 for geothermal projects that start construction by the end of 2032 (1). Government research is also driving innovations in EGS through programs like the U.S. Department of Energy’s FORGE initiative (4). Countries like Indonesia, Kenya, Turkey and New Zealand have significant expansion targets, with government commitment to enable growth through mapping of resources, streamlined permitting, and financial incentives (5).

Sources:

(1) https://www.energy.gov/eere/geothermal/listings/geothermal-energy-news

(2) https://www.thinkgeoenergy.com/

(3) https://www.nytimes.com/topic/subject/geothermal-power

(4) https://www.energy.gov/eere/forge

(5) https://iea-gia.org/geothermal-energy/

Future Outlook

The future looks bright for geothermal energy. According to projections, geothermal electricity generation capacity is expected to grow by over 26% globally between 2020 and 2025 (https://www.cralloys.com/portfolio/the-future-of-geothermal-energy/). Areas with untapped potential like East Africa, Southeast Asia, and South America are likely to see the most growth as developers explore new sites for geothermal plants.

Geothermal is poised to play an increasingly important role in the global renewable energy mix. The geothermal industry expects installed global geothermal power capacity to nearly double from around 14,000 MW today to over 27,000 MW by 2027, despite geothermal energy currently only accounting for about 0.3 percent of total U.S. utility-scale electricity generation. Geothermal’s baseload capacity and ability to provide power 24/7 make it a critical clean energy source to balance the intermittency challenges of wind and solar power (https://e360.yale.edu/features/can-geothermal-power-play-a-key-role-in-the-energy-transition).

With improved technologies like enhanced geothermal systems (EGS), geothermal has the potential to unlock energy reserves previously thought to be unviable. Advancements in drilling techniques, fracturing, and reservoir engineering can open up new sources of heat like dry and low permeability rocks. The steady, renewable heat emitted from the earth’s crust will continue propelling geothermal forward as a sustainable energy solution.