What Is The Energy From The Hot Interior Of The Earth?

What is Geothermal Energy?

Geothermal energy is thermal energy generated and stored in the Earth (1). It arises from the hot interior of the planet, with temperatures as high as 7200°F, only a few miles below the surface. The energy originates from the original formation of the planet, radioactive decay of minerals, and from solar energy absorbed at the surface. Geothermal energy is a renewable energy source because heat is continuously produced inside the Earth (2).

Geothermal energy utilizes the heat from the Earth’s interior to provide energy in the form of electricity and direct heating and cooling. It is considered a clean, renewable source of energy. Geothermal power plants tap into underground reservoirs of steam and hot water to spin turbines that generate electricity (3). Direct uses take advantage of geothermal heat by directly transferring it for purposes like heating buildings, growing plants in greenhouses, drying crops, heating water at fish farms, and several industrial processes.

(1) https://www.energy.gov/eere/geothermal/geothermal-basics
(2) https://www.eia.gov/energyexplained/geothermal/
(3) https://www.twi-global.com/technical-knowledge/faqs/geothermal-energy

How is Geothermal Energy Created?

Geothermal energy is produced by the radioactive decay of minerals like uranium, thorium, and potassium found deep within the Earth’s core. These radioactive elements produce heat as they break down into stable elements over billions of years. The heat generated from the breakdown of radioactive minerals transfer outwards towards the Earth’s crust.

Molten rock, known as magma, carries heat from the Earth’s interior outward. The magma convects and conducts heat from deep within the mantle and crust through fractures and pore spaces in rocks. This heat transfer process creates hot subsurface zones that make geothermal energy production possible. According to the National Renewable Energy Laboratory, these zones “can reach temperatures between 250 and 700°F at depths of 10,000 feet or more below the Earth’s surface.”

Types of Geothermal Energy Systems

There are two main types of geothermal energy systems that are used to harness the Earth’s internal heat – geothermal power plants and geothermal heating/cooling systems.

Geothermal power plants utilize the heat from the Earth’s interior to produce electricity. As explained by the U.S. Department of Energy, there are three main types of geothermal power plant technologies:1

• Dry steam power plants that use steam from a geothermal reservoir to directly turn turbine generators.
• Flash steam power plants that pull deep, high-pressure hot water into lower pressure tanks and use the resulting flashed steam to drive turbine generators.
• Binary cycle power plants that pass hydrothermal fluids through a heat exchanger to heat a separate fluid that vaporizes and drives turbine generators.

According to the California Energy Commission, all geothermal power plants utilize steam to spin large turbines connected to electrical generators, but the geothermal fluid source and conversion process differ.2

Geothermal heating/cooling systems, also referred to as geothermal heat pumps, utilize shallow ground or water temperatures to heat and cool buildings. These systems transfer heat between the Earth and buildings using a network of pipes called a loop system. In the winter, the systems draw heat from the Earth into the building and in the summer, they transfer heat from the building back into the cooler Earth.

Locations of Geothermal Resources

Geothermal energy sources are found all across the globe, but they are concentrated in regions with active tectonic plate boundaries and volcanic activity. According to the U.S. Energy Information Administration, the United States leads the world in geothermal electricity generation with over 3,500 MW of installed capacity, primarily located in the western states like California, Nevada, Utah, and Hawaii where hot springs and geysers are common EIA source. Other top countries utilizing geothermal power include Indonesia, the Philippines, Turkey, New Zealand, Iceland, Italy and Mexico.

Some of the highest temperature geothermal resources in the world are found along the Pacific Rim in places like Japan, Indonesia, the Philippines, New Zealand and the western coasts of North and South America. Giant calderas in western North America at Yellowstone, Long Valley and Valles Caldera also host potential geothermal resources. Iceland stands out for successfully generating over 25% of its electricity from geothermal sources due to its location atop the divergent boundary of the North American and Eurasian tectonic plates Enbridge source.

Benefits of Geothermal Energy

Geothermal energy offers several key benefits that make it an attractive renewable energy source. First, geothermal is a renewable energy source. The heat from the Earth’s interior is constantly being replenished and will be available for as long as the Earth exists (Enel Green Power).

Second, using geothermal energy reduces our dependence on fossil fuels like coal, oil, and natural gas. The thermal energy harnessed from the Earth’s crust can be used to produce electricity, heat homes and buildings, or power industrial processes – all applications that currently rely heavily on fossil fuels. Switching to geothermal energy decreases fossil fuel consumption and associated greenhouse gas emissions (Department of Energy).

Third, geothermal energy has much lower emissions compared to conventional power plants. Geothermal plants emit on average 1/3rd the carbon dioxide of a natural gas plant per megawatt-hour generated. The emissions are low since no fuels are combusted for energy generation (Department of Energy).

Limitations of Geothermal

While geothermal energy has several advantages, it also comes with some limitations that restrict its widespread adoption. Some of the main limitations of geothermal energy include:

High upfront costs – Constructing a geothermal power plant requires substantial initial investments, which can range from $2-5 million per installed megawatt capacity. Drilling exploratory wells and building the power plant infrastructure drives up the costs.^[1] The high initial capital makes geothermal unsuitable for distributed power generation.

Limited to certain locations – Geothermal energy can only be harnessed in areas with optimal hydrothermal resources, like volcanic regions or hot spots. This geographical restriction limits the widespread adoption of geothermal across the world. Currently, only about 8-10 countries actively use geothermal for power generation.^[2]

Potential emissions – While geothermal plants emit far fewer greenhouse gases than fossil fuel plants, geothermal reservoirs can release trace amounts of toxic gases like hydrogen sulfide, ammonia, methane, and carbon dioxide. Proper mitigation systems need to be in place.^[3]

Despite these limitations, advances in technology and drilling techniques are helping make geothermal more viable and cost-effective over time.

<sup>[1] https://www.greenmatch.co.uk/blog/2014/04/advantages-and-disadvantages-of-geothermal-energy
[2] https://www.twi-global.com/technical-knowledge/faqs/geothermal-energy/pros-and-cons

[3] https://www.solarreviews.com/blog/geothermal-energy-pros-and-cons</sup>

Geothermal Power Generation

There are three main types of geothermal power plants that are used to generate electricity:

• Flash plants – These plants pull hot, high-pressure water from geothermal reservoirs. The steam then rotates turbines to generate electricity. Flash plants are the most common type of geothermal power plant.
• Dry steam plants – These plants use steam from geothermal reservoirs to directly rotate turbines. The first geothermal power plant was a dry steam plant built in Italy in 1904.
• Binary cycle power plants – These plants pass geothermal fluid through heat exchangers to heat a secondary fluid with a much lower boiling point than water. This causes the secondary fluid to flash to vapor and rotate the turbine.

In 2019, the global geothermal electricity generation capacity was around 14.8 GW, with the largest capacities located in the United States (3.7 GW), Indonesia (2.1 GW), and the Philippines (1.9 GW) [1]. Geothermal energy provides about 6-7% of the total electricity generation in the United States, while providing about 27% in the Philippines and 26% in Kenya [2].

Direct Uses of Geothermal

Geothermal energy has many direct uses that provide heating and cooling for homes, businesses, agriculture, and more. Direct use takes advantage of geothermal reservoirs that exist at relatively shallow depths and low-to-moderate temperatures.

One of the most common direct uses is for space heating and cooling. Geothermal heat pumps can tap into shallow ground or water temperatures to heat and cool buildings at much higher efficiencies than conventional systems. According to the Geothermal Technologies Program, over 1 million homes and buildings in the U.S. use geothermal heat pumps today.

Geothermal resources are also used extensively for heating greenhouses, aquaculture, and a variety of agricultural drying processes. The warm water can nurture plants and fish in colder climates and the heat can also be used to dry fruits, vegetables, and herbs. Countries like Iceland and New Zealand have utilized geothermal heating in greenhouses and for drying wool and coconut products.

Geothermal waters have been used for bathing and therapeutic purposes throughout human history. Hot springs have served as public baths in Europe, Japan, and the Americas for centuries. Today, many hot spring resorts and spas use the mineral-rich waters for relaxation and treatment.

Future of Geothermal

Enhanced geothermal systems (EGS) represent an exciting frontier for geothermal energy. EGS technologies allow us to access geothermal resources almost anywhere by drilling into hot, dry rock and pumping water through it to create a geothermal reservoir and produce electricity. According to the U.S. Department of Energy, EGS could provide 100 gigawatts of economically viable electricity generation capacity in the United States by 2050, representing a tenfold increase. EGS offers the potential to dramatically expand geothermal energy usage and enable geothermal power generation in many new locations worldwide.

Overall, geothermal energy has significant room for growth globally. The International Energy Agency projects the installed capacity for geothermal electricity generation could grow from around 14 gigawatts today to almost 60 gigawatts by 2040. With supportive policies and declining costs, growth could be even faster. Geothermal heat pumps for heating and cooling buildings also hold major potential. The U.S. National Renewable Energy Laboratory notes geothermal energy has the technical potential to meet U.S. building energy needs more than 50 times over.

Key Facts About Geothermal

Geothermal energy accounted for 0.4% of total U.S. electricity generation in 2022, producing an estimated 17 billion kilowatthours according to the U.S. Energy Information Administration (EIA). The United States had geothermal power plants in seven states as of 2022.

Geothermal electricity generation capacity was about 3.8 gigawatts in 2021, an increase of about 17% from 2020 according to the Geothermal Resources Council (GRC).

The Western Governors’ Association projects U.S. geothermal power capacity could increase up to 60 gigawatts by 2050, a more than 15-fold increase (WGA). Significant untapped potential remains.

Geothermal power production emits an average of 20 grams of CO2-equivalent per kilowatthour, making it one of the lowest-carbon energy sources available according to Department of Energy analysis (DOE). This can help reduce greenhouse gas emissions from electricity generation.