Geothermal Energy Explained: All You Need to Know

Geothermal Energy Explained: All You Need to Know

By
Grace Smoot

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Geothermal energy extracts heat from the Earth’s core to generate energy that produces little to no waste products or carbon dioxide (CO2) emissions. So, we had to ask: What is geothermal energy really, and how can it help mitigate climate change?

Geothermal energy is the conversion of heat from the Earth’s core into electrical energy. Per KWh produced, geothermal emits 38 grams of CO2 on a life-cycle basis, the 6th lowest out of all fuel types. Geothermal energy helps combat climate change and has various environmental benefits.

Keep reading to find out all about what geothermal energy is, its global capacity, its carbon footprint, its environmental benefits and drawbacks, and how it can mitigate climate change.

The Big Picture of Geothermal Energy

Geothermal energy contributes to the avoidance of greenhouse gas (GHG) emissions from the burning of fossil fuels (e.g., coal, oil, natural gas). It is classified as a renewable energy source because the Earth has an almost unlimited supply of heat generated by its core.

How Is Geothermal Energy Defined

Geothermal energy is produced when radioactive materials in the rock and fluid of the earth’s core decay. Drilling down to hot water reservoirs up to a mile below the surface creates steam that rotates a turbine, which spins a generator to generate electricity. 

Geothermal: involving or produced by the heat that is inside the earth”

Cambridge Dictionary

Geothermal is mostly found along major tectonic plate boundaries where volcanoes are located. Because the Earth has an almost unlimited supply of heat generated by its core, and the water extracted from the reservoirs can be recycled via re-injection into the ground, geothermal energy is a renewable energy source. 

What Are the Different Types of Geothermal Energy 

The three main types of geothermal power plants are: 

  1. Dry Steam: Wells are drilled into underground reservoirs of steam. The steam is piped directly from the well to the power plant where it powers turbines and generators.
  1. Flash Steam: The most common type of geothermal power plant. Very hot (360 degrees Fahrenheit, 182 degrees Celsius) water flows up through wells towards the surface under its own pressure. As it reaches the surface, some of the water boils into steam. The steam is then separated from the water and is then used to power turbines and generators at the power plant.
  1. Binary Cycle: Wells are drilled into underground reservoirs of hot water (225-360 degrees Fahrenheit, 107-182 degrees Celsius). The heat from the water is used to boil a working fluid, an organic compound with a low boiling point. This working fluid is vaporized into steam which is then used to power turbines and generators at the power plant. The water is then injected back into the ground where it is reheated and can be used again. There are virtually no air emissions during this process because the working fluid and water are kept separate during the process.
What geothermal energy isGeothermal energy is produced when radioactive materials in the rock and fluid of the earth’s core decay. 
What the different types of geothermal energy are The three main types of geothermal power plants are dry steam, flash steam, and binary cycle. 
How geothermal energy worksHarnessing geothermal energy involves drilling down to reservoirs and extracting the hot water to produce steam, which turns turbines and powers generators to create electricity.
The global capacity of geothermal energyCurrently, geothermal energy represents 0.5% of the global renewable electricity market. We produced 95,251 gigawatts (GWh) of energy from 14,696 megawatts (MW) of installed geothermal capacity in 2021. The US, Indonesia, the Philippines, and Turkey are the top geothermal energy-producing countries.
The carbon footprint of geothermal energyOn a life-cycle basis, geothermal energy emits 38 grams of CO2 equivalent per kWh of electricity produced, the 6th lowest out of all fuel types. 
The environmental benefits of geothermal energyGeothermal energy protects air quality, has a minimal land use impact, generates very few waste products, mitigates climate change, promotes energy independence, and creates jobs.
The environmental drawbacks of geothermal energyGeothermal energy can be location-specific (e.g., tectonic plate boundaries) and can trigger earthquakes via the injection of high-pressure fluids close to fault lines.
Geothermal energy and climate changeGeothermal energy combats climate change by mitigating the temperature rise, sea-level rise, ice melting, and ocean acidification associated with global warming.

How Does Geothermal Energy Work

To harness geothermal energy, geothermal power plants convert heat from the Earth’s core into electrical energy which then turns turbines and spins a generator to create electricity. 

How Does Geothermal Energy Actually Produce Energy

All three types of geothermal power plants (e.g., dry steam, flash steam, binary cycle) harvest water from the earth’s core in the same manner, by drilling down to reservoirs and extracting the hot water to produce steam, turn turbines, and power generators to create electricity.

The electricity is either stored for later use or is transported to a substation where it is transmitted to consumers by transmission lines. Transformers receive the electricity and either increase or decrease the voltage as needed before it can be delivered to consumers. 

What Is the Global Capacity of Geothermal Energy

Experts estimate that we could supply humanity’s total energy needs for the next 2 million years with only 0.1% of the heat content of the Earth. Yet to date, geothermal remains a relatively untapped resource. 

Installed geothermal capacity reached a record high of 14,877 megawatts (MW) in 2022

Illustration of Installed geothermal energy capacity from Our World in Data
Our World in Data: Installed geothermal energy capacity

The US has 2,643 MW of installed geothermal energy capacity, the most in the world. They are closely followed by Indonesia, the Philippines, Turkey, New Zealand, and Mexico. 

Illustration of Installed geothermal energy capacity, 2022 from Our World in Data
Our World in Data: Installed geothermal energy capacity, 2022

Turkey has experienced a 9,296% increase in installed geothermal capacity, from 18 MW in 2000 to 1,691 MW in 2022. In the past decade, they have drilled over 10,000 geothermal wells and increased their number of geothermal power plants from 3 to 49.

Kenya has experienced a 1,536% increase in installed geothermal capacity, from 58 MW in 2000 to 949 MW in 2022. Easy access to geothermal sources has led to Kenya becoming an expert in the geothermal field and encouraging neighbors Ethiopia and Djibouti to begin developing their geothermal sources.

Global electricity generation from geothermal energy reached an all-time high of 95,000 gigawatt-hours in 2021. However, geothermal still represents only 0.5% of the global renewable electricity market as of 2022. 

Illustration of Geothermal Electricity Generation from International Renewable Energy Agency
International Renewable Energy Agency: Geothermal Electricity Generation

The US is the world leader in geothermal electricity generation. 7 US states (out of 50) were responsible for generating roughly 17 billion kilowatt hours (kWh) of electricity, or 0.4% of total US utility-scale electricity generation, in 2022. The state of California generated almost 70% of US geothermal electricity followed by 24% from the state of Nevada.

The future of geothermal energy will be heavily influenced by ambitious government targets, policy support, increasing competitiveness of geothermal energy companies, and decreasing the upfront costs associated with installing geothermal technologies.

What Is the Carbon Footprint of Geothermal Energy

The carbon footprint is one of the ways we measure the effects of human-induced global climate change. It primarily focuses on the greenhouse gas (GHG) emissions associated with consumption and includes other emissions such as methane (CH4), nitrous oxide, and chlorofluorocarbons (CFCs).

Carbon footprint: the amount of greenhouse gasses and specifically carbon dioxide emitted by something (such as a person’s activities or a product’s manufacture and transport) during a given period

Merriam Webster

Basically, it is the amount of carbon emitted by an activity or an organization. This includes GHG emissions from fuel that we burn directly (e.g., heating a home or driving a car) and GHG emissions from manufacturing the products that we use (e.g., power plants, factories, and landfills). 

On a life-cycle basis, geothermal energy emits 38 grams of CO2 equivalent per kWh of electricity produced, the 6th lowest out of all fuel types. 

Have a look at the illustration below to see the average life-cycle CO2 equivalent emissions of different energy sources and how they compare to geothermal energy.

Illustration of the Average life-cycle CO2 equivalent emissions from World Nuclear Association
World Nuclear Association: Average life-cycle CO2 equivalent emissions

When discussing the carbon footprint of geothermal energy, we must take into account carbon emissions across the energy’s building, operating, and building back phases.

The life-cycle stages of geothermal energyEach stage’s carbon footprint
Building of geothermal energyCO2 emissions from drilling geothermal wells and construction of geothermal power plants
Operating of geothermal energyCO2 emissions from the operation of geothermal power plants
Building back of geothermal energyLittle to no CO2 emissions or waste products

Throughout its life cycle, geothermal energy produces roughly 5% of the CO2 emissions per unit of electricity that coal produces. In the US alone, annual geothermal energy resources effectively offset the emission of 4.1 million metric tons of CO2 when compared to conventional coal-fired plants.

Geothermal heat pumps can last more than 20 years, and the underground infrastructure has a historical life expectancy of up to 50 years. This makes them a long-term, reliable source of energy. 

Because geothermal energy has a large electricity generation potential – and production has steadily increased in the last decade – it is important to understand what its carbon footprint is. And how its carbon emissions affect the global climate change process.

Related: Are you interested in learning more about the carbon footprint of geothermal energy? Check it out in this article here: “What Is the Carbon Footprint of Geothermal Energy? A Life-Cycle Assessment

How Environmentally Friendly Is Geothermal Energy

The environmental impacts of geothermal energy depend on how the energy is used and how it is converted to useful energy. 

Environmentally friendly: (of products) not harming the environment.”

Cambridge Dictionary

Overall, geothermal energy is environmentally friendly because it is a renewable energy source that releases minute amounts of CO2.

What Are The Environmental Benefits of Geothermal Energy

Here are the ways in which geothermal energy benefits the environment:

  • Few waste products: Most geothermal plants do not create measurable solid waste byproducts. 
  • Climate change mitigation: Geothermal energy has an average life-cycle CO2 equivalent emission value that is much less than coal, 38g of CO2 equivalent per kWh compared to 820g of CO2 equivalent per kWh, respectively. This reduction in CO2 emissions, in turn, reduces the effects of global climate change including increasing temperatures, rising sea levels, melting of sea ice, changing precipitation patterns, and ocean acidification.
  • Energy Independence: Being able to produce our own electricity in the U.S. without the aid of foreign countries is an important step to help us become more self-sufficient. Former President George W. Bush signed the Energy Independence and Security Act of 2007 to reduce U.S. dependence on oil, expand the production of renewable fuels (and confront global climate change). 

What Are The Environmental Drawbacks of Geothermal Energy

Because geothermal energy is a relatively clean energy source, there are few environmental drawbacks. These can include: 

  • Location specificity: Geothermal reservoirs occur deep underground and are not detectable from the surface. Areas where geothermal does come to the surface include volcanoes, fumaroles, hot springs, and geysers. These are only found near tectonic plate boundaries. The largest area of harvestable geothermal energy can be found at the Ring of Fire, which lines the edges of the Pacific Ocean. 

Negative environmental impacts can be minimized by directional drilling, siting power plants away from major fault lines, properly disposing of hazardous waste captured by the scrubbers, and recycling the geothermal steam and water via re-injection into the ground.

Why Is Geothermal Energy Important to Fight Climate Change

Climate change is arguably the most severe, long-term, global impact of fossil fuel combustion. Every year, approximately 33 billion tons (bt) of CO2 are emitted from burning fossil fuels. The carbon found in fossil fuels reacts with oxygen in the air to produce CO2. This warms the earth by acting as a heating blanket, and a warmer earth comes with a host of negative side effects. 

Using geothermal energy instead of fossil fuel energy helps mitigate the following negative effects of climate change:

The more we reduce CO2 emissions, the more we slow the rate of temperature rise, sea-level rise, ice melting, and ocean acidification. When these rates are slowed, the earth’s biodiversity does not have to struggle to adapt to temperature and pH changes. People will not be displaced due to the flooding of coastal areas. And icebergs will continue to provide climate regulation. 

To help keep global temperature rise below 1.5C, as outlined in the Paris Agreement, we must shift at least 80% of our electricity generation to low-carbon sources. Over 140 countries have stated a net-zero target, covering roughly 88% of the world’s emissions. However, under current conditions, global emissions are projected to increase by 9% by 2030 instead of the 45% reduction in emissions that is needed.

Final Thoughts

Geothermal energy takes advantage of the heat from the Earth’s core and converts it into energy which is then used to turn turbines and spin a generator to produce electricity. The 3 main types of geothermal plants are dry steam, flash steam, and binary cycle, the last of which is the most commonly used today. 

Geothermal energy is an environmentally friendly energy source with a low carbon footprint across its building, operating, and building back phases. It mitigates climate change, improves air quality, creates jobs, and promotes energy independence. Any negative environmental impacts can be minimized by directional drilling, siting power plants away from major fault lines, and recycling the geothermal steam and water via re-injection into the ground.

Despite various benefits, geothermal energy remains an untapped resource, only representing 0.5% of the global renewable electricity market. As we look towards a future powered by renewables, geothermal energy is a sustainable energy source that benefits both our atmosphere and Earth’s biota.

Stay impactful,

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