How Does Geothermal Power Work And How Does It Help The Environment?

Table of Contents

What is Geothermal Energy?

Geothermal energy is heat energy generated and stored in the Earth (EIA, 2023). It is a renewable energy source because the heat is continuously produced inside the Earth from the slow decay of radioactive particles in the core, mantle, and crust (TWI Global, 2023). Geothermal comes from the Greek words geo (earth) and therme (heat).

Geothermal energy relies on the high temperatures beneath the Earth’s surface, which range from 4000-12000 degrees Fahrenheit just 10-20 miles down (Energy.gov, 2023). This heat can be accessed by drilling water or steam wells in areas with geothermal reservoirs. The geothermal energy can then be used directly to provide heat or to generate clean electricity.

Because geothermal energy is constantly replenished, it is considered a renewable energy source. Once in place, geothermal power plants can operate cleanly and reliably for decades.

Types of Geothermal Power Plants

There are three main types of geothermal power plants:

Dry Steam Power Plants

Dry steam power plants use steam directly from a geothermal reservoir to turn turbines and generate electricity. The first geothermal power plant was a dry steam plant built in Italy in 1904. Dry steam reservoirs are relatively rare and account for only about 10-15% of geothermal energy production today. According to the California Energy Commission, the largest dry steam field in the world is The Geysers complex in California, which generates over 725 megawatts of power ¹.

Flash Steam Power Plants

Flash steam power plants use water at temperatures over 360°F (182°C) that is sprayed into a tank held at a much lower pressure, causing the water to rapidly vaporize into steam. The steam is then used to power turbines. Flash plants are the most common type of geothermal plant today, accounting for about 65% of geothermal power generation worldwide.

Binary Cycle Power Plants

Binary cycle power plants use moderate-temperature water from geothermal reservoirs (roughly 225-360°F or 107-182°C) to heat a secondary fluid with a much lower boiling point that vaporizes and drives turbines. The water is not directly flashed into steam. The water and secondary fluid are kept separated during the whole process, so the water can be reinjected back into the reservoir to be reused. Binary cycle plants represent about 25% of geothermal capacity worldwide.

How Geothermal Power is Generated

Geothermal power plants convert thermal energy from the Earth into electricity. This is done by extracting hot water or steam from geothermal reservoirs located below the Earth’s surface and using it to drive turbine generators which produce electricity (1).

There are three main types of geothermal power plants:

Dry steam plants use steam from a geothermal reservoir to directly drive turbine generators.
Flash steam plants take high-pressure hot water from deep inside the earth and convert it to steam to drive the turbines.

Binary cycle plants transfer the internal heat from geothermal water to another liquid which boils at a lower temperature than water. This causes the second liquid to vaporize, which then drives the turbines (2).

In all three types of plants, the spinning turbine converts the geothermal steam or vapor into mechanical energy. The turbine then spins a shaft connected to a generator which produces electricity. After driving the turbine, the steam is cooled, condensed back into water, and is either disposed of or re-injected back into the geothermal reservoir to be reused (1).

The process extracts clean, renewable energy from hot water sources deep beneath the earth’s surface in a sustainable way. Geothermal reservoirs are naturally replenished by heat from the earth’s core so they provide a consistent and reliable source of energy.

Sources:

(1) https://www.energy.gov/eere/geothermal/electricity-generation

(2) https://www.nrel.gov/research/re-geo-elec-production.html

Environmental Benefits

One of the biggest environmental benefits of geothermal energy is that it emits little to no greenhouse gases. Unlike fossil fuel power plants, geothermal power plants do not burn fuel to generate electricity, so they release minimal emissions. According to the U.S. Department of Energy, geothermal power plants emit on average less than 5% of the carbon dioxide emissions of a fossil fuel plant. The emissions from geothermal mainly come from the infrastructure and construction phase, as well as traces released from the reservoir.

Geothermal systems are also considered renewable energy since the heat emanating from the Earth’s interior is constantly being replenished. The reinjection of geothermal fluids back into the reservoir allows the resource to be harvested in a sustainable way. Geothermal power does not produce problematic waste like nuclear energy or combustion byproducts like fossil fuels.

In addition, geothermal power has a small land footprint compared to other energy sources. The actual power plant itself takes up a modest amount of space, and geothermal can often be built on land not useful for other purposes. This avoids having to clear new land and preserves natural habitats.

Geographic Locations for Geothermal

Geothermal power plants are located in areas with adequate underground reservoirs of hot water or steam. These geothermal reservoirs are typically found along major tectonic plate boundaries where volcanic activity and earthquakes often occur. The western United States, Alaska, Hawaii, and Iceland are prime locations for geothermal energy due to their proximity to tectonic plate boundaries.

According to the U.S. Energy Information Administration, most of the geothermal power plants in the United States are located in western states and Hawaii where geothermal resources are closer to the surface of the Earth [1]. California generates the most geothermal electricity in the country, with power plants at The Geysers in the northern part of the state. Nevada, Utah, Hawaii, Idaho, and Oregon also have substantial geothermal power generation.

Outside of the U.S., countries like Iceland, New Zealand, Indonesia, and Turkey have ideal locations along tectonic plate boundaries to take advantage of geothermal energy. Iceland in particular generates over 25% of its electricity from geothermal sources because it is located directly on the Mid-Atlantic Ridge.

Capacity and Output

The total installed global geothermal power capacity reached approximately 16,127 megawatts (MW) by the end of 2022, according to ThinkGeoEnergy. This represents a steady but modest increase over the past decade. In 2009, global geothermal capacity stood at just 10,715 MW.

The countries with the highest installed geothermal capacity are the United States, Indonesia, and Turkey. The United States leads with nearly 3,800 MW of installed capacity, followed by Indonesia with about 2,400 MW. Turkey ranks third with just over 1,600 MW of geothermal capacity.

In terms of electricity generation from geothermal sources, the latest data indicates around 95 terawatt-hours (TWh) was produced globally in 2020. The countries generating the most electricity from geothermal are the United States, Indonesia, and the Philippines. The US produced about 17 TWh in 2020, while Indonesia and the Philippines generated roughly 17 TWh and 10 TWh, respectively.

While growing, geothermal still represents a small fraction of global renewable energy capacity and generation. However, supporters argue geothermal has significant potential for growth if technology improves and barriers related to high upfront costs can be overcome.

Cost of Geothermal

The costs associated with building and operating geothermal power plants can vary greatly depending on the site location and type of plant. Building a geothermal power plant requires high upfront capital costs for exploration, drilling wells, and constructing the power plant facility. According to a 2009 analysis, geothermal power costs average around 3.6 cents per kilowatt-hour to produce, which is competitive with fossil fuel plants.

The initial exploration and test drilling phase makes up about 25-40% of geothermal project costs. Drilling production wells to bring the hot water or steam to the surface accounts for another 35-50% of costs. The geothermal power plant itself represents only about 20% of the total budget. While costly at first, geothermal plants have a typical lifespan of several decades with proper maintenance.

Recent research from UC Berkeley found that geothermal energy provides a higher overall value compared to solar, wind, and solar+storage when accounting for capacity factors, balancing costs, land use, and transmission needs. However, geothermal remains more geographically limited than other renewables. Overall, advances in drilling and plant construction continue to lower geothermal costs and improve its competitiveness.

Challenges and Limitations

While geothermal energy has many advantages, it also comes with some challenges and limitations. One of the biggest is finding ideal sites for geothermal power plants. According to source, geothermal energy is location restricted, so plants need to be built in geothermally active areas near tectonic plate boundaries or hot spots.

Another challenge with geothermal is the risk of seismic activity or earthquakes. As explained by this source, drilling and fracturing rock can destabilize faults and lead to small earth tremors. Proper siting and injection techniques can reduce this risk.

There are also limitations around geothermal reservoir depletion over time. Plants need to actively manage the rate of fluid extraction to prolong the life of the reservoir. Binary power plants that inject the geothermal fluids back underground help address this limitation.

Future Outlook

Geothermal energy has significant potential for future growth globally. According to research from MIT, the potential capacity for geothermal energy could reach 100-200 gigawatts by 2050, up from around 12-15 gigawatts currently. Factors driving this growth include technological innovations, policy support, and increased investment.

Advances in enhanced geothermal systems (EGS) could dramatically increase viable locations and capacity for geothermal energy. EGS involves fracturing underground rock reservoirs to pump water through and produce steam. The US Department of Energy has invested significantly in EGS research and sees it increasing geothermal capacity 10-fold by 2050. Additionally, floating geothermal technology allows offshore access to geothermal reservoirs, further expanding viable locations.

Government incentives like tax credits, loan guarantees, and R&D funding help drive geothermal growth by defraying exploration risk and upfront capital costs. Many countries have set ambitious geothermal targets, including Indonesia’s goal of 7.2 gigawatts of geothermal by 2025. With supportive policies and increased investment, the global geothermal market could reach $6-10 billion annually by 2022.

In summary, geothermal is poised for rapid growth due to technology improvements, supportive government policies, and rising investment – increasing its role in the global renewable energy landscape.

Conclusions

Geothermal energy provides a reliable, sustainable source of renewable power by harnessing heat from the earth’s interior. Key advantages of geothermal power include:

– Geothermal plants emit minimal greenhouse gases and other pollutants compared to fossil fuel plants. This makes geothermal an environmentally friendly energy source.

– Geothermal power is not subject to variable weather conditions like wind and solar power. Geothermal plants provide consistent baseload power 24/7.

– Geothermal energy is renewable and virtually limitless. As long as water can circulate through hot rocks beneath the earth’s surface, we can tap into geothermal heat to generate electricity.

– Geothermal power plants have high capacity factors of 90-95%, compared to 20-35% for solar and wind plants. This results in more reliable and constant electrical output.

– Geothermal energy can be extracted nearly anywhere, providing localized power generation that reduces reliance on transmission lines. Favorable locations with hydrothermal resources exist across continents and countries.

In summary, geothermal power harnesses a sustainable energy source and provides a reliable, clean alternative to fossil fuels for electricity generation worldwide. With continuing innovation and investment, geothermal promises to play an increasing role in the global renewable energy mix.