What is geothermal energy and how does it work?

Geothermal energy is a renewable energy source that harnesses the Earth’s internal heat to generate electricity or provide heating. Unlike solar or wind energy, geothermal energy offers a consistent and reliable output regardless of weather conditions. In the United States, geothermal energy already plays an important role in states like California and Nevada, and its potential for expansion continues to draw interest from the energy sector and policymakers.

This type of energy is stored underground in the form of hot water or steam. With the right technologies, this heat can be extracted and converted into usable energy for residential, commercial, and industrial applications. Geothermal energy is considered clean, efficient, and sustainable, contributing to the reduction of greenhouse gas emissions and supporting the country’s goal of transitioning to a low-carbon economy.

Several U.S. government agencies, including the Department of Energy (DOE), actively support geothermal research and infrastructure development. Understanding how geothermal energy works, its benefits, limitations, and current status in the U.S. is essential for recognizing its role in the country’s energy future.

The Origin and Use of Earth’s Internal Heat

The heat used to generate geothermal energy comes from two primary sources: the residual heat from the Earth’s formation over 4.5 billion years ago, and the ongoing radioactive decay of elements such as uranium, thorium, and potassium deep within the planet’s mantle.

In the U.S., geothermal hotspots are primarily found in the western states, particularly near tectonic plate boundaries and volcanic areas. These include parts of California, Nevada, Utah, Oregon, and Idaho. In these regions, underground temperatures can exceed 400°F (200°C) at accessible depths, making them ideal for geothermal power generation.

To tap into this heat, engineers drill wells deep into the Earth’s crust to access underground reservoirs of hot water or steam. Once brought to the surface, this thermal energy can be used directly for heating or converted into electricity through various types of geothermal power plants.

The U.S. has a long history of utilizing geothermal heat, dating back to Native American use of hot springs and expanding into modern industrial and residential applications. Today, ongoing research seeks to identify new geothermal fields and improve the efficiency and reach of current technologies.

How Geothermal Energy Works

The process of generating geothermal energy begins with locating a viable geothermal resource. These are underground reservoirs where water or steam is naturally heated by the Earth’s core. In the U.S., this is typically done using geological surveys and advanced seismic and thermal imaging technologies funded in part by the Department of Energy.

Once a resource is identified, wells are drilled to bring the hot fluid to the surface. Depending on the type of plant and the temperature of the resource, the process varies. In dry steam plants, steam is directly piped to a turbine that drives a generator. In flash steam plants, high-pressure hot water is depressurized (“flashed”) to produce steam for power generation. On binary cycle plants, the geothermal water heats a secondary fluid with a lower boiling point, which vaporizes and powers a turbine.

After its energy is used, the cooled water or condensed steam is re-injected into the ground through another well. This helps maintain reservoir pressure and ensures the sustainability of the system.

Geothermal energy in the U.S. is also used in direct-use applications such as district heating systems, greenhouses, aquaculture facilities, and spa resorts. Additionally, geothermal heat pumps (GHPs) are becoming increasingly popular for heating and cooling homes, even outside geothermally active regions.

Types of Geothermal Power Plants and Applications

There are three main types of geothermal power plants, each suited to different geologic and thermal conditions: dry steam, flash steam, and binary cycle. These technologies allow flexibility in adapting geothermal systems to a wide range of environments.

Dry steam plants are the oldest and simplest. They use steam that comes directly from underground to turn turbines and generate electricity. This method is only viable where steam resources exist naturally, as found in places like The Geysers in Northern California, the largest dry steam field in the world.

Flash steam plants are more common and work with underground water that exceeds 360°F (180°C). When this high-pressure water rises to the surface, it flashes into steam due to the drop in pressure. The steam is then separated and used to spin a turbine. Leftover water can be recycled back into the reservoir.

Binary cycle plants are the most versatile and suitable for moderate-temperature resources (between 225°F and 360°F). These systems use geothermal water to heat a secondary liquid with a lower boiling point, which vaporizes and drives the turbine. Binary cycle technology is increasingly used in U.S. locations with lower-temperature resources.

Beyond electricity generation, geothermal energy supports numerous direct applications. In the United States, cities like Boise, Idaho use district heating systems powered by geothermal wells. Greenhouses in New Mexico, aquaculture farms in Oregon, and spas across the western states also benefit from geothermal heat. The growing use of geothermal heat pumps in residential and commercial buildings underscores the adaptability of this technology.

Advantages of Geothermal Energy Over Other Sources

Geothermal energy offers several distinct advantages that position it as a key player in the renewable energy sector. One of the greatest strengths of geothermal energy is its reliability. Unlike solar or wind energy, which depend on weather conditions, geothermal energy can provide baseload power—consistent electricity 24 hours a day, 365 days a year.

Another major benefit is its low environmental impact. Geothermal power plants emit very low levels of greenhouse gases compared to fossil fuel plants. Additionally, the land footprint of geothermal facilities is much smaller than that of solar farms or wind parks, making them less disruptive to ecosystems.

Geothermal systems are also known for their high efficiency. Once a geothermal power plant is operational, its running costs are relatively low. The technology has long lifespans and minimal fuel requirements, which translates into stable electricity prices and long-term energy security.

From an economic standpoint, geothermal energy can create local jobs in drilling, construction, plant operations, and maintenance—especially in rural areas where many geothermal resources are located. It also reduces dependence on imported fuels and enhances national energy independence.

As states work to meet clean energy targets under frameworks like the Inflation Reduction Act and various state-level Renewable Portfolio Standards (RPS), geothermal energy stands out as a reliable and sustainable solution.

Disadvantages and Current Limitations

Despite its advantages, geothermal energy in the U.S. faces several challenges that have slowed its wider adoption. First, the upfront capital costs for geothermal development are high. Drilling wells, conducting resource assessments, and building power plants require significant investment before any return is seen.

Geographic limitations also play a role. Most geothermal resources in the U.S. are located in the West, which limits their accessibility to other regions unless transmission infrastructure is expanded. While technologies like Enhanced Geothermal Systems (EGS) aim to address this, they are still under development and not yet commercially widespread.

There are also technical and environmental risks. Improper drilling can lead to minor seismic activity, and there is a risk of contaminating groundwater if not managed correctly. However, with modern regulations and careful project planning, these risks can be minimized.

Another barrier is the lack of public awareness and policy prioritization. While wind and solar have received widespread support and incentives, geothermal has historically been underfunded by comparison. This has hindered the growth of the geothermal sector and delayed technological innovation.

To fully realize geothermal energy’s potential, the U.S. must invest in R&D, streamline permitting processes, and establish a clearer regulatory framework that promotes private investment and public confidence in the technology.

Geothermal Energy in the U.S.: Current Status and Outlook

The United States is the world’s leading producer of geothermal electricity, with a total installed capacity of over 3,700 megawatts (MW) as of 2024. Most of this capacity is located in California, particularly in The Geysers field, which alone accounts for over 1,500 MW. Other states like Nevada, Utah, Oregon, and Idaho also contribute significantly to national output.

Recent years have seen a revival in interest thanks to federal initiatives and new investments. The U.S. Department of Energy has launched the GeoVision roadmap to explore pathways for expanding geothermal energy use by more than 26-fold by 2050. This includes not only electricity generation but also heating and cooling via geothermal heat pumps and direct-use systems.

Private sector activity is also increasing. Companies like Fervo Energy and Eavor are pioneering Enhanced Geothermal Systems (EGS) that aim to unlock geothermal resources in areas previously thought unfeasible, including parts of Texas, Colorado, and even the Appalachian region.

State-level policies are beginning to support geothermal integration. For instance, Nevada’s Renewable Portfolio Standard includes geothermal energy as a priority source, and Utah’s Intermountain Power Project is exploring hybrid systems that combine geothermal with hydrogen and solar power.

If these trends continue, geothermal energy could play a central role in the U.S. energy transition, providing clean, reliable, and American-made power for decades to come.

The Global Future of Geothermal Energy

Globally, geothermal energy is gaining recognition as a key component of the renewable energy mix. Countries such as Iceland, Kenya, Indonesia, and the Philippines are already generating a significant portion of their electricity from geothermal resources. These examples prove that, with proper investment and policy support, geothermal can scale effectively.

Innovations like Enhanced Geothermal Systems and closed-loop technologies are expanding the potential footprint of geothermal worldwide. These advances allow heat extraction from areas without naturally occurring water reservoirs or porous rock formations, opening opportunities in regions previously deemed unsuitable.

In the context of climate change, geothermal energy’s baseload capability makes it especially valuable. It can stabilize grids dominated by variable renewables and reduce reliance on fossil fuels during peak demand. This makes it an excellent complement to solar and wind power.

International organizations, including the International Renewable Energy Agency (IRENA) and the World Bank, are actively supporting geothermal development through funding, research, and policy guidance. The United States, with its technical expertise and existing infrastructure, is well positioned to lead these global efforts.

As governments worldwide strive for energy independence and decarbonization, geothermal energy stands out as a practical and promising solution.

Frequently Asked Questions (FAQ)

1. What makes geothermal energy different from other renewables?
Unlike solar or wind, geothermal energy can generate power continuously, regardless of weather or daylight, providing consistent baseload electricity.

2. Can geothermal energy be used in homes?
Yes. Geothermal heat pumps are widely used in residential and commercial buildings across the U.S. for highly efficient heating and cooling.

3. Is geothermal energy environmentally friendly?
Yes. It produces very low emissions and has a small land footprint. Closed-loop systems and fluid reinjection help minimize any environmental impact.

4. Where in the U.S. is geothermal energy most developed?
California, Nevada, Utah, Oregon, and Idaho are the leading states, but newer technologies may expand its use to other regions.

5. What’s needed to grow geothermal energy in the U.S.?
Increased funding, better public awareness, supportive policies, and continued investment in new technologies like Enhanced Geothermal Systems.