Does Geothermal Energy Require A Lot Of Land?

Geothermal energy is heat energy generated and stored within the Earth. The word geothermal comes from the Greek words geo, meaning earth, and therme, meaning heat. Geothermal energy is classified as a renewable energy source because heat is continuously produced inside the Earth by the slow decay of radioactive particles, such as potassium-40 and thorium-232 (https://www.eia.gov/energyexplained/geothermal/). Geothermal energy can be accessed by drilling water or steam wells that tap into these underground heat reservoirs, which are brought to the surface and used to generate electricity or provide heating.

Geothermal Power Plants

There are three main types of geothermal power plant technologies: dry steam, flash steam, and binary cycle [1].

In a dry steam power plant, steam from geothermal reservoirs is piped directly to the power plant where it is directed into a turbine/generator unit to produce electricity. There are only two known dry steam fields in the world: The Geysers in California and Larderello in Italy [2].

Flash steam power plants use geothermal reservoirs of water with temperatures greater than 360°F. The water is pumped under high pressure to the generation equipment at the surface where the pressure is suddenly reduced, converting it into steam to drive the turbines [1].

Binary cycle power plants operate on water at lower temperatures of about 225°-360°F. Heat from the hot water is used to boil a working fluid, usually an organic compound with a low boiling point. The working fluid is vaporized in a heat exchanger and used to turn a turbine [2]. The water and working fluid are kept separated during the whole process, so there are minimal emissions.

Land Requirements

The amount of land needed for geothermal power plants depends on the type of geothermal plant being built. Geothermal power plants that utilize hydrothermal resources, which contain natural reservoirs of steam or hot water, require relatively small land footprints compared to other types of power plants.

According to the Office of Energy Efficiency and Renewable Energy, a 30 megawatt hydrothermal power plant typically needs only about 1-8 acres for the power plant itself [1]. This is because hydrothermal plants can tap directly into existing underground reservoirs and do not require extensive above-ground infrastructure.

In contrast, geothermal plants that rely on enhanced geothermal systems (EGS) require much more land area. EGS plants need to drill multiple deep wells and construct above-ground infrastructure like pipelines and power plants. According to one estimate, an EGS plant generating 100 megawatts would require about 2,000 acres of land [2].

Additionally, geothermal plants require land for supporting infrastructure like access roads and transmission lines. However, when considering total land use requirements, geothermal plants have a much smaller footprint than fossil fuel or nuclear power plants.

Plant Footprint

The actual footprint of a geothermal power plant facility is relatively small compared to other types of power plants. According to the List of geothermal power stations, the largest geothermal power plant in the world is The Geysers in California, which has a capacity of 1,590 MW but occupies only 1.3 square miles of land. In contrast, a 1,000 MW coal plant typically requires over 3 square miles of land.

Most geothermal plants require between just 0.25-1 square miles of land for the power plant facility itself. This compact footprint is because geothermal plants do not need large areas to store fuel like coal and nuclear plants. The main above-ground facilities are the turbine/generator halls, cooling towers, and transformer yards.

So while geothermal energy does require land for drilling wells and reservoirs, the plant footprint itself is relatively small and compact.

Drilling

Geothermal power plants require drilling to access the hot water or steam reservoirs underground that are used to generate electricity. The drilling depth and number of wells needed depends on the type of geothermal resource being utilized.

For hydrothermal resources, wells are drilled down to about 1-2 miles deep to reach permeable zones where hot water can be pumped up to the surface. Multiple production wells are drilled, spaced about 0.5-1 mile apart. Injection wells are also drilled to return the cooled geothermal water underground after passing through the power plant. According to the U.S. Department of Energy, a typical 50 MW hydrothermal plant requires about 16 production and 11 injection wells. The wells occupy about 20 acres total ¹.

Enhanced geothermal systems (EGS), which create reservoirs in hot dry rock, require deeper drilling up to 10,000 feet down. Multiple well pairs are connected via hydraulic fracturing. EGS wells currently occupy about 1 acre per MW capacity, but this could be reduced with advanced drilling techniques ².

Transmission Lines

Geothermal power plants require transmission lines and associated infrastructure to deliver the generated electricity to the grid and end users. According to the U.S. Department of Energy, geothermal transmission lines require about 3 acres per mile of right-of-way (https://www.energy.gov/eere/geothermal/geothermal-basics). This land is needed for the towers, access roads, and a buffer zone around the power lines. The specific amount of land depends on the terrain, existing infrastructure, and distance required to connect to the grid.

One study estimated that a 100 MW geothermal power plant with 25 miles of new transmission lines would use around 75 acres of land for transmission (https://www.lincolninst.edu/publications/articles/2023-06-how-land-use-battles-are-hindering-clean-energy-transition). Compared to other renewable sources like wind and solar PV, geothermal’s transmission land use is relatively small due to the high capacity factors and smaller number of facilities needed. Overall, transmission infrastructure accounts for a small fraction of the total land needs for geothermal power.

Reservoirs

Geothermal power plants use underground reservoirs of hot water as a heat source to produce electricity. The size and depth of these reservoirs can vary greatly, from shallow reservoirs of a few acres to large, deep reservoirs that can span hundreds of square miles. According to the Geothermal Reservoir overview on ScienceDirect, commercial geothermal systems need reservoir areas ranging from 10-100 MW of capacity. These underground reservoirs exist naturally in certain geologic formations.

While geothermal reservoirs can be very large, most of the land surface above them can still be utilized for other purposes like agriculture or recreation. Only the actual geothermal power plant facilities occupy surface land. Drilling into the reservoir occurs at just a single well pad location that takes up a minimal footprint. Overall, geothermal reservoirs require very little surface land area compared to the enormous heating capacity contained underground.

Comparing Land Use

Compared to other renewable energy sources like solar and wind, geothermal power plants generally use much less land. According to a Stanford study, geothermal plants on average require just 1.8 acres per megawatt of installed capacity, versus a range of 5-10 acres per megawatt for wind power and 4-8 acres per megawatt for solar photovoltaic power (1). This is because geothermal plants themselves have a relatively small footprint, and no additional land is needed for fuel harvesting.

While drilling wells and installing pipelines does disturb some land, geothermal systems are able to make very efficient use of vertical space underground. Solar and wind farms, on the other hand, require large contiguous areas of unused land. One analysis found geothermal needing 140 times less land area than solar photovoltaic per unit of electricity generated (2).

Overall, geothermal power can provide the grid reliability and capacity factors of conventional power with a much smaller land footprint than other leading renewable alternatives.

Environmental Impacts

Geothermal power plants can impact the environment in different ways depending on the technology used. Two key environmental concerns are related to air emissions and water consumption/contamination.

Air emissions from geothermal plants are generally lower than fossil fuel plants. However, geothermal reservoirs can contain hydrogen sulfide gas which can be released into the air. Scrubbers are used to remove hydrogen sulfide before venting to reduce air pollution. According to the U.S. Fish and Wildlife Service, hydrogen sulfide emissions are a leading concern with geothermal technologies.1

Geothermal plants use large amounts of water for cooling which is cycled back into reservoirs. This can deplete groundwater resources over time. The used geothermal water also contains chemicals like boron, arsenic, and mercury that can contaminate water sources if not properly disposed of. The U.S. Department of Energy states that proper injection techniques for geothermal fluids are important for protecting groundwater quality.2

Geothermal development may also impact natural habitats and wildlife. Power plants, cooling towers, roads, and pipelines can fragment animal habitats. Noise and traffic from geothermal operations can disturb animals as well. Careful siting of geothermal infrastructure is needed to minimize habitat loss and disruption.

While geothermal energy has lower emissions than fossil fuels overall, there are still important environmental impacts to consider regarding air and water quality, wildlife habitats, and proper management of geothermal reservoirs.

Conclusions

In summary, geothermal power plants do require a substantial amount of land compared to some other renewable energy sources, but not an extraordinary amount compared to traditional power plants. The actual power plant facility footprint is relatively small, but the surrounding land is needed for geothermal fluid reservoirs, wells and drilling pads. Additionally, transmission lines need to be constructed to transport the electricity, requiring right-of-way land acquisition.

That said, geothermal plants enable a high energy output per acre of land used. The environmental impacts are also generally less than traditional fossil fuel plants. While geothermal does have larger land requirements than other renewables like solar or wind, the ability to provide reliable baseload power makes it a valuable clean energy source worth the land needs. Overall, geothermal energy’s land use requirements are reasonable given its advantages as a renewable baseload resource.