Geothermal Energy Pros and Cons

Krafla geothermal power plant aerial view Northeastern Iceland Scandinavia
Krafla geothermal power plant in northeastern Iceland. naumoid / Getty Images

As a relatively clean and sustainable alternative to traditional sources of energy, geothermal energy plays an important role in gaining independence from non-renewable resources like coal and oil. Not only is geothermal energy incredibly abundant, it is extremely cost effective when compared to other popular forms of renewable energy. 

As with other energies, though, there are some downsides that must be addressed in the geothermal energy sector — like the potential for air and groundwater pollution. Still, when balancing geothermal energy pros and cons, it’s apparent that it provides an appealing, accessible, and reliable source of power.

What Is Geothermal Energy?

Taking its power from Earth’s core, geothermal energy is generated when hot water is pumped to the surface, converted into steam, and used to rotate an aboveground turbine. The motion of the turbine creates mechanical energy that is then converted into electricity using a generator. Geothermal energy can also be harvested directly from underground steam or using geothermal heat pumps, which use the warmth of the Earth to heat and cool homes.

Advantages of Geothermal Energy

As a relatively clean and renewable source of energy, geothermal energy has a number of advantages over traditional fuels like oil, gas, and coal.

It’s Cleaner Than Traditional Sources of Energy

The extraction of geothermal energy doesn’t require the burning of any fossil fuels like oil, gas, or coal. Because of this, geothermal energy extraction produces only one-sixth of the carbon dioxide produced by a natural gas power plant that’s considered relatively clean. What’s more, geothermal energy produces little to no sulfur-bearing gasses or nitrous oxide.

A comparison of geothermal energy to coal is even more impressive. The average coal power plant in the U.S. produces about 35 times as much CO2 per kilowatt-hour (kWh) of electricity as what's emitted by a geothermal plant. 

Geothermal Energy Is Renewable and Sustainable

In addition to producing a cleaner form of energy than other alternatives, geothermal energy is also more renewable and, therefore, more sustainable. The power behind geothermal energy comes from the heat of the Earth’s core, making it not only renewable, but practically unlimited. In fact, it’s estimated that less than 0.7% of the geothermal resources in the United States have been tapped.

Geothermal energy taken from hot water reservoirs is also considered sustainable because the water can be reinjected, reheated, and reused. For example, in California, the City of Santa Rosa recycles its treated wastewater as reinjection fluid through The Geysers power plant — resulting in a more sustainable reservoir for the production of geothermal energy.

What’s more, access to these resources will continue to expand with the development of enhanced geothermal system (EGS) technology — a strategy that involves injecting water into deep rocks to reopen fractures and increase the flow of hot water and steam into extraction wells.

The Energy Is Abundant

Geothermal energy stemming from the Earth’s core can be accessed practically anywhere, making it incredibly abundant. Geothermal reservoirs within one or two miles of Earth’s surface can be accessed via drilling and, once tapped, are available all day, every day. This stands in contrast to other forms of renewable energy, like wind and solar, which can only be captured under ideal circumstances. 

It Only Requires a Small Land Footprint

Compared to other alternative energy options, like solar and wind, geothermal power plants require a relatively small net amount of land to produce the same amount of electricity. On average, a geothermal power plant only requires around 7 square miles of surface land per terawatt hour (TWh) of electricity. To yield the same output, a solar plant requires between 10 and 24 square miles, and a wind farm needs 28 square miles.

Geothermal Power Is Cost Effective

Because of its abundance and sustainability, geothermal energy is also a cost effective alternative to more environmentally destructive options. Electricity generated at The Geysers, for example, is sold at $0.03 to $0.035 per kWh. On the other hand, according to a 2015 study, the average cost of energy from coal power plants is $0.04 per kWh; and the savings is even higher when compared to other renewables like solar and wind, which typically cost around $0.24 per kWh and $0.07 per kWh, respectively. 

It’s Supported by Continuing Innovation

Geothermal energy also stands out because of the continuing innovation that makes the power source even more abundant and sustainable. Generally speaking, the amount of energy produced from geothermal plants is expected to balloon to just over 52 billion kWh in 2050 — up from 16 billion kWh in 2019. The continued use and development of EGS technology is also expected to expand the geographic feasibility of geothermal energy harvest. 

Harnessing Geothermal Energy Yields Valuable Byproducts

The harnessing of geothermal steam and hot water to generate power produces another byproduct — solid waste like zinc, sulfur, and silica. This was historically considered a disadvantage because the materials needed to be properly disposed of in approved sites, which added to the costs of converting geothermal energy into useful electricity. 

Luckily, some of the valuable byproducts that can be recovered and recycled are now intentionally extracted and sold. Even better — solid waste production is typically so low that it doesn’t significantly impact the environment. 

Disadvantages of Geothermal Energy

geothermal plant
Card76 / Getty Images

Geothermal energy has a number of advantages over less renewable options, but there are still negatives stemming from financial and environmental costs, like high water usage and the potential for habitat degradation.  

Requires High Initial Investment

Rather than requiring high operation and maintenance costs, geothermal power plants require a high initial investment — around $2,500 per installed kilowatt (kW). This stands in contrast to about $1,600 per kW for wind turbines, making geothermal energy more costly than some alternative energy options. Importantly, though, new coal power plants can cost as much as $3,500 per kW, so geothermal energy is still a cost-effective option in spite of its high capital requirements. 

Geothermal Energy Has Been Linked to Earthquakes

Geothermal power plants generally reintroduce water into thermal reservoirs via deep well injection. This enables plants to dispose of the water utilized in energy production while maintaining the sustainability of the resource — water that is reinjected can be reheated and used again. EGS also requires injection of water into wells in order to expand fractures and increase energy production. 

Unfortunately, the process of injecting water via deep wells has been linked to increased seismic activity in the vicinity of these wells. These mild tremors are often referred to as micro-earthquakes, and often aren’t noticeable. For example, the U.S. Geological Survey (USGS) records around 4,000 earthquakes above magnitude 1.0 in the vicinity of The Geysers each year — some of which register as high as 4.5.

Production Uses a Large Volume of Water

Water use can be an issue with both traditional geothermal energy production and EGS technology. In standard geothermal power plants, water is drawn from underground geothermal reservoirs. While excess water is generally injected back into the reservoir via deep well injection, the process can result in an overall lowering of local water tables. 

Water consumption is even higher for producing electricity from geothermal energy via EGS. This is because large volumes of water are necessary for drilling wells, constructing wells and other plant infrastructure, stimulating injection wells, and otherwise operating the plant. 

Can Cause Air and Groundwater Pollution

Though less damaging to the environment than drilling for oil or mining coal, harnessing geothermal energy can lead to degraded air and groundwater quality. Emissions primarily consist of carbon dioxide, a greenhouse gas, but this amounts to much less damage than fossil fuel plants producing a similar amount of energy. Groundwater impacts are due in large part to the additives used to avoid deposition of solids on expensive equipment and drill casings. 

What’s more, geothermal water often contains total dissolved solids, fluoride, chloride, and sulfate at levels that exceed primary and secondary drinking water standards. When this water is converted to steam — and ultimately condensed and returned underground — it can result in air and groundwater pollution. If a leak occurs in an EGS, contamination can reach even higher concentrations. Finally, geothermal power plants may result in emissions of elements like mercury, boron, and arsenic, but the impacts of these emissions are still being studied.

Has Been Linked to Altered Habitats

In addition to having the potential for air and groundwater pollution, geothermal energy production can lead to habitat destruction in the vicinity of well sites and power plants. Drilling into geothermal reservoirs can take several weeks and requires heavy equipment, access roads, and other infrastructure; as a result, the process can disturb vegetation, wildlife, habitats, and other natural features. 

Requires High Temperatures

In general, geothermal power plants require fluid temperatures of at least 300 degrees Fahrenheit, but can be as low as 210 degrees. More specifically, the temperature required to harness geothermal energy varies depending on the type of power plant. Flash steam plants require water temperatures over 360 degrees Fahrenheit, while binary cycle plants typically only need temperatures between 225 degrees and 360 degrees Fahrenheit.

This means that geothermal reservoirs not only need to be within one or two miles of Earth’s surface, they must be located where the water can be heated by magma from Earth’s core. Engineers and geologists identify possible locations for geothermal power plants by drilling test wells to locate geothermal reservoirs.

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