Geothermal energy is a clean source of renewable electricity with a significantly lower environmental impact than more conventional energy sources like fossil fuels. With the issue of climate change and global warming caused by burning fossil fuels, many individuals and industries are tilting to more renewable sources for energy use.
On a global scale, geothermal power is largely untapped. Experts consider geothermal plants more sustainable than fossil fuel power plants because they do not require fossil fuel burning to generate geothermal energy.
While geothermal power is a form of renewable energy, it isn’t exactly limitless. There are limited locations on the earth that are suitable for constructing geothermal power plants.
Read on as we examine the environmental impacts of geothermal energy.
Geothermal power is a renewable energy source from heat captured within rocks and fluids from the earth’s core. The heat primarily results from the continuous process of radioactive decay of uranium, potassium, and thorium in the earth’s interior. The heat from the earth’s interior generates geothermal fluids like lava, geysers, hot springs, mud pots, and so on.
The amount of energy from geothermal resources can vary depending on the extraction method and depth.
Within the earth, the temperature rises with depth. It can become magma when temperatures go as high as 700 - 1300 degrees Celsius. The magma then heats rocks nearby, which sometimes causes the release of hot water in the form of mud pots, hot springs, and steam vents.
Energy producers can capture this heat and use it to generate electricity or heat buildings, pools, sidewalks, and other structures. However, most of the earth’s energy may not emerge as magma, steam, or water. Instead, it remains in mantles emanating as small pockets of high heat.
Manufacturers have to extract dry heat by drilling. Heated fluids from a geothermal resource are drilled and extracted to the surface. The steam and water generated are then connected through pipelines to a geothermal power plant to generate electricity.
In countries like Iceland, there are many sources of geothermal hot water, making geothermal power a dependable renewable energy source. In other countries like the United States, generating geothermal power involves drilling and is more expensive.
A geothermal plant has three major designs: the dry steam power plant, the flash steam power plant, and the binary cycle power plant.
The dry steam power plant is the oldest type of plant used for power generation. The power plant gets its steam from natural underground sources of steam for electricity. The steam then gets piped to a power plant, which spins turbines to produce electricity.
Two sources of underground steam are found in the US where the dry steam plants are used. These sources occur in the form of Geysers at Yellowstone National Park and in California.
Flash steam power plants are the most commonly used type of geothermal power plant. Natural sources of underground steam and heated water get pumped to a low-pressure area. Next, the water evaporates rapidly into steam which manufacturers funnel out to power turbines for electricity.
In Iceland, most electricity produced comes through flash steam power plants.
Binary cycle power plants use a process that generates heat and conserves water1. Firstly, manufacturers heat water underground to a temperature of 107°-182° C or 225°-360° F.
A pipe that cycles above the ground encloses the heated water. The heated water heats an organic compound at a boiling point lower than water. The organic liquid formed then flows through a turbine which powers a generator to produce electricity. Binary cycle power plants produce no greenhouse gas emissions except waste heat.
Once electricity is produced, the water is recycled into the ground to be reheated by the earth, and the cycle continues.
Experts say geothermal power is clean energy that is more cost-effective and efficient than burning fossil fuels4. Geothermal power plants have a smaller carbon footprint than coal plants and other fossil fuel power plants that burn gas or other finite resources.
To measure the environmental impacts of various energy sources, we can analyze the life cycle of greenhouse gas emissions which is the total amount of greenhouse gases measured in grams of carbon dioxide equivalent or gCOeq/kWh.
A life cycle analysis considers the environmental cost of obtaining raw materials, the manufacturing processes, operations, and end-of-life waste management.
Reports from the Intergovernmental Panel on Climate Change (IPCC) in 2014 examined the life cycle emissions of different electricity generation plants, including renewable energy sources and fossil fuels. The report measures these emissions per kilowatt-hour of energy for different power plants.
The life cycle analyses of Geothermal power plants3 found emissions of 38gCOeq/kWh, which was 95% less than coal 820 grams carbon dioxide equivalent per kilowatt hour (820gCOeq/kWh) and 92% less than natural gas 490 grams carbon dioxide equivalent per kilowatt hour (490gCOeq/kWh).
Geothermal plants have different methods of converting and cooling geothermal resources into electricity, with the environmental impacts depending mainly on the method. Let’s dive into the impacts of geothermal energy on the environment.
We need to look at open and closed-loop systems when considering air emissions. With closed-loop systems, manufacturers inject the gases emanating from gas wells back into the ground, ensuring that air emissions are minimal.
On the other hand, the open loop systems release gases like carbon dioxide, methane, ammonia, and hydrogen sulfide, which is the most common of all the gases, according to a guide to geothermal energy and the environment by the Geothermal Energy Association6.
When hydrogen sulfide is released into the atmosphere, it changes to sulfur dioxide, contributing to the formation of acidic particles. According to the National Research Council, our bloodstream can absorb these particles causing human harm5. It also contributes to the formation of acid rain, which damages crops, forests, lakes, and streams.
Geothermal power plants can have a significant impact on water consumption and water quality. Water that comes from underground reservoirs comes with high amounts of minerals like sulfur and salts.
Most geothermal facilities use closed-loop systems, which means that manufacturers pump extracted water back into geothermal reservoirs after heat and power production, typically enclosing it in a suitable casing made of steel. According to the National Renewable Energy Laboratory, In the United States, there are no cases of water contamination from geothermal sites7.
Apart from this, plants also need water for re-injection and cooling. Most geothermal plants use geothermal waters or freshwater. Using geothermal water or fluids instead of fresh water can decrease the water impact of geothermal power plants.
Also, a geothermal power plant re-injects water into a geothermal reservoir to prevent land subsidence and contamination. Most times, during the process of re-injection, water gets lost as steam. To maintain a constant water volume, water is needed externally. The amount required will depend on the size of the geothermal power plant and the technology employed. However, most geothermal power facilities use dirty water for the process.
The land size needed by a geothermal plant depends on several factors, including the type of energy conversion, the amount of power capacity, piping systems, and the arrangement of wells. Typically, you can find geothermal sites in remote areas; a consideration for developers when embarking on geothermal projects.
When it comes to land use, there is the issue of land subsidence caused by removing water from geothermal reservoirs, which occurs when the land surface sinks. Most facilities take care of this by re-injecting wastewater back into reservoirs.
Sadly, enhanced geothermal systems or hot, dry rock can escalate the risk of small earthquakes. The process involves pumping water into cracked underground hot rock reservoirs at high pressures. However, suppliers can minimize earthquake risks by installing geothermal power plants far from major fault lines. If geothermal systems are planted close to highly populated locations, constant monitoring and communication with local communities are essential.
Meanwhile, innovative approaches are exploring the use of abandoned oil wells to capture geothermal energy2. This method further helps to seal and reuse land already degraded by fossil fuel extraction.
As with most traditional and renewable sources of energy, there are also environmental downsides to geothermal energy.
Land subsidence is one of the main concerns of geothermal development and power plant construction. As plants remove water and steam from underground reservoirs, the land begins to sink over time, altering vegetation and wildlife.
However, most geothermal plants reinject geothermal waters back into the earth to reduce this. Geothermal energy is location-dependent. This means building geothermal power plants where energy is easily accessible.
Another environmental downside to geothermal power is the increased risk of small earthquakes. Drilling exploratory wells searching for geothermal potential near fault lines can increase the risk of earthquakes. Geothermal plants also release some greenhouse gases like hydrogen sulfide during drilling. However, these gases have lower emissions when compared to fossil fuels.
The process needs appropriate management for the sustainable development of geothermal energy.
With proper management, geothermal power plants can last for decades or even centuries. Geothermal energy is always accessible and is not dependent on weather-changing factors like the sun or wind. Although geothermal power has a few downsides, like land subsidence and risks of small earthquakes, energy suppliers can curb these challenges using more sustainable methods.
Alessandro Franco, Marco Villani, Optimal design of binary cycle power plants for water-dominated, medium-temperature geothermal fields, Geothermics, Volume 38, Issue 4, 2009, Pages 379-391, ISSN 0375-6505, https://doi.org/10.1016/j.geothermics.2009.08.001
Wen-Long Cheng, Tong-Tong Li, Yong-Le Nian, Kun Xie, An Analysis of Insulation of Abandoned Oil Wells Reused for Geothermal Power Generation, Energy Procedia, Volume 61, 2014, Pages 607-610, ISSN 1876-6102, https://doi.org/10.1016/j.egypro.2014.11.1181
Bruckner T., I.A. Bashmakov, Y. Mulugetta, H. Chum, et, al., 2014: Energy Systems. In: Climate Change 2014: Mitigation of Climate Change (pdf). Contribution of Working Group III to the
Paul Brophy, Environmental advantages to the utilization of geothermal energy, Renewable Energy, Volume 10, Issues 2–3, 1997, Pages 367-377, ISSN 0960-1481, https://doi.org/10.1016/0960-1481(96)00094-8
Auffhammer M. Hidden Costs of Energy: Unpriced Consequences of Energy Production and Use. Environ Health Perspect. 2011 Mar;119(3):A138. PMCID: PMC3060022.
Kagel, A. 2007. A Guide to Geothermal Energy and the Environment. Washington, DC: Geothermal Energy Association.
National Renewable Energy Laboratory. (2012). Renewable Electricity Futures Study. Hand, M.M.; Baldwin, S.; DeMeo, E.; Reilly, J.M.; Mai, T.; Arent, D.; Porro, G.; Meshek, M.; Sandor, D. eds. 4 vols. NREL/TP-6A20-52409. Golden, CO: National Renewable Energy Laboratory. http://www.nrel.gov/analysis/re_futures/.
Jen’s a passionate environmentalist and sustainability expert. With a science degree from Babcock University Jen loves applying her research skills to craft editorial that connects with our global changemaker and readership audiences centered around topics including zero waste, sustainability, climate change, and biodiversity.
Elsewhere Jen’s interests include the role that future technology and data have in helping us solve some of the planet’s biggest challenges.