Energy 101 for LinkedIn Professionals: Geothermal Energy — Environmental Impacts (3)
As of 2020, our humanity was not able to find a technology that allows causing any changes to the environment. All energy production accompanies some building activity before production and emission issues during the operation phase. Compared to other resources, especially to fossil fuels, a degree of environmental impacts of geothermal energy is rather low. In this article, I will talk about some of the environmental effects of geothermal that are often addressed. The issue associated with induced seismicity is not covered here, as it was covered already in one of my earlier articles.
First of all, let’s talk about greenhouse gas emissions. Greenhouse gas or GHG is known as the cause of the greenhouse effect, which is linked to climate change. When GHG is released from a source, such as a power plant, it remains in the atmosphere. As GHG accumulates in the atmosphere, it creates a layer that prevents heat from the sun to be released to space. Instead, the heat remains within the layer, and as a result, the temperature of the Earth rises. CO2 is the most well-known GHG as humans release it the most compared to the other GHGs. However, water vapor, methane (CH4), nitrous oxide (N2O), and ozone (O3) are also GHG.
Figure 1 — The greenhouse effect of solar radiation on the Earth’s surface caused by greenhouse gases
Anyways, as you can see in Figure 2, geothermal energy emits about the same magnitude as other renewable sources, and far less than fossil fuels. Good evidence of its low-emission capability can be seen in Iceland. Iceland is one of the countries that heavily rely on geothermal energy for its electricity. For instance, 53% of the country’s electricity comes from geothermal energy. Still, only 5% of the GHG gas emissions are from the production of geothermal energy.
Figure 2 — Greenhouse gas emissions from various types of energy sources during the generation of electricity
Another significant emission issue related to geothermal energy is related to hydrogen sulfide (H2S). H2S concerns a lot of people, not only because it smells like rotten eggs, but it is also poisonous, corrosive, and flammable. The concern is understandable, as enough dosage of H2S can kill a person. However, according to the U.S. Office of Energy Efficiency & Renewable Energy, typical emissions of H2S from geothermal power plants are less than 1 part per billion or 0.001 part per million. Note that the lethal dosage limit of H2S is around 100 ppm. 1 ppb of H2S is not concentrated enough for a person to smell its unpleasant odour. For a big plant such as The Geysers in California, the U.S., more than 99.9 percent of H2S from the steam is removed by a series of treatment processes, before it is released into the atmosphere.
Water-related issues are also important considerations for geothermal power plants. In terms of water quality, the two major issues are ground/surface water temperature change and leakage of contaminated water into the groundwater-bearing aquifer. For the first issue, if hot water is released into the environment from a geothermal power plant, it also raises the temperature of the water where it is released to. For surface water bodies like a lake, river, and nearshore seawater, the inhabitants can be affected negatively. Also, for groundwater, the increased water temperature can stimulate chemical reaction between the groundwater and the minerals in the subsurface, and impact the groundwater quality. To prevent unwanted consequences, many power plants use cooling towers or air-cooled condensers (Figure 3), to reject waste heat into the atmosphere from the working fluid. By doing this, it can minimize the impact of releasing hot water, even better than most fossil fuel and nuclear power plants.
Figure 3 — Cooling tower of a geothermal power plant
The leakage issue has been one of the main problems for subsurface operations, including oil and gas, wastewater disposal, carbon capture, and sequestration (CCS), etc. The problem with the leakage is caused by cracks and small gaps that act as conduits for injected water. The best strategy to remediate the issue should be taken before the construction of geothermal wells. The geothermal wells have to be lined with steel or titanium casing, and cement is added to separate injected fluid from the surrounding environment completely. Once the operation commences, rigorous monitoring effort should be put in. Popular monitoring options that are often deployed in geothermal power plants include continuous examination using geophysics-based sonic logging instruments and videography. These technologies allow identification of leaking spots along the well so that the problem can be fixed promptly.
There are other environmental concerns associated with a geothermal power plant, such as noise and sight pollution, soil subsidence, odours, water usage, etc. However, these risks of arousing these concerns much lower, as they are typically mitigated from the planning stage. The best planning strategy for geothermal power plant constructions, or any other major infrastructure construction, is to avoid its interference with human and other inhabitants. If that is not possible, alternative strategies may be implemented that are supported by technologies and rigorous monitoring efforts. Once the risks are all well-managed, geothermal energy can definitely play a significant role in the clean energy future.
Figure 4 — Various applications of geothermal energy
References
Academic sources:
Ragnarsson, Á., 2001. Energy consumption in Iceland (in Icelandic). Orkuþing 2001, Gunnarsdóttir, M. J. (Ed.), Reykjavı́k, 45–52.
Hallsdóttir, B., 2001. Emission of air polluting substances and accounting of emissions (in Icelandic). Orkuþing 2001, Gunnarsdóttir, M.J. (Ed.), Reykjavı́k, 308–316.
Online sources:
https://en.wikipedia.org/wiki/Greenhouse_gas https://www.energy.gov/eere/geothermal/geothermal-power-plants-meeting-clean-air-standards https://www.energy.gov/eere/geothermal/geothermal-power-plants-meeting-water-quality-and-conservation-standards Image sources:
2. Hunt, T., 2001. Five lectures on environmental effects on geothermal energy utilization. United Nations University Geothermal Training Programme 2000, Report 1, Reykjavı́k, Iceland, pp. 109.
2. Ármannsson, H., Kristmannsdóttir, H., Hallsdóttir, B., 2001. Gas emissions from geothermal fields (In Icelandic). Orkuþing 2001, Gunnarsdóttir M. J. (Ed.), Reykjavı́k, pp. 324–330.
3. Environmental and Industrial Corrosion — Practical and Theoretical Aspects. (2012). doi: 10.5772/45617
4. Canadian Geothermal Energy Association (CanGEA) ( https://www.cangea.ca/)
Originally published at https://www.linkedin.com.
