|
|
| Fig. 1: A geothermal facility in Iceland. (Source: Wikimedia Commons) |
Geothermal Energy transforms heat in the crust of the Earth to energy. Geothermal energy is used by some nations today as a renewable energy source. [1] Some of the methods utilized by geothermal power plants to harness this energy include dry steam, flash, and binary. [2] Dry steam includes trapping steam dissipating from cracks in the ground and using this vapor to turn a turbine. [2] Flash plants pull hot water at high pressure from the ground and expose it to cool water at a lower pressure. [2] The steam from this process is then captured and used to power a turbine. Binary plants involve taking hot water and exposing it to a fluid with a lower boiling point than water. [2] The exposure of the hot water to the secondary fluid causes the secondary fluid to evaporate. This vapor is then used to drive a turbine.
In 2000 electricity generated from geothermal energy made up 0.3 percent of the total world electrical energy. [3] In 2015 governments have only utilized 6.5 percent of global geothermal energy potential with current methods. [2] Both of these findings suggest that geothermal energy production could create more power than it is currently producing. Many countries, such as Iceland, with environments conducive to geothermal energy production aim to increase their use of geothermal energy in the future.
Geothermal reservoirs require specific areas with higher heat flow, permeable rocks, and methods for water to replenish the crust of the Earth. [3] Specific areas with higher heat are required to encourage heat to flow into permeable rocks. These permeable rocks trapped with heat then release the heat as steam when in contact with water. Once heat is released as steam the crust is replenished with water so that more heat can be released from the Earth as steam. In order to replenish the crust with water there must be fractures in the crust so rainwater can descend into areas with higher heat flow and permeable rocks.
In some cases, areas with higher heat flow surround ground water. This water is heated and makes flash plants more useful to generate energy.
Areas naturally prepared for geothermal energy extraction are often found near tectonic plate boundaries where higher heat flow results from an upwelling of the crust-mantle boundary of the Earth. [3]
The geography and weather patterns of Iceland make geothermal energy production a viable energy source for the country. Volcanic activity is common on Iceland as it is located on two tectonic plates that are continually drifting apart from each other. [4] In addition to these factors Iceland's northern latitude results in regular rainfall.
Geothermal energy is a growing renewable energy source in Iceland, with multiple facilities throughout the island (see Fig 1). In 2014, 30 percent of electricity used by the country was powered by geothermal energy. [4] Iceland is currently a leading pioneer in developing this resource. The Iceland Deep Drilling Project has drilled more than 15,000 feet into the Earth's crust towards magma. [6] Researchers working on this project hope to continue developing the site so that it can support a power plant. [6] With developments like the Deep Drilling Project in Iceland, the International Renewable Energy Agency reports that the current contribution of geothermal energy to the world's electricity currently at one percent will increase five times by 2030. [6]
Although geothermal energy has the potential to be a productive renewable energy in Iceland, there are notable drawbacks to the methods used to capture heat from the Earth. Three main concerns include land subsidence, induced seismicity, and pollution of hazardous gas and fluids. [3]
While withdrawing fluids from permeable rocks, the pore pressure of rocks decreases resulting in land subsidence. There is no method to prevent land subsidence due to pressure changes in permeable rocks. In geothermal systems drawing on underground reservoirs it is possible to prevent land subsidence by injecting water into underground reservoirs that have been depleted. This practice, however, may result in tectonic stress and reduced rock stress resulting in seismic activity. Lastly, in the process of obtaining steam or hot water from the Earth's crust hydrogen sulfide is commonly released in low concentrations. [3] Hydrogen sulfide is a colorless poisonous gas. Similar to the release of hydrogen sulfide, geothermal fluids have been found to contain low levels of toxic materials including arsenic, mercury, lead, zinc, boron and sulfur. [3] While these toxins may occur in low levels with enough production of geothermal energy these toxins could begin to accumulate and have more serious impacts.
© Elle Billman. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] G. Sivesind, "Geothermal Energy in Iceland," Physics 240, Stanford University, Fall 2016.
[2] B. Matek, "2015 Annual U.S. and Global Geothermal Power Production Report," Geothermal Energy Association, February 2015.
[3] E. Barbier, Geothermal Energy Technology and Current Status: an Overview," Renew. Sustain. Energy Rev. 6, 3 (2002).
[4] A. Mustain, "Iceland Offers Rare Glimpse of Tectonic Meeting Place," Live Science, 21 Jun 12.
[5] C. Mims, "One Hot Island: Icelands Renewable Geothermal Power," Scientific American, 20 Oct 08.
[6] J. Worland, "A Solution to Our Energy Problem May Lie Right Beneath our Feet," Time, 25 Jul 17.
