The Main Pros and Cons of Geothermal Energy
Geothermal reservoirs are locations where rock layers heated by the earth's core are located closer to the surface than in other areas. This provides accessibility and we have the ability to create power by harnessing water and steam created within the earth and pumped or siphoned to the surface.
By either pumping cold water down several miles to be heated by rock or by pumping heated water to the surface, we can power turbines and generators and create a reliable power source. The existence of deep reservoirs of heated water has been known and utilized in many areas of the globe. Hot springs and geysers pinpointed locations of underground reservoirs in the past.
Today, advanced imaging techniques can be used to find geothermal reservoirs and even to estimate the volume of water contained. This has led to some interesting finds such as a huge body of ancient water far below the surface of the Sahara desert.
Geothermal energy can only be used in locations where the topography of the earth provides reservoirs. In these areas, the magma (molten rock) comes closer to the surface and the water running through this porous and fractured rock creates a hydrothermal feature. Hydrothermal refers to the presence of water and heat. Geothermal reservoirs are found by geologists who drill test holes deep into the ground to find existing geothermal reservoirs.
Most of the geothermal resources in the U.S. are located in Western states and in Hawaii. California is the main source of most geothermal electricity. The Geysers dry steam reservoir in northern California is the largest of its kind in the world and power plants have been producing electricity from that natural geothermal reservoir since 1960.
Tapping fluids trapped deep in the earth releases gases such as carbon dioxide, hydrogen sulfide, methane and ammonia. These are pollutants which can cause acid rain, noxious odors and are considered one of the causes of global warming.
The release of the gases is far less than the emissions produced by producing electricity through burning of fossil fuels. With geothermal electricity product, emission control systems reduce the exhaust of gases to safe levels.
Water that produces geothermal energy can also contain toxic elements like boron, arsenic and mercury. These chemicals separate as the heated water is cooled and would damage the environment if released. Today, geothermal power plants avoid this hazard by injecting the cooled (used) fluids back into the earth where they came from.
Construction of geothermal plants can have a negative effect on the stability of the land surrounding the reservoir. The construction involves drilling deep wells miles into the earth's surface and that drilling has been linked to triggering earthquakes caused by hydraulic fracturing. On a few occasions, construction of a geothermal power plant has been halted when water injected to the hot rocks resulted in numerous seismic events.
When considering pros of geothermal energy the limited requirement for using land and fresh water in the generating process is a huge plus. A geothermal power plant needs about 1.4 square miles of land to product one gigawatt of electrical power while coal facilities require 12 square miles of land and wind farms need 4.6 square miles to yield the same amount of power.
Fresh water usage for a geothermal energy power plant is about 20% of the water necessary for operating nuclear, coal or oil fired power plants. Hot springs have been used since Paleolithic times and the oldest spa known was located in China in the 3rd century BC. Over the centuries, hot springs have become famous as public baths and reputed to be a source of health and healing.
The first commercial ventures into geothermal energy were the public baths where fees were charged. In areas where hot springs were widespread, the naturally heated water was routed under the floors of buildings to provide natural warmth.
In the U.S., the first public heating system in Boise, Idaho was powered directly by geothermal energy in 1892 and used in Oregon in 1900. Deep geothermal wells produced hot water to heat greenhouses and the invention of heat exchangers allow hot spring and geysers to provide home heating in Iceland beginning in 1943. The heat pump now used in so many home HVAC systems was developed to capture and use geothermal energy.
How it Works
Rain and snow flow into the ground and seep deep into the earth. When the water reaches heated rocks miles below the surface the steam and hot water produced flow into underground reservoirs. This happens only in locations where the geologic conditions permit.
These reservoirs are mostly located in areas where the tectonic plates meet. This fractured series of rocks allows underground water to flow into deep reservoirs but the same features also form the fault lines of earthquake prone areas.
The hottest geothermal regions known in the world are referred to as the Ring of Fire and, not surprisingly, that ring following the major fault lines around the edge of the Pacific Ocean. Accessing the deep, heated water and steam requires significant drilling deep into the rock beds and that drilling has the potential for disturbing the balance of the tectonic plates and leading to increased seismic activity in the region or in being transmitted to another area along the same fault lines.
Geothermal energy can reduce our dependence on fossil fuels and avoid the consequences to the environment that are common to use of oil, gas and nuclear energy production. In other words, it is a great alternative energy resource we can rely on!
The science of geothermal energy production and seismology go hand in hand. As we better understand the fault lines produced by moving tectonic plates, we will better be able to create electricity using natural geothermal energy.