Inside the Earth The earth’s interior has layers of hot rock that can serve as an abundant and mostly renewable resource. In fact, the earth’s inner core can reach temperatures of up to 4500 degrees Celcius!
Sometimes, hot rocks above 100 degrees Celcius can be found just a few miles below the surface These fields of hot rock often heat up the water in the surrounding aquifers Water heated from geothermal sources is what naturally causes geysers and hot springs It is this heated water that can be used as a heating and energy source
Types of Geothermal Fields There are three common types of geothermal fields: Hot water fields, wet steam fields, and dry steam fields. The types of fields greatly determins the type of power plant that can be built around the geothermal plant
Hot Water Fields Hot water fields are geothermal aquifers that contain reservoirs of water between 60 to 100 degrees Celcius. This type of geothermal field is the most common Hot water fields are usually used for space heating and agricultural applications, but can’t be used for much else due to their relatively low temperatures Hot water fields can also be utilized for bianary power plants, which use the hot water to evaporate a substance with a lower boiling point, which in turns spins a turbine to produce electricy
Wet Steam Fields Wet steam fields contain pressurized water that is above boiling point (100 degrees Celcius), so when the water is pumped to the surface it becomes steam. The steam from these aquifers can then be used to spin turbines and produce electricity This kind of geothermal fields is the most used for commercial applications
Dry Steam Fields Dry steam fields are very similar to wet steam fields, except the water in the geothermal reservoir is superheated, reaching temperatures of up to The superheated water similarly turns to steam upon surfacing, which again is used to spin turbines. After going through this process, however, there is still a significant amount of heat left in the water, allowing for further cycles and energy uses Dry steam fields are relatively uncommon mostly because it is rare to find such heated geothermal activity close to the earths surface
Geothermal Power Plants Power plants can be built near geothermal fields to harness their heat and convert it to electricity. The power plants must first drill two wells into the geothermal aquifers, one to pump the water to the surface and one for reinjection of the water once it has been used. This way, the water can be replenished to be reheated and used again. The power plants then use the steam from the pumped water to spin a turbine that generates electricity. From there it is cooled back into water and is pumped back down the well If the water from a geothermal field is not hot enough to turn to steam, then the hot water is used to vaporize a working fluid with a lower boiling point than water. That fluid then turns the turbine to generate electricity instead
Geothermal Heating Hot water from geothermal sources can also be used for purposes other than electricity generation. The water from a well can be piped directly into a town or city to be used for heating, or the water can be pumped for certain agricultural purposes, like pasteurizing milk This type of heating is not to be confused with a type of household heating and cooling system properly called geoexchange. However, it is often incorrectly dubbed a “geothermal heat pump,” which can cause confusion about it being a geothermal source of energy. In theory, this kind of heat is not geothermal at all, since it uses a combination of the ground’s low relative heat and indirect solar energy, not the Earth’s geothermal energy.
Non-renewable You may be surprised to learn that geothermal energy is non-renewable. This is because during the electrical generation process, a small amount of steam is lost to evaporation. Slowly, the aquifer deplenishes and the plant is no longer able to pump up water. However, a normal geothermal plant can function for a few hundred years. One way to make geothermal energy renewable is a process called hydro fracturing. In this process, pressurized water is pumped into a layer of heated rock, which cracks the rock. Sand or small beads are then used to fill the crack, but now that part of the rock layer is permeable. Now, an infinite amount water can be pumped into the rock layer to be heated and used for geothermal energy applications
Pros and Cons Pros Cons Geothermal drilling technology is very well developed and tested because of investment in similar petroleum drilling technologies. Also, geothermal heat is an infinite source and will never diminish until thousands of centuries have passed. Once the wells are drilled and the power plant is built, the electricity production process costs very little to maintain. Geothermal emits no harmful gases or wastes into the surrounding environments The cost for drilling wells is very expensive and requires careful planning to determine an effective place to drill Geothermal plants can emit some gases, like hydrogen sulfide, sulfur dioxide, and ammonia that can be somewhat irritating Many people complain that geothermal power plants are an eye-sore since they are often built next to natural parks with geysers and hot springs A large amount of cooling water may be needed, depending on the type of plant
Where it is Used Geothermal power plants can only be built in areas with volcanic activity because of their heat’s proximity to the surface So, geothermal applications are commonly used in the western United States, the Philippines, Mexico, Indonesia, Italy, Japan, and Iceland
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