Nowadays, it may seem difficult to imagine our lives without electricity or other basic comforts. However, the current situation of our planet is forcing us to look for new resources and sources of energy, as the fossil fuels we use are beginning to be endangered and threaten to run out. From EcologíaVerde we are going to talk to you about geothermal resources as a renewable energy source in this article about geothermal energy: definition, advantages and disadvantages .
What is geothermal energy – definition
Geothermal energy ( from the Greek geo, Earth, and thermos , heat; that is, “heat of the Earth”) is a type of renewable energy that, as we can deduce from its name, uses as a source the internal heat of the Earth stored under the surface. The Earth’s core is formed by a solid incandescent sphere and is composed fundamentally of an alloy of iron and nickel that radiates heat outwards. Thus, the deeper layers have higher temperatures and in them the heating of water masses can occur which, when rising in a liquid or vapor state, manifest themselves in the form of geysers or hot springs.
This heat is not transmitted in a linear manner to all points on the planet and, in addition, depends on the material it passes through. The most superficial area of the Earth’s crust, the lithosphere, transports heat by conduction (through contact between the two bodies but without the transfer of matter) and as the depth increases, the heat is transmitted by convection (produced by the transfer of the heat-carrying matter, generally a gas or liquid, to the receiving body).
Currently, geothermal energy is used for heat production, cooling and electricity generation .
Types of geothermal energy
There are 4 types of geothermal energy depending on the temperature of the water when it is expelled:
- High temperature geothermal energy , between 150 and 400º. On the earth’s surface it is converted into steam and generates electricity through a turbine.
- Medium temperature geothermal energy , between 70 and 150º, exploited by small power plants.
- Low-temperature geothermal energy , between 50 and 70º, used mainly for domestic needs such as heating and, more occasionally, in greenhouses or agriculture.
- Geothermal energy at very low temperatures , between 20 and 50º. As this is not sufficient for air conditioning, geothermal heat pumps must be used for both heating and cooling.
Within this section we can also refer to geothermal energy from hot rock deposits, approximately 5-8 kilometres deep underground (dry deposits).
Geothermal energy sources
Generally, the rate at which these deposits are exploited is usually high, so areas that would take hundreds of years to recover should not be saturated.
Geothermal deposits , sites where large concentrations of geothermal energy accumulate, can be classified into three types:
Hot water deposits
This type of deposit can be found in the form of springs or underground in aquifers. The former have been used for a long time as thermal baths by the Romans. Underground deposits have high temperatures but at low or medium depths, so that hot water or steam can flow naturally. However, if it is to be extracted for exploitation, two or an even number of wells must be made to extract the water and reintroduce it once cooled to prevent the aquifer from drying out and being lost as a thermal deposit.
Dry deposits
These deposits do not need water to produce energy, since it is actually a type of artificial production. They are located underground at a not very great depth, and are made up of dry rocks at high temperatures due to exposure to the magma inside. Cold water is injected into them, which when it comes into contact with the hot rock produces water vapour, which comes out under pressure through a second perforation also in contact with the hot bedrock.
Geysers
They may be the clearest example we can all think of, but that does not mean they are excessively abundant, with most of them found between Iceland and Yellowstone National Park (USA), which are mainly volcanic areas.
These geysers are large sources of boiling hot water capable of violently expelling columns of steam and hot water. The explanation for this phenomenon is based on the contact of the subsoil waters with rocks that remain at high temperatures inside the Earth. This causes the water to heat up and volatilize almost instantly, rising towards the surface at high speed and being expelled as if the geyser were a siphon of water and steam.
Advantages of geothermal energy
This type of energy has both advantages and disadvantages that are worth knowing. Thus, among the main advantages of geothermal energy we highlight the following:
- It is a renewable resource, provided that its extraction rate is lower than the natural recharge rate.
- It is considered a “clean” energy, as it reduces the consumption of fossil fuels and other non-renewable resources.
- It produces very little waste, which greatly reduces the environmental impact.
- The emission of greenhouse CO2 is much lower than that produced by combustion to obtain the same energy, so it hardly contributes to global warming.
- It represents savings since its costs for electricity production are low.
- It provides a vast amount of resources; it is believed that today it can provide more energy than all fossil fuels (oil, natural gas, coal and uranium) combined.
Disadvantages of geothermal energy
Furthermore, as we have mentioned before, geothermal energy also has drawbacks :
- Underdeveloped as this is an energy that is just beginning to be used. In Spain it is hardly used and the extraction methods can currently be considered somewhat ordinary.
- Leaks may occur in which hydrogen sulfide (in high doses it is lethal to humans), arsenic, ammonia or other substances are expelled that can cause contamination of the land and nearby waters.
- Geothermal plants or power stations must be installed in places where the heat from the subsoil is high.
- This energy is not transportable and must be used on-site , that is, in the same place where it is produced (local supply).
- They have an impact on the landscape, since the construction of facilities to extract heat from underground rocks and magma requires modifications to the terrain.
- Small earthquakes occur in areas close to geothermal plants due to the sudden cooling and breaking of rocks in the Earth’s crust.
- Thermal pollution.
- Noise pollution. In the initial phases when drilling wells is necessary, noise levels can reach up to 115 decibels (almost the same noise as an airplane engine), although once the well has been drilled, its normal operation produces hardly any external noise (it is between 75 and 80 decibels, the noise of a vacuum cleaner).
