Geothermal energy is energy that can be obtained by man through the use of heat inside the Earth. The heat inside the Earth is due to several factors, including the geothermal gradient, the radiogenic heat, etc. Geothermal comes from the Greek ``geo´´(earth) and ``thermos´´(hot), literally ``heat of the Earth´´
In areas of very hot thermal waters at little depth, it is perforated by natural fractures of basal rocks or within sedimentary rocks. The hot water or the steam can flow naturally, by pumping or impulses of steam and water flows (flashing). The magma resources (fused rocks) offer geothermal energy of highest temperature, but we can not take economically advantages of it with the existing technology.
In most of the cases the operation should be done with two wells so that one gets the hot water and the other re-injected the water into the aquifer, before cooling the wealth obtained. There are many advantages with this system:
There are less probabilities of exhausting the thermal deposit. The water of the deposit is not exhausted because the total amount remains.
The possible salts or gas emissions dissolved in the water do not appear, avoiding contaminations.
Types of geothermal deposits according to the temperature of the water
The geothermal energy of high temperature exits in the active zones of the crust. This temperature is between 150 and 400ºC, produce steam in the surface and it generates electricity with a turbine.
Geothermal energy of average temperatures: is the one in which the temperature of the aquifer’s fluids are less high, normally between 70 and 150ºC. So the steam-electricity conversion is made with a smaller yield, and must be exploited by a volatile fluid.
We can use the geothermal energy of low temperatures in zones that are bigger than the other ones; for example, in all sedimentary basins.
I t is considered geothermal energy of very low temperature when the fluids are warmed up to temperatures between 20 and 50ºC. This energy is used for domestic , urban or agricultural necessities.
The lower temperature sources are very suitable for heating system.
Advantages and disadvantages
It i s a source that would avoid the energetic dependency of the outside.
The wasted productions are minimum and they caused a smaller environmental impact than the ones that are originated by petroleum, coal,…
In some cases, the emission of hydrogen sulfide, that is detected by its rotten eggs smell but you can not perceive it in large amounts and is lethal.
In some cases, emissions of CO2, with increased greenhouse effect, is less than what would be issued to obtain the same energy by combustion.
Water contamination with substances like arsenic, ammoniac, etc .
Deterioration of the landscape.
You can not transport it (as primary energy).
It is available only in certain places.
Geothermal energy uses
Use of heat
Heating and ACS.
Geothermal energy was produced for the first time in Larderello, Italy, in 1904. Since that time, the use of the geothermal energy for electricity has grown worldwide near 8,000megawatt of which EE.UU generates 2,700MW.
Types of electrical plants
Three types are used to generate power from geothermal energy :
Pla nts ``in dry steam´´usually take the stream from the fractures in the ground and it goes directly to a turbine, to move a generator. Plants ``flash´´obtains very hot water of more than 200ºC, and separats in the steam phase with separators steam/water, and it moves a turbine. In binary plants, the hot water flows through heat exchangers, by boiling an organic fluid that turns the turbine.
Douglas Firestone began with the desalination with the evaporation/desalination system with hot air in 1998, proving that the hot water can be used economically to produce desalinated water in 2001 .
In 2003, the teacher Ronald A. worked with Firestone to improve the process of geothermal energy for desalination.
In 2005 , is fitted the 5th prototype desalination ``Delta T´´that uses a forced hot air cycle, atmospheric pressure and a geothermal cycle of evaporation and condensation.
Injection and water
In many places has happened that magma deposits dried up. As a result, it stops providing geothermal water , perhaps helped by the injection of cold wastewater or in the hot aquifer recharge. That means that the reinjection recharge can cool the resource, unless you be careful with it. In at least one town, the cooling was the result of small but frequent earthquakes . This has brought the discussion if the plants ownwers are responsible of the damaged caused by an earthquake.
Although there are sites capable of providing geothermal energy for decades, others may dry and run . In a report, the Icelandic government says: should be understood that geothermal energy is not strictly renewable in the same direction as the hydraulic.
¿How do they work?
The operation of a geothermal power station is done through a very simple system: two tubes that have been introduced in the practiced perforation, maintain their ends in a closed circuit in direct contact with the heat source. On one end of the tube is injected cold water from the surface, when it comes to the bottom it is warmed up and ir rises toward the surface across another tube, that has got a turbine with an electrical generator. The cooled water is given back by the first tube to repeat the cycle again.
Disadvantages of the system
The abyss inside the earth’s crust, where is the usable heat, is not able to conduct the heat. In practice, this disadvantage prevents the continuous operation of the power station.
In a certain way a geothermal power station reproduces the natural operation of the geysers; in that case the water is introduced through the cracks of the subsurface and on having reached the heated zones of the Earth, they are taken to boil, returning to the outside by those holes that offer less resistance, offering a very showy spectacle.
Geothermal power stations in Spain
In the case of Spain, although there are suitable places to build in Almeria,there are not any geothermal power station yet. In the Canary island La Palma, many people are studying the construction of a geothermal plant which covers part of their electricity’s needs, because at the present time, the island dependency of fossil fuels is 95%.