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How Geothermal Energy Works

Updated on March 21, 2011

 

Geothermal energy is energy generated by geologic sources of heat and can be considered a form of renewable energy, when measured in the short term. It is based on the production of natural heat of the earth (geothermal) fed by the thermal energy released in the processes of nuclear decay of radioactive elements like uranium, thorium and potassium, contained naturally in the earth.

 

The first use of geothermal energy for electricity generation was July 4, 1904 in Italy thanks to the Prince Piero Ginori Conti, who experienced the first geothermal generator Larderello in Tuscany.

 

Geothermal energy is now less than 1% of global energy. However, a study by the Massachusetts Institute of Technology says that the geothermal energy potential contained on our planet is around 13,000 ZJ (zettajoule, 10 ² ¹ joule) and that with current technology would be able to use "only" 2000 ZJ. However, as the world's energy consumption amounted to a total of 0.5 ZJ year, with the only geothermal, according to the MIT study, it could meet the needs of planetary energies with one clean energy for the next 4000 years and then making useless to any other non-renewable source currently used.

 

Principle

Geothermal energy is a form of usable energy that comes from the heat present in the deeper layers of the earth's crust. Penetrate deep into the earth's surface, the temperature gradually becomes higher, increasing by an average of about 30 ° C per km in the crust (0.3 ° C / km and 0.8 ° C / km respectively in mantle and core). The deposits of this energy, however, are dispersed and depth so high as to prevent exploitation. To extract and use the heat trapped in the Earth, it is necessary to identify the areas with positive thermal anomaly where the earth's heat is concentrated: the geothermal reservoir or tank. To obtain an optimal heating of houses and greenhouses is put in place the action of low temperature, however, to obtain electricity use is made of high temperature fluids.

There are several geothermal systems, but currently are only exploited on an industrial scale hydrothermal systems, consisting of permeable formations where rainwater infiltrates and rivers and is heated by layers of rocks at high temperature. Temperatures range from 50-60 ° C reached up to several hundred degrees. The use of this energy has advantages such as inexhaustible in the short term, if exploited in a rational and less pollution of the environment, some pollution is not ruled out the possible release of toxic elements in the area, such as sulfur , mercury and arsenic found in geothermal fluids, so the geothermal areas are subjected to annual environmental audits.

 

Looking only to the production of thermal energy, is the low-enthalpy geothermal system that using the natural heat of the soil with the help of a heat pump can produce heat for domestic hot water and space heating of buildings.

In some particular areas is likely to present conditions in which the Earth's temperature is higher than the average, a phenomenon caused by volcanic or tectonic phenomena. In these areas "hot" energy can be easily recovered by geotermia.La geothermal energy is to convey the vapors from the underground water sources used for the routing to turbine power generation and reusing the steam for district heating , crops in greenhouses and spas.

To power the production of water vapor is often used for placing cold water in depth, a useful technique to maintain a constant flow of steam. In this way you can make the turbines work at full capacity and releasing heat continuità.La geothermal is still a marginal source of energy to be used only in limited territorial contexts. It is in any case a potential energy to be exploited where possible, exploiting the potential of geothermal heating.

In this sense seem to be very promising developments for energy geomagmatica, which has a very wide geographical distribution because of the absence of water use but only calore.The natural radioactivity of the earth is the cause of geothermal energy. It is estimated that the total flow of heat to the earth's surface is 16-TW, then since the earth has a mean radius of 6371 km, the average power produced by geothermal power is 32 mW / m². For comparison, the average solar radiation, the European latitudes, about 200 W / m². The power is significantly greater near the limits of tectonic fractures where the crust is not thick. In addition, the circulation of deep water can further increase the thermal power per unit area.

 

World Development

 

The geothermal energy is the luck of Iceland, where 85% of the homes are heated by this energy source. The largest island in the North Atlantic based his whole life on the natural balance between the presence of hot water deep beneath the outer atmosphere and zero.Il the world's largest geothermal power complex is located in California at The Geysers (the plant has a potential of 1400 MW, enough to meet the energy demands of the metropolitan area of San Francisco). In Africa, Kenya and Ethiopia have built plants to geothermal energy. In Ethiopia, Iceland has calculated that geothermal energy is present at least 1000 MW. It is estimated that twenty countries around the world have geothermal development projects. Even Google has invested in geothermal third generation, based on drilling depth to reach the hot spots of the crust even in areas not naturally springs.

 

The low energy geothermal

 

The low energy geothermal uses the underground to store heat. In winter the heat is transferred to the surface, back in the summer the excess heat in buildings, is given to the ground. This is made possible by the heat pumps, engines that we all know the most common form represented by the refrigerator. These systems do not require special environmental conditions, nor in fact do not exploit the natural springs of hot water, or areas where the soil has a higher than average temperatures due to a special closeness with his cloak. What this technology has the advantage that the soil has a constant temperature throughout the year. Normally, already one meter deep, you manage to have about 10-15 ° C.

 

At this point you use the heat pump that uses the heat difference between the ground and the outside to absorb heat from the ground and make it available for human uses. The more this difference is higher the better the performance. The heat pump requires electricity for operation, in average conditions for each kW consumed you get 3 kW electric heat. To make the system more environmentally compatible and energy self-sufficient, can be combined with a photovoltaic system that will produce the energy needed to power the heat pump. The same system can be used to cool the buildings, running the heat pump on the contrary, then by absorbing heat from the surface and transferring it to the ground. The alternation of summer / winter can not cool down significantly clod of soil in which the probes are located.

 

One of the first plants built in Italy, which supplements the geothermal with photovoltaics and solar thermal has been realized in Porretta Terme, a small town in the province of Bologna. As a result of European funding the Hundred CISA inaugurated in March 2008, the facility that feeds the local Civic Centre - Seniors Centre owned by the town.

 

Geothermal probes

 

To transfer the heat from the ground are used for geothermal: U-shaped tubes made of materials with high thermal transmittance which handle a liquid that absorbs heat and carries it to the surface or underground. The probes can be of two types:

 

·         vertical

·         horizontal

 

In the first case the probe descends into the ground by going to higher temperatures and requiring special equipment for the drill ground in the second case requires a sufficiently flat ground where the pipes are laid as a result of a simple excavation to a depth not high . In the second case the probes can also be placed on the bottom of a lake or natural advantage in this case, the heat of the water.

 

The geothermal power plants

 

The flow of steam from the ground that produces a force to move a turbine, the mechanical energy of the turbine is then converted into electricity via an alternator system. Geothermal systems can be vapor-dominated, when the high temperature causes the formation of accumulations of vapor or water-dominated, if the water remains liquid. In the first case of geothermal energy can be used to generate electricity, sending the steam through the steam ducts, to a turbine connected to a generator. If the fluid does not reach a sufficiently high temperature, hot water can be used to produce heat for district heating in the example.

 

Benefits

Geothermal energy can be drawn from the natural forces a large amount of renewable and clean energy. These plants also do not pose a threat to the environment, as it was deemed clean. Another advantage is the possible recycling of waste by encouraging savings. The drilling is more expensive, in 2005, geothermal energy cost between 50 and 150 euro per MWh, but it seems that this cost has dropped to 50-100 euro per MWh in 2010 and is projected to fall to 40-80 € per MWh in 2020.

 

Disadvantages

The geothermal source receives two criticisms in particular:

 

·         From geothermal power plants with steam coming out even the typical unpleasant odor of rotten eggs caused by hydrogen sulphide thermal areas. A problem generally tolerated in the case of spas, but particularly against the population living near a geothermal power plant. The problem is solved by the installation of any abatement equipment.

 

·         The external impact of geothermal plants can make any landscape problem. The central presents, in fact, like a tangle of pipes anti-aesthetic. An image that is not, however, from that of many other industrial sites or factories. The problem landscape can be easily solved by combining the functional approach of engineering with an architecture that respects the landscape and the common sense of aesthetics.

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