The Earth has its own internal energy, that is responsible for the dynamics of our planet, and volcanic activity is its most evident example, however, this energy also spreads silently and continuously towards the surface in the form of heat: this occurs in every spot of the Earth, even in those areas which do not seem to have any volcanic or geologic activity.
Deeper and deeper into the subsoil, the rock temperatures increase with a gradient of 1°C every 33 m in depth on average, even though there are areas which are particularly active, where the temperature increase is more consistent (as for example in volcanic areas): in these particular areas, the so called geothermal fields, the energy found deep in the Earth is exploited to produce electric power. However, this requires very high temperatures, so it is possible only in some fields, called high enthalpy fields (or high temperature fields). The Earth’s internal heat can be exploited also when the temperatures are not very high, not for the production of electricity but to obtain heat for domestic heating or for other industrial uses (refer to the special report on geothermal energy). If special devices such as heat pumps are connected to the process to “capture” endogenous heat, an “indirect” use of thermal energy of the Earth becomes possible, and much lower temperatures of “direct” geothermal energy can be exploited: and therefore there is the possibility of a greater diffusion of this use of geothermal energy also in areas without the particular geological conditions of the geothermal fields.
Geothermal electricity power plants can be of different types; “back pressure system” if the steam, after being exploited, is freed into the atmosphere; “condensing system”, if the utilized steam is condensed and newly injected into the subsoil, through an injection well. “Flash” power plants are installed in areas dominated by water and are equipped with separators that separate the steam sent to the turbine, from the water that is then eliminated.
Air conditioning plants
With geothermal power it is possible to supply our houses with air-conditioning. Small geothermal plants are built for small buildings, medium-sized and big buildings. A heat well is made by drilling with an adequate drill and using some coating tubes deep underground in order to prevent the land from sliding down.
A practically inexhaustible source of energy to heat our homes at a very low cost and in a clean and environment respectful manner: this is the dream of millions of families all over the world… certainly also ours! Geothermic energy seams to answer all these requests and, since the dawn of civilization, man has learnt to use the heat inside the Earth. Initially man enjoyed the pleasure of thermal baths with naturally heated water and later on, at the beginning of the 20th century, learning to use water to produce electric energy. Moreover, water was also used to warm houses of entire cities (the first district heating plant was started in Iceland in 1925). However, until a few years ago, the use of geothermal energy for domestic heating had two important limits which strongly held back its diffusion: geothermal power could be obtained in the presence of relatively high temperatures (60 – 80 °C) and only in the area of the geothermal fields; the heat used was therefore endogenous: it was not possible to transport the heat too far from its source nor was it possible to use it at a low temperature (that is to say at a “low enthalpy”). With the recent technological developments, it is now possible, through particular instruments known as heat pumps, to use the heat of the Earth even when temperatures are not particularly high (12 – 14 °C). This has brought about a new and important step forward in geothermics: with these new systems, it is in fact possible to obtain sufficient energy for a family’s everyday heating and warm water consumption, in any place of the Earth, with any geological or climatic condition. The energetic possibilities of this new technology are huge and potentially unlimited.
The Sun's contribution
The subsoil does not only receive energy from the depths of the planet. The Sun's energy warms the Earth's surface and about 47% is directly absorbed by the soil: the temperature in the first metres of the subsoil is subjected to daily and seasonal variations according to the radiation received.
How it works
Even though it is characterised by very high technology and very high performance, a domestic geothermal system is very simple. It consists of three principal elements: geothermal sensors or probes; heat pump, or thermopump; an internal heat distribution system.
A “domestic” energy: geothermics for homes
“Classic” geothermic uses heat directly from the Earth, using warm water extracted from the subsoil and then distributed to households or industrial installations. Now the use of special instruments, heat pumps, allows a much larger use of geothermic, independent from the particular conditions of a geothermal field.
What is a heat pump?
A heat pump is an instrument which allows heat exchange between a source of energy (for example the ground but also the air of the atmosphere or the water of the ground water table) and an environment with a different temperature. It works like refrigerator, and can work both ways (for heating in winter or for cooling in summer).
Different types of probes
To “capture” the heat of the subsoil, two types of probes are used, depending on how deep they are positioned.
In order to use geothermal energy, “vertical probes” are set up. These are simply a couple of U-shaped pipes with a 10 - 18 cm diameter, that are positioned in wells at variable depths, between 50 and 350 m.
Domestic geothermic installations can entirely replace a traditional combustion plant with an autonomous and not just integrative solution (as in the case of solar panels, which do not allow a complete autonomy due to the variability of the energy supplied).
An inexhaustible energy
The geothermal air-conditioning system a possibility to heat and air-condition our homes in a manner that is clean and sustainable for the environment. In fact, this system produces very low levels of CO2 and gases which are noxious for the environment.
A healthier home
The environmental benefits of this new form of geothermal energy exploitation are evident, not only on a “global” scale, but also inside homes, this system helps creating a healthier atmosphere. In fact as there are no open flames, no exhaust gases, no fumes, no fine particles are produced , and no oxygen is burnt, therefore the air inside the home will be cleaner.