Greenhouses, swimming pools, recreational centers, heating and power supply systems of buildings – this just a short list of places where tamed geothermal energy works for the benefit of people. Its source lies literally under your feet: already at a depth of two or three kilometers below the surface of the earth the temperature reaches one hundred degrees Celsius, with each new kilometer increasing by another twenty degrees. Considering the interest of modern civilization towards natural hydrocarbons, geothermal energy is usually considered to be an alternative source of energy. It is the way of the future.
The reserves of natural hydrocarbons on the planet are not infinite and, moreover, are distributed very unevenly. In addition, the impact of fuel energy on the ecosystem of individual countries and the planet as a whole every year causes a growing alarm among ecologists. The energy of the earth’s interior, along with the energy of wind, water and sun, is regarded by scientific communities as a practically endless resource of renewable energy.
The distinction is made when it comes to Earth thermoenergies. Geothermal energy can be divided into petrothermal and hydrothermal. In the first case, its source is the underground rocks, in the second – the water that is under the ground.
Typically, the extraction of petrothermal energy follows these steps. In a relatively shallow, up to a kilometer, well, a heat exchanger is installed, operating on a liquid with a low boiling point – for example, freon. This coolant circulates in a closed loop. First, heated, he climbs up the concentric pipe – and then, giving up the heat, cooled, falls down. And so indefinitely – or, at least, for a very long time. Specialists in the field of petrothermal energy allocate for a continuous operation of such systems a period of time from 30 to 100 years, after which the underground elements need repair or replacement. The deeper the well, the more efficient the system. At a depth of one hundred kilometers below the surface of the earth, the temperature reaches already one and a half thousand degrees. However, such wells have not yet been drilled for any purpose, limited to their maximum depth in a few kilometers.
With hydrothermal energy – it’s even easier: no coolant is needed here. Underground waters rise to the surface with the help of a pipe system, and then, after giving off thermal energy, they return back. In seismically active zones, hot water itself rises to the surface through cracks in the earth’s crust – all that is left for people is to harness this energy. Such cases are typical, for example, for Iceland, where the energy of hot springs heats the houses and even the sidewalks – and numerous geysers in the vicinity of the Krafla volcano pass steam to one of the local geothermal thermal power plants.
However, the subdivision of subsoil energy into petrothermal and hydrothermal is somewhat simplified; in fact, the classification of geothermal sources is somewhat more complicated.
Classification of geothermal sources by the International Energy Agency:
1. Deposits of geothermal dry steam. Rarely found, but most easily developed. This energy is used by 50% of operating Geo Heat Stations.
2. Sources of wet steam (a mixture of hot water and steam). There are more often. The main problem in the development is corrosion of Geo Heat Station equipment and environmental fault tolerance due to the need to remove saline condensate.
3. Deposits of geothermal water (hot water or steam + water). Underground reservoirs formed as a result of the filling of voids with atmospheric precipitation heated by the proximity of magma.
4. Dry hot rock, reheated by magma. Depth of occurrence – from 2 kilometers and more. These reserves are the largest.
5. Magma itself – molten rocks, heated to 1300°C.
However, Iceland is a country where the use of energy of the Earth is, literally, on the surface. In general, the number of countries using petrothermal or hydrothermal energy in the world is steadily approaching eight dozen. In some of them – the United States, Japan, Kenya, Russia and others – geothermal power plants operate full time.
In general, obtaining the subsurface energy is not a cheap thing, especially at the stage of constructing the power system. This limits the use of such systems for the private sector, where traditional gas heating is much cheaper. At the same time the subsequent operation is able to recoup even the most expensive construction of this type at the expense of virtually free heat, water and electricity. Of the other advantages of geothermal power is its independence from climatic, weather conditions and the seasons – as well as its relatively high ecological compatibility: it is not fraught with any greenhouse effect. At the same time, there is a drawback: hydrothermal waters in some places of the planet can contain hydrogen sulphide, radon and other non-harmful impurities, which limits their use as a source of water supply (but not heat).
But this is rather an exception: in most countries, geothermal waters are quite safe and are used in the agro-industrial sector, industry, health care and resorts – and, of course, in housing and communal services. Among such countries are Israel, the Philippines, Greece, Kenya, Russia, Mexico, Guatemala, Indonesia, Costa Rica, Turkey and New Zealand. As for agriculture, here underground water is most often used to maintain constant temperature and humidity in greenhouses, for watering fields and heating the soil.
Geothermal power plants work differently, depending on the conditions of the terrain in which they are located – or, more precisely, on the characteristics of the energy source of the subsoil that they use. For example, in Iceland steam goes through pipes to turbines connected to electric generators. In other conditions, steam must first be cleaned of gases. In yet other cases- not water and steam are used, but a liquid coolant with a low boiling point, as already mentioned above. There are two cases of penetration at a depth of just over two kilometers directly into a layer of molten magma – in Iceland and Hawaii. And, although its energy for the operation of geothermal power plants has not yet been used, the potential of this resource is huge. Magma can meet the needs of mankind for energy for many thousands of years.
More than sixty countries of the world use energy of underground on an industrial scale; in seventy countries, a study of its deposits is under way. The engine of innovation in the field of geothermal energy in the world is the United States – even though in the country itself the need for energy due to this resource is covered by only one percent. The largest geothermal power plant in America, the “Geysers” is located in California; there are other similar facilities operating in the states of Nevada, Utah, Hawaii, Oregon, Idaho, New Mexico, Alaska and Wyoming. Among the companies offering innovative solutions for providing energy to the bowels of cities and townships – MuoviTech, Geodynamics Ltd, Vaillant, Viessmann, Nibe and others – traditionally many companies are from the USA.
The world’s largest geothermal power plant is in Kenya; Its commissioning took place quite recently – in 2014. The second largest power on the planet is the Icelandic Hellisheydi, operating on a warm source in the vicinity of the Hengidl volcano. In general, in Iceland, geothermal sources cover the country’s need for energy by almost a third. In the Philippines – a little less: here this figure is 27 percent.
As for Russia, the Far East (including Kamchatka and the Kurile Islands) and the North Caucasus are the most promising regions for the development of geothermal energy in our country. If in the European part of Russia thermal waters lie at a depth of more than two kilometers, allowing their energy to be used only point-by-point, for the heat supply of individual objects (a group of cottages, a school, a high-rise building), then in Krasnodar or Stavropol Territory the development of this resource can be conducted almost anywhere , using groundwater energy at a temperature of 70 to 126 degrees Celsius. Even more promising region of the south of the country in this sense is Dagestan, where almost a third of the republic’s housing stock is supplied with water and heat from local geothermal sources. Moreover, according to experts, extraction and use of subsoil energy in this region can be increased more than twice. The geothermal energy potential in other North Caucasian republics is also great.
Although the explosion of interest in alternative energy sources around the world occurred at the beginning of this century, for Russia, geothermal energy in particular is not something fundamentally new. The first geo-power plant in the country was built over half a century ago – in 1966 in Kamchatka, at the Pauzhetskoye field to supply electricity to local villages and fish processing enterprises. In particular, the Ozernovsky fish-processing plant was able to maintain profitability in difficult economic conditions thanks to the use of energy received by GeoTES from local hot springs.
As for central Russia, here thermal waters lie at a depth of more than two kilometers, allowing their energy to be used only point-by-point, for the heat supply of individual objects – a cottage, a school or even a high-rise building. In Skolkovo and on the basis of regional sites that implement innovations (for example, in Mordovia), projects are being created for energy-efficient “smart” houses, whose heat supply is entirely provided by geothermal energy sources. However, the creation of autonomous geothermal circulation systems with a capacity of 0.1-0.4 kilowatts for the heat and power supply of separately standing objects is a topic of special discussion, which we will not touch today. But be sure to consider this issue in one of the future issues of our magazine.
Experts believe that the potential of geothermal sources in Russia is several times greater than the volume of natural hydrocarbon reserves. One proven hydrothermal resource in Russia with a water temperature of 40 to 200 degrees Celsius with a depth of up to 3,500 meters is enough to ensure the production of 14 million cubic meters of hot water daily. However, the potential is one, and its realization is something else. Only in Kamchatka, the most “geothermal” region of the country, whose subsoil is capable of providing power to a power plant with a capacity of 250- 350 kilowatts, the available resource is used only by 25 percent of the possible.
A similar situation is in the Kuril Islands, whose geothermal resources allow the operation of power plants up to 230 megawatts, capable of covering all local needs for electricity, heat and hot water. On the island of Kunashir operates a geothermal power plant with a capacity of 2.6 megawatts. The energy it produces is used for the heat and power supply of Yuzhno-Kurilsk. In plans – construction on the island of several other similar stations, the total capacity of up to 17 megawatts. A significant amount of petrothermal and hydrothermal resources was also discovered on the islands of Iturup and Paramushir.
From other regions of the country, besides the South and the Far East, it is necessary to note the most western of all subjects of the federation – the Kaliningrad region. It has explored a large geothermal deposit with a temperature of 105-120 degrees Celsius, which makes it profitable to build a 4 megawatt power plant capable of providing electricity and heat to the city of Svetly.
In all, about fifty geothermal deposits have been explored in Russia. And, if the use of other alternative energy sources in our country is often limited by geographical and natural factors (solar energy – the fact that most of the territory lies in temperate and extreme latitudes, tidal energy – freezing seas and oceans, etc.), then the use of subsoil energy – both hydrothermal and petrothermal – is in this sense the most promising direction of development.