Fundamentals of Geothermal Energy

Geothermal energy is the heat from the Earth. It’s clean and sustainable. Resources of geothermal energy range from the shallow ground to hot water and hot rock found a few miles beneath the Earth’s surface, and down even deeper to the extremely high temperatures of molten rock called magma. Almost everywhere, the shallow ground or upper

Geothermal energy is the heat from the Earth. It’s clean and sustainable. Resources of geothermal energy range from the shallow ground to hot water and hot rock found a few miles beneath the Earth’s surface, and down even deeper to the extremely high temperatures of molten rock called magma.

Almost everywhere, the shallow ground or upper 3 meters of the Earth’s surface maintains a nearly constant temperature between 10° and 16°C. Geothermal heat pumps can tap into this resource to heat and cool buildings. A geothermal heat pump system consists of a heat pump, an air delivery system (ductwork), and a heat exchanger-a system of pipes buried in the shallow ground near the building. In the winter, the heat pump removes heat from the heat exchanger and pumps it into the indoor air delivery system. In the summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger. The heat removed from the indoor air during
the summer can also be used to provide a free source of hot water.

Geothermal energy in this country is used in practice in health centers and spas with thermal springs, and some
countries like Island, use it for district heating of entire cities. In our country there is a big number of thermal springs that are not used in a rational way, and preliminary studies have shown that a reserve of hot water at
lower depths are in the wider area of northern Bosnia.

Geothermal resources and potential of Bosnia and Herzegovina for space heating was estimated at about 33 MWth. The temperature at locations in the city of Bosanski Samac (85oC), Kakanj (54oC) and Sarajevo (58oC) is too low to start production of electricity and therefore the main reason why the reserves are taken into consideration when it comes to exploiting heat.

Many technologies have been developed to take advantage of geothermal energy – the heat from the earth.

Geothermal Electricity Production

Most power plants need steam to generate electricity. The steam rotates a turbine that activates a generator, which
produces electricity. Many power plants still use fossil fuels to boil water for steam. Geothermal power plants, however, use steam produced from reservoirs of hot water found a couple of miles or more below the Earth’s surface. There are three types of geothermal power plants: dry steam, flash steam, and binary cycle.

Dry steam power plants draw from underground resources of steam. The steam is piped directly from underground wells to the power plant, where it is directed into a turbine/generator unit.

Flash steam power plants are the most common. They use geothermal reservoirs of water with temperatures greater than 182°C. This very hot water flows up through wells in the ground under its own pressure. As it flows upward, the pressure decreases and some of the hot water boils into steam. The steam is then separated from the water and used to power a turbine/generator. Any leftover water and condensed steam are injected back into the reservoir, making this a sustainable resource.

Binary cycle power plants operate on water at lower temperatures of about 107°-182°C. These plants use the heat from the hot water to boil a working fluid, usually an organic compound with a low boiling point. The working fluid is vaporized in a heat exchanger and used to turn a turbine. The water is then injected back into the ground to
be reheated. The water and the working fluid are kept separated during the whole process, so there are little or no air emissions.

Small-scale geothermal power plants (under 5 megawatts) have the potential for widespread application in rural areas, possibly even as distributed energy resources. Distributed energy resources refer to a variety of small, modular power-generating technologies that can be combined to improve the operation of the electricity delivery system.

Geothermal Direct Use

When a person takes a hot bath, the heat from the water will usually warm up the entire bathroom. Geothermal reservoirs of hot water, which are found a couple of miles or more beneath the Earth’s surface, can also be used to provide heat directly. This is called the direct use of geothermal energy.

Geothermal direct use dates back thousands of years, when people began using hot springs for bathing, cooking food, and loosening feathers and skin from game. Today, hot springs are still used as spas. But there are now more sophisticated ways of using this geothermal resource.

In modern direct-use systems, a well is drilled into a geothermal reservoir to provide a steady stream of hot water.
The water is brought up through the well, and a mechanical system – piping, a heat exchanger, and controls – delivers the heat directly for its intended use. A disposal system then either injects the cooled water underground or disposes
of it on the surface.

Geothermal hot water can be used for many applications that require heat. Its current uses include heating buildings
(either individually or whole towns), raising plants in greenhouses, drying crops, heating water at fish farms, and several industrial processes, such as pasteurizing milk. With some applications, researchers are exploring ways to
effectively use the geothermal fluid for generating electricity as well.

Renewable Energy Projects in Bosnia and Herzegovina

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