GEOTHERMAL POWER EXPLAINED |
TYPES OF INSTALLATION |
As you dig deeper into the ground the temperature increases, this heat is what we can use to make electricity. Scientists has calculated the temperature of the core of the earth to be around 6.000 °C (10.800 °F) which is as hot as the surface of the sun.
Some of this heat is being transferred to the crust of the earth, and away from tectonic plate boundaries the geothermal gradient is increasing temperature about 25 °C per km of depth (1 °F per 70 feet of depth) near the surface in most of the world. |
Because of the different reservoir characteristics, the surface installations required to convert the heat into energy will vary. Some types of installations are:
|
Heat from Earth's interior can be used as an energy source, known as geothermal energy. The geothermal gradient has been used for space heating and bathing since ancient Roman times, and more recently for generating electricity.
As the human population continues to grow, so does energy use and the correlating environmental impacts that are consistent with global primary sources of energy. This has caused a growing interest in finding sources of energy that are renewable and have reduced greenhouse gas emissions. In areas of high geothermal energy density, current technology allows for the generation of electrical power because of the corresponding high temperatures. Generating electrical power from geothermal resources requires no fuel while providing true baseload energy at a reliability rate that constantly exceeds 90%. On a worldwide scale, the heat stored in Earth's interior provides an energy that is still seen as an exotic source. About 12.8 GW of geothermal electric capacity is installed around the world as of 2015, spread across 24 countries. Based on current data the global geothermal industry is expected to reach between 14.5 GW and 17.6 GW by 2020. Communities and governments around the world have only tapped 6.5% of the total global potential for geothermal power based on current geologic knowledge and technology. The World Bank estimates as many as 40 countries could meet a large proportion of their electricity demand through geothermal power. In order to extract geothermal energy, it is necessary to efficiently transfer heat from a geothermal reservoir to a power plant, where electrical energy is converted from heat. A geothermal system that can be developed for beneficial uses requires heat, permeability and water. When hot water or steam is trapped in cracks under a layer of impermeable rock, it forms a geothermal reservoir. Rainwater and snowmelt continue to feed the underground thermal aquifers and the hot rocks heat up the water. Prince Piero Ginori Conti
Prince Piero Ginori Conti proved the viability of geothermal power plant technology in 1904, at the dry steam field in Larderello, Italy. The geothermal field has produced continuously since then, except for a brief period during World War II, and is still producing today. |
Flash Power Plant
In a geothermal flash power plant, high-pressure geothermal water separates into steam and water as it rises from depth and the pressure drops. The steam and liquid are separated in a surface vessel, called a steam separator. The steam is delivered to the turbine, and the turbine powers a generator. The liquid is then injected back into the reservoir to repeat the process. Dry Steam Power Plant
In a geothermal dry steam power plant, steam alone is produced directly from the geothermal reservoir and is used to run the turbines that power the generator. Because there is no water involved, the steam separator used in a flash plant is not necessary. Binary Power Plant
Binary geothermal plants have made it possible to produce electricity from geothermal resources lower than 302°F (150°C). This has expanded the industry’s geographical footprint, especially in the last decade. Binary plants typically use an Organic Rankine Cycle (ORC) system. Geothermal water is used to heat another liquid called a working fluid or motive fluid, such as isobutane or pentafluoropropane, which boils at a lower temperature than water. A heat exchanger then separates the geothermal water from the working fluid while transferring the heat energy. When the working fluid vaporizes, the force of the expanding vapor, like steam, turns the turbines that power the generators. The geothermal water is then injected back into the reservoir in a closed loop, separating it from groundwater sources and lowering emission rates further, possibly to zero. In 1981, Ormat Technologies established the technical feasibility of larger-scale commercial binary power plants at a project in Imperial Valley, California. The project was so successful that Ormat repaid its loan to the Department of Energy within a year. Flash/Binary (Combined) Power Plant
Hybrid power plants allow for the integration of numerous generating technologies. In Hawaii, the Puna flash/binary combined cycle system takes advantage of the benefits of both flash and binary geothermal technologies. Geothermal fluid is flashed to a mixture of steam and liquid in a separator. The steam is fed to a turbine as in a flash-steam generator and the separated liquid is fed to a binary cycle generator thereby achieving dual output. Enhanced Geothermal System (EGS)
An Enhanced Geothermal System (EGS) is a man-made reservoir, created where there is hot rock but insufficient or little natural permeability or fluid saturation. In an EGS, fluid is injected into the subsurface under carefully controlled conditions, which cause pre-existing fractures to re-open, creating permeability. Increased permeability allows fluid to circulate throughout the now-fractured rock from the injection well into a production well drilled to intersect the stimulated fracture system created by the injection well, and then transport heated water to the surface where electricity can be generated through a binary power plant. Additional production wells can now be drilled into the man-made reservoir to extract more heat from the large volumes of rock mass and meet power generation requirements. |