Machines Theory

Understanding geothermal energy

Among the renewable energy source available today, geothermal energy is one of the most common ones. It is the heat derived within the sub-surface of the earth and it is carried to the earth’s surface by water and/or steam. Geothermal energy is widely used for heating and cooling purposes or be harnessed to produce clean electricity. Today you’ll get to know the definition, applications, diagram, history, working, advantages, and disadvantages of geothermal energy. You’ll also get to know how geothermal energy is produced, and how it works.

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What is geothermal energy?

Geothermal energy is thermal energy generated and stored in the earth. The word ‘geothermal’ has Greek roots with γη (geo), meaning earth, and θερμος (thermos), meaning hot. It is renewable energy derived within the sub-surface of the earth, transport with water and/or steam to the earth’s surface. Thermal energy is the energy that determines the temperature of matter. Thus, it is known as thermal energy.

The geothermal energy of the earth’s crust originates from the original formation of the planet and from radioactive decay of materials and continual heat loss from the earth’s formation. Finally, geothermal energy is a form of energy conversion in which heat energy from within the earth is obtained and harnessed for cooking, bathing, space heating, electrical power generation, and many more uses.

In a brief history of geothermal energy, it has been proved that native Americans used geothermal energy for cooking as early as 10,000 years ago. In ancient times, baths heated by hot springs were used by the Greeks and Romans. And as for space heating, the Roman city of Pompeii during the 1st century CE, uses geothermal energy. it was initially limited to sites where hot water and steam were accessible.

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Applications of geothermal energy

The use of geothermal energy is common in over 20 countries. The United States is recorded as the largest producer of geothermal energy in the world. They have hosted the largest geothermal field known as The Geysers in California, the field is spread over 117 square kilometers and formed over 22 power plants, with an installed capacity of over 1.5GW.

Iceland also makes good use of geothermal energy since 1907, describing itself as a ‘pioneer’ of geothermal power. Over 25% of energy is produced from five geothermal power plants. They were successful due to the 600 hot springs and 200 volcanoes in the country. The applications of geothermal energy can be divided into three categories: direct use, geothermal heat pumps, and electric power generation.

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Direct uses:

The direct uses of geothermal energy involve the use of heated water from the ground without the need for any other heating source. The direct of geothermal resources is at low-temperature, which ranges from about 50 to 150 0C (122 and 302 °F). Low-temperature geothermal water and steam have been used to warm single buildings and whole districts where numerous buildings are heated from a central supply source. Also, most swimming pools, greenhouses, balneological (therapeutic) facilities at spas and aquaculture ponds have been heated with geothermal resources. Other common applications of direct uses of geothermal energy include cooking, industrial uses such as drying fruits, vegetables, and timber, milk pasteurization, and large-scale snow melting.

direct use thermal energy

Geothermal heat pumps

Geothermal heat pumps (GHPs) are used to heat buildings in the winter and cool them in the summer. They took advantage of the relatively stable moderate temperature conditions that are obtained within the first 300 meters (1000 feet) of the surface. Most GHPs temperatures are found at shallower depths such as 6 meters (about 20 feet) of the earth’s surface. Consequently, the heat can be used to warm buildings during winter, when the air temperature falls below that of the ground. Similarly, during summer, warm air is drawn from a building and circulated underground, where it loses much of its heat and is returned.

geothermal heat pump

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Electrical power generation

Geothermal energy is used to generate electricity based on the temperature and the fluid (steam) flow. Electricity is produced in three ways in geothermal power plants. These three different designs control the behavior which is used to drive electrical generators. The excess water vapor produces at the end of each process is condensed and returned to the ground, where it is reheated for later use. This is why geothermal power is considered a form of renewable energy.

see image below

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How geothermal energy works

How geothermal energy works is less complex and can be easily understood. First of all, let me explain how geothermal energy is produced. Well of up to a mile deep or more are dig into underground reservoirs so that geothermal resources can be obtained. These resources can be exploited from naturally occurring heat, rock, and water permeability. Also, enhanced geothermal systems, which enhance or create geothermal resources through the hydraulic stimulation process. These geothermal resources are further used to drive turbines linked to electricity generators.

Watch the video below to learn how geothermal energy is produced:

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The working of geothermal energy can differ depending on its end applications. I earlier mentioned the three basic use of geothermal energy. here I will be explaining how geothermal energy is used for electric power generation. Geothermal power plants come in three different designs; dry steam, flash, and binary.

Dry steam:

The dry steam design takes steam directly from fractures in the ground to drive a turbine. The heated water vapor is funneled directly into a turbine that drives an electrical generator.

dry steam geothermal power plant
Dry steam power plant generation.

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Flash plants:

Flash plant pulls high-pressure hot water from underground and mixes it with cooler low-pressure water. This, in turn, creates steam that is used to drive a turbine. Pressurized high-temperature water is drawn from beneath the surface into containers at the surface known as flash tanks. This is where the sudden decrease in pressure causes the liquid water to flash or vaporize into steam. The flash is then used to power the turbine-generator set. Finally,

flash steam power plant
Flash steam power plant generation.

Binary-cycle:

The binary-cycle power plants employ stem driven off a secondary working fluid such as ammonia and hydrocarbon contained within a closed loop of pipes to power the turbine-generator set. In this process, geothermally heated water is drawn up through a different set of pipes, and much of the energy stored in the heated water is transferred to the working fluid through a heat exchanger. The working fluid then vaporizes and passes through the turbine in order to rotate it. It then recondensed and piped back to the heat exchanger.

Binary cycle power plant generation.
Binary cycle power plant generation.

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Advantages and disadvantages of geothermal energy

Pros:

Below are the advantages of geothermal energy in its various applications.

  • Environmentally friendly than conventional fuel source such as fossil fuels.
  • Geothermal energy is renewable, they can last decades.
  • Geothermal energy is widely used.
  • It is sustainable, stable and a reliable source of energy.
  • The energy can be used for heating and cooling in direct usage.
  • No fuel is required.
  • The energy generation process has been improved by new technologies, making it a rapid evolution.
  • Its power output is easy to predict.

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Cons:

Despite the good pros of geothermal energy, some limitations still occur. Below are the cons of geothermal energy in its various applications.

  • Location is restricted, that is, geothermal plants must be built in places where energy is accessible.
  • Environmental side effects due to the digging as some gases stored under the earth are released into the atmosphere.
  • Geothermal energy can trigger earthquakes due to the alteration in the earth’s structure as a result of digging.
  • High manufacturing cost of geothermal plants.
  • High sustainability of geothermal energy fluid is required to be pumped back into the underground reservoirs faster.

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Conclusion

Geothermal energy is renewable energy derived within the sub-surface of the earth, transport with water and/or steam to the earth’s surface. Thermal energy is the energy that determines the temperature of matter. Thus, geothermal energy is known as thermal energy. The applications of geothermal energy can be divided into three categories: direct use, geothermal heat pumps, and electric power generation. That is all for this article, where the definition, application, diagram, history, working, advantages and disadvantages of geothermal energy. I also examined how geothermal energy is produced, and how it works.

I hope you enjoyed the reading, if so, kindly share with other students. Thanks for reading, see you next time!

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