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Geothermal Energy

The United States and other nations are both powered by geothermal energy, sometimes referred to as the heat of the Earth, which is a sustainable, natural resource. Deeper reservoir temperatures (between 200 and 700 °F) are the working range for large-scale, commercial geothermal power plants in the United States since the 1960s. Geothermal energy exploration and development is a booming global sector. 

What is geothermal energy?

Geothermal energy is a kind of renewable energy that is extracted from the core of the Earth. The sources of this energy include the heat generated during the planet’s initial formation and the radioactive decay of components. Both the Pacific Northwest Electric Power Planning and Conservation Act (NEPPCA) of 1980 and the National Energy Policy Act (NEPA) of 1992 recognized it as a renewable resource. 

The earth’s core and surface have different temperatures, which causes thermal energy to flow continuously from the planet’s interior to its surface. A portion of the Earth’s interior rock melts at temperatures exceeding 4000°C to generate hot, molten rocks known as magma. Since the mantle is lighter than the underlying rock, it also exhibits plastic behavior in response to these temperatures, causing some of it to convect upward.  

From modest depths to many miles below the Earth’s surface, thermal energy is present in the rocks and fluids. 

Figure 1: Earth’s Temperatures

Indigenous societies from all over the globe have long utilized geothermal energy for heating and other reasons. For example, the Māori’s and the Native Americans have long used hot spring water for therapeutic and culinary purposes. While the inhabitants of Pompeii, who were forced to live too near Mount Vesuvius, heated their homes with hot water that they extracted from the ground.  

What is a baseload power source? What is a dispatchable power source?

Baseload power is the minimum quantity the grid must always receive. Not ideal, but power plants must keep up with daily energy demand patterns. Coal-fired and peaking power plants offer baseload energy, which is only sometimes enough due to regular energy consumption fluctuations. The system needs peaking power to meet electrical demands.  

While a dispatchable energy source, such as a power plant, may be switched on or off or adjusted as required. Most conventional energy sources, including coal and nuclear power, can supply the population’s electrical demand. Wind and solar energy are unpredictable, non-dispatchable, and can only create leverage during their main energy flow. 

How does a conventional geothermal power plant work?

Most power plants utilize heat to turn water into steam, which drives a turbine to generate electricity. Not an exception, geothermal energy plants produce heat by using hot water that is located deep inside the Earth rather than burning coal or oil. These deep hydrothermal reservoirs naturally generate the steam that reaches the Earth’s surface via hot springs, geysers, and even volcanoes. Geothermal resources and infrastructure are often located close to the edges of tectonic plates, where fractures enable stored deposits to rise to the surface. 

Dixie Valley, NV, Flash Plant


The steam turns a turbine, which starts a generator and generates energy. Below are the three kinds of geothermal power plants: binary cycle, flash steam, and dry steam. 



Dry Steam 

Power plants that use dry steam get their steam from subsurface reservoirs. Directly from subterranean wells, steam is pumped to the power plant and routed into a turbine/generator unit. In the United States, there are just two known subsurface sources of steam: 

Yellowstone National Park in Wyoming is home to the well-known geyser known as Old Faithful, as well as the geysers in northern California. 

The Geysers is home to the only dry steam plants in the nation since Yellowstone is protected from development. 

Flash Steam 

The most prevalent usage of geothermal reservoirs of water with temperatures over 360°F (182°C) is in flash steam power plants. Under its own pressure, this very hot water rises via underground wells. A portion of the hot water boils into steam as it rises due to the pressure drop. Following its separation from the water, the steam fuels a turbine/generator. As condensed steam and any residual water are pumped back into the reservoir, the resource is renewable. 

Binary Steam 

Binary plants use geothermal water to heat a different liquid that boils at a lower temperature than water, such as pentafluoropropane or isobutane. In 1981, Ormat Technologies conducted a demonstration of the viability of binary geothermal power plants in Imperial Valley, California. The project’s success allowed Ormat to pay back its DOE financing in less than a year. The presence of binary geothermal plants, which can produce energy from sources with temperatures below 150°C, has increased in the U.S. sector during the last 10 years. 



How do geothermal heat pumps work?

The most cost-effective, ecologically friendly, and energy-efficient technologies for heating and cooling buildings, according to the U.S. Environmental Protection Agency (EPA), are geothermal heat pumps. Geothermal heat pumps may be used in any structure, including residences, workplaces, institutions of higher learning, and hospitals. 

A typical system includes a ground loop system, a heat exchanger, and ducting in the building. Water solution circulates through subterranean pipes throughout the winter and absorbs ground heat. A water-to-air heat pump focuses the thermal energy and turns it into air in a standard ducting system to heat the home once warm water is carried inside. The home’s excess heat is either pumped into the ground or utilized to heat domestic hot water so that it may be chilled throughout the summer. 


Figure 9: Geothermal Heat Pump Diagram


A water-to-water heat pump concentrates heat for a hydronic radiant floor heating system. The heat from the house is transferred into the ground pipes throughout the summer by the heat pump, which releases extra heat there. 

A desuperheater, which heats the water by recycling waste heat from the heat pump compressor, may be used in geothermal exchange systems. These gadgets might be used in addition to solar or traditional water heaters. Free hot water is produced in the summer when the hot water tank receives extra home heat. In the winter, underground heat may reduce water heating costs by up to 50%.

How do direct use applications work?

Heat may also be generated directly from geothermal reserves of hot water that are located many miles or more below the surface of the Earth. The direct usage of geothermal energy is what is meant by this.

Figure 10: Direct Use Geothermal Heating System Configuration


Underground hot water is used directly from geothermal resources to heat buildings, grow plants in greenhouses, dry onions and garlic, heat water for fish aquaculture, pasteurize milk, and many more purposes. To melt snow, several communities pump hot water beneath the sidewalks and roadways. Applications for district heating employ networks of hot water pipes to heat buildings across whole cities. 

Direct geothermal energy use is much less costly than utilizing conventional fuels for households and businesses. When compared to fossil fuels, savings may reach 80%. It also produces extremely little air pollution, sometimes none at all, compared to what is produced by burning fossil fuels. 


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