Geothermal Energy Definition

  • Published on March 16th, 2016

Finding a correct geothermal energy definition on the Internet can lead to a variety of interesting information concerning this renewable energy source.

For basics, I begin with a sampling of definitions. Here is an excellent one from V. Ryan at TechnologyStudent:

“The term Geothermal originates from two Geek words ‘GEO’ and ‘THERM’. The Greek word ‘geo’ meant the earth whilst their word for ‘therm’ meant heat from the earth.

“Geothermal energy is energy derived from the heat of the earth. The earth’s centre is a distance of approximately 4000 miles and is so hot that it is molten. Temperatures are understood to be at least 5000 degrees centigrade. Heat from the centre of the earth conducts outwards and heats up the outer layers of rock called the mantle. When this type of rock melts and becomes molten it is called magma. Magma can reach just below the earths surface.

“Rain water sometimes seeps down through geological fault lines and cracks becoming super heated by the hot rocks below. Some of this super heated water rises back to the surface of the earth where it emerges as hot springs or even geysers. Sometimes the hot water becomes trapped below the surface as a geothermal reservoir.”

geyser erupting shutterstock_298742318
The Strokkur Geyser erupting at the Haukadalur geothermal area, part of the golden circle route, in Iceland.

.As a noun, the dictionary defines geothermal energy as “a form of energy obtained fromwithin the earth, originating in its core.” In short, it is energy produced by extracting the Earth’sinternal heat, which happens to be remarkably hot. To comprehend how hot this is, think about where a volcano’s lava from.

This heat happens to be extraordinarily hot at its core, most recently calculated to measure 6,000 degrees Celsius (10,832 F), a solid 1,000 C (1,832 F) hotter than previously believed when the last temperature model was run 20 years ago, NatureWorldNews has reported.

Sounds simple enough, correct? Nothing more than the simple act of redistributing this heat from Earth. As long as you have the right tools, that is, and happen to be situated in an ideal geographic location.

A renewable energy resource


Geothermal energy is a renewable resource.   One of its biggest advantages is that it is constantly available.  The constant flow of heat from the Earth ensures an inexhaustible and essentially limitless supply of energy for billions of years to come.

The National Energy Policy Act of 1992 (Sec. 1202) and the Pacific Northwest Electric Power Planning and Conservation Act of 1980 (Sec. 12H, 839a(16), page 84) both define geothermal energy as a renewable resource.

According to the Geothermal Energy Association, this heat of the Earth delivers a clean, renewable resource which provides energy in households the world. The US has been using commercial, large-scale geothermal power plants at deep resource temperatures (between 200˚F and 700˚F) since the 1960s. Geothermal energy development and production is a thriving international market.

Heat has been radiating from the center of the Earth for some 4.5 billion years.  Scientists estimate that 42 million megawatts (MW) of power flow from the Earth’s interior, primarily by conduction.

Regarding clean energy technologies, the Geothermal Resources Council (GRC), Geothermal Energy Association (GEA), and Geothermal Exchange Organization (GEO) have released guidance for U.S. states on meeting new clean energy standards from the U.S. Environmental Protection Agency (EPA).

Putting geothermal energy to use

These state-by-state guides introduce people to the benefits and uses of three major types of geothermal applications, including:

  • Power generation – Geothermal power plants use hydrothermal resources that have both water (hydro) and heat (thermal). Geothermal power plants require high-temperature (300°F to 700°F) hydrothermal resources that come from either dry steam wells or from hot water wells. People use these resources by drilling wells into the earth and then piping steam or hot water to the surface. The hot water or steam is used to operate a turbine that generates electricity. Some geothermal wells may be as deep as two miles.
  • Direct use – Ancient Roman, Chinese, and Native American cultures used hot mineral springs for bathing, cooking, and heating. Today, many hot springs are still used for bathing, and many people believe the hot, mineral-rich waters have natural healing powers. Geothermal energy is also used to heat buildings through district heating systems. Hot water near the earth’s surface can be piped directly into buildings and industries for heat. A district heating system provides heat for most of the buildings in Reykjavik, Iceland.
  • Heat pumps – According to the US Environmental Protection Agency (EPA), geothermal heat pumps are the most energy efficient, environmentally clean, and cost-effective systems used for temperature control. Geothermal heat pumps can be used for all types of buildings, including homes, office buildings, schools, and hospitals.

The GRC Geothermal Library

For anybody researching geothermal technologies, GRC’s database contains over 40,000 records and access to over 21,000 PDF files on all aspects of geothermal energy, including exploration, reservoir engineering, power plant design and operation, direct use, geothermal heat pumps, regulatory issues, energy policy, energy markets, and news briefs.

Geothermal Energy Advantages

  • Environmentally friendly – There are a few polluting aspects to harnessing geothermal energy, and the carbon footprint of a geothermal power plant is seen as minimal. An average geothermal power plant releases the equivalent of 122 kg CO2 for every megawatt-hour (MWh) of electricity it generates – one-eighth of the CO2 emissions associated with typical coal power plants.
  • A renewable resource – Geothermal reservoirs are naturally replenished. According to some scientists, the energy in our geothermal reservoirs will last billions of years. While fossil fuels have an expiry date, renewable sources like geothermal energy is not going to expire anytime soon.
  • Potential capacity – Estimates for the potential of geothermal power plants vary between 0.035 to 2 TW.
  • A stable resource – The power output of a geothermal plant can be accurately predicted. Not subject to the same low-energy fluctuations as with solar or wind.
  • Great for Heating/Cooling – There is significant growth in the number of homeowners utilizing geothermal heating/cooling over the last couple of years.
  • No fuel required – After installation, no mining or transportation activity is necessary.
  • Small land footprint – Smallest land footprint of any major power source.
  • Stable resource – Can provide base load or peak power.
  • Economic factors – Cost-competitive in some areas.
  • Accessibility – Some level of geothermal energy available most places.
  • Renewable – Geothermal energy is extracted from earth’s core and will be available as long as earth exists. It is therefore renewable and can be used for roughly another 4-5 billion years.
  • Abundant Supply – With geothermal energy, there are no shortages or other sorts of problems which sometimes occur with other types of power.
  • Significant Savings for Home Owners – There has been a tremendous increase in the number of homeowners who want to utilize geothermal energy for heating and cooling purposes. The result is that less energy is used for heating homes and offices which results in significant savings for home owners. After the initial expense, a 30-60% savings on heating and 25-50% savings on cooling can cover that cost within few years.

Geothermal Energy Disadvantages

  • Potential emissions – Greenhouse gas below Earth’s surface can potentially migrate to the surface and into the atmosphere. Such emissions tend to be higher near geothermal power plants, which are associated with sulfur dioxide and silica emissions. Also, and the reservoirs can contain traces of toxic heavy metals including mercury, arsenic and boron.
  • Surface Instability – Construction of geothermal power plants can affect the stability of land. In January 1997, the construction of a geothermal power plant in Switzerland triggered an earthquake with a magnitude of 3.4 on the Richter scale.
  • High cost for electricity – Total costs usually end up somewhere between $2 – 7 million for a 1 MW geothermal power plant.
  • High up-front costs for heating and cooling systems – While there is a predictable ROI, it will not happen quickly.For an average sized home, installation of geothermal heat pumps costs between $10,000 – $20,000 which can pay off itself in another 5-10 years down the line
  • Location Specific – Good geothermal reservoirs are hard to come by. Iceland and Philippines meet nearly one-third of their electricity demand with geothermal energy. Prime sites are often far from population centers.
  • Distribution costs – If geothermal energy is transported long distances, cost can become prohibitive.
  • Sustainability questions – Some studies show that reservoirs can be depleted if the fluid is removed faster than replaced. This is not an issue for residential geothermal heating and cooling, where geothermal energy is being used differently than in geothermal power plants.
  • Cost of Powering the Pump – Geothermal power plants are expensive to create and not always that easy to find. And the initial cost for buildings or houses using a geothermal heating and cooling system is expensive and without a fast payback.

Images: The Strokkur Geyser erupting via Shutterstock; Earth’s interior via EnergyKids;

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About the Author

is a writer, producer, and director. Meyers is editor and site director of Green Building Elements, a contributor to CleanTechnica, and founder of Green Streets MediaTrain, a communications connection and eLearning hub. As an independent producer, he's been involved in the development, production and distribution of television and distance learning programs for both the education industry and corporate sector. He also is an avid gardener and loves sustainable innovation.