Geothermal Energy: What It Is & How It Works

Visitors to Old Faithful in Yellowstone National Park get a front-row seat at a geothermal energy showcase in action. From this geyser, they soon discover there is much to learn from forces contained below the Earth’s crust.

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Old Faithful basin in Yellowstone National Park

What is geothermal energy?

This straightforward description comes from the Geothermal Energy Association (GEA).

“Heat has been radiating from the center of the Earth for some 4.5 billion years.  At 6437.4 km (4,000 miles) deep, the center of the Earth hovers around the same temperatures as the sun’s surface, 9932°F (5,500°C).  Scientists estimate that 42 million megawatts (MW) of power flow from the Earth’s interior, primarily by conduction.

“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.”

Ultimately, this is a wonderful source of clean, renewable energy. Plus it is sustainable, at least for as long as our Earth is here.

The Yellowstone example

old faithful geyser shutterstock_206238349 (1)According to Wikipedia, there are numerous and varied geothermal energy areas of Yellowstone, including geyser basins such as Old Faithful, plus hot springsmud pots, and fumaroles. In fact, some 10,000 geothermal features exist in Yellowstone.

Although famous large geysers like Old Faithful are part of this total number, most of Yellowstone’s geysers are relatively small, erupting only one or two feet high. The hydrothermal system supplying these geysers is heated by the underlying Yellowstone hotspot, The hotspot’s most recent super eruption took place 640,000 years ago, creating the Lava Creek Tuff and Yellowstone Caldera, which now erupt at the surface as geysers, hot springs, and fumaroles.

GEA basics_clip_image002_0005Geyser water is extremely hot. Water from these geysers registers above the boiling point, averaging 204 °F (95.5 °C). But the water cools significantly while airborne. By the time it comes back to the ground, it is no longer scalding hot. Still, this hot water is nothing to joke about. Several deaths have occurred in the park as a result of falls into hot springs.

In the US, most geothermal reservoirs of hot water are found in the western states, plus Alaska and Hawaii. Wells can be drilled into these underground reservoirs for the generation of electricity. Some geothermal power plants (there are three kinds) use the steam from a reservoir to power a turbine and generator, while others use the hot water to boil a working fluid which vaporizes and then turns a turbine.

Hot water near the surface of Earth can also be used directly for heat. Direct-use applications include heating buildings, growing plants in greenhouses, drying crops, heating water at fish farms, and several industrial processes such as pasteurizing milk.

→ Also recommended: Geothermal Energy Advantages And Disadvantages

→ Also recommended: Geothermal Energy Facts

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According to NREL, many technologies have been developed to take advantage of geothermal energy. This heat can be drawn from several sources: hot water or steam reservoirs deep in the earth that are accessed by drilling; geothermal reservoirs located near the earth’s surface, mostly located in the western U.S., Alaska, and Hawaii; and the shallow ground near the Earth’s surface that maintains a relatively constant temperature of 50°–60°F.

This variety of geothermal resources allows them to be used on both large and small scales. A utility can use the hot water and steam from reservoirs to drive generators and produce electricity for its customers. Other applications apply the heat produced from geothermal directly to various uses in buildings, roads, agriculture, and industrial plants. Still others use the heat directly from the ground to provide heating and cooling in homes and other buildings.

Three Geothermal Technologies Are Being Used

[1] Geothermal Electricity Production
 – Steam is produced from reservoirs of hot water found a couple of miles or more below the Earth’s surface. The steam  rotates a turbine which activates a generator, which then produces electricity. There are three types of geothermal power plants: flash steam, dry steam, and binary cycle.

  • Flash steam power plants are the most common. They use geothermal reservoirs of water with temperatures greater than 360°F (182°C). This hot water flows up through wells in the ground under its own pressure. As the water 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 and generator. Leftover water and condensed steam are injected back into the reservoir, making this a sustainable resource.
  • Dry steam power plants account for approximately 50% of installed geothermal capacity in the US and are located in California. Dry steam power plants draw from underground resources of steam. The steam is piped directly from underground wells to a power plant, where it is directed into a turbine/generator unit. There are only two known underground resources of steam in the US: The Geysers in northern California and Yellowstone National Park in Wyoming. Since Yellowstone is protected from development, the only dry steam plants in the country are at The Geysers in California.
  • Binary cycle power plants operate on water at lower temperatures of about 225°-360°F (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.

Proponents believe small-scale geothermal power plants (under 5 MW) have the potential for widespread application in US rural areas. Power plants like these can be built in the western states, Alaska, and Hawaii.

Here is the current list of geothermal power plants in the world.

[2] Geothermal Direct Use
 – In modern direct-use systems, a well is drilled into a geothermal reservoir for creating  a steady stream of hot water. The water is brought up through the well into piping. It then enters a heat exchanger, where it then directly delivers heat. 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. 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.

[3] Geothermal Heat Pumps
 – According to GEOExchange, geothermal heat pumps are self-contained units which heat and cool homes and commercial buildings. They also while provide hot water. They use standard electronic thermostats and duct systems, making them appropriate for retrofits of standard heating, ventilation and air conditioning systems.

Gaining in popularity, geothermal heat pumps can be sized to heat and cool any building in any climate. They are reported to use less energy than conventional heating systems, since they draw heat from the ground. They also reduce air pollution.

March 17: 2016 US & International Geothermal Showcase

This March 17th, the GEA will conduct the 2016 US & International Geothermal Showcase in Washington DC, a one-day event focusing on successful geothermal projects.

“With demand for clean electricity on the rise, international attention has turned to geothermal energy with a highlight being the declaration of 38 countries forming the Global Geothermal Alliance at the Paris Climate Conference. Building on this momentum, the Geothermal Energy Association’s (GEA) US and International Geothermal Showcase this March will highlight to Washington DC decision makers how leading geothermal nations are unlocking geothermal potential.

In addition to the US, 22 countries will be represented at the event. They include the UK, Burundi, Indonesia, Italy, Ethiopia, Uganda, Kenya, Mexico, Qatar, Nairobi, Japan, Philippines, Fiji, Costa Rica, Papua New Guinea, Samoa, Solomon Islands, Tonga, Vanuatu, and Nevis.

The Showcase will highlight key geothermal projects, trends, and governmental policies in the US and the international markets. Topics include:

  • Geothermal market today
  • Projects under development in the US and internationally
  • Outlook for the future of the geothermal market
  • Policies driving geothermal development
  • New technologies
  • Federal agency – home and abroad

Expect geothermal energy to be an attractive renewable energy resource in the coming years.

Images: Temperatures of the Earth via GEA; Old Faithful basin via Shutterstock; Old Faithful erupting via Shutterstock

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