Geothermal Power Plants

Geothermal technology is a great option for energy production in many locations, especially where it is easily accessible, because it is a clean energy. Around the world, more than 8,900 MW of large, utility-scale plants in 24 countries can provide enough electricity to supply 12 million average American homes annually. In some countries, such as Iceland and the Philippines, geothermal energy accounts for over 25% of their energy supply.

Geothermal Power Plant Location

Where does this energy come from? Below the Earth’s crust is a layer of hot, molten rock called magma. This magma is a huge reservoir of heat that is accessible by digging deep in the earth’s crust. Although the heat is easy to tap into in places such as young (relatively) volcanoes and plate boundaries, it could be tapped into from almost anywhere on the Earth. The U.S. Geological Survey found that the United State’s geothermal resources could one day provide nearly all the nation’s electricity.

The heat from magma is closer to the surface in places with more geological activity (areas with seismic activity), so land stability is an important issue to consider when building geothermal power plants. In Basal, Switzerland, the construction of plant was suspended when more than 10,000 seismic events registering up to 3.4 on the Richter scale occurred during 6 days of drilling down to the heat source.

Below is a map of the US showing optimal geothermal power plant sites.

Map of favorable geothermal power plant locations in the US.

History of Geothermal Power

Geothermal heating has been used since prehistoric times for many different things. The oldest known uses of geothermal energy come from as early as the 3rd century BC in the Lisan Mountain of China at a spa built by the Qin Dynasty, where hot springs were used as a water source. During the 1st century AD, the Romans made use of hot springs at Bath in Somerset, England to create a public bath as well as underfloor heating. The oldest geothermal heating system still in operation is located in Chaudes-Aigues, France, and was built in the 14th century.

In 1827, geysers were used to extract boric acid from the volcanic mud in Lardarello, Italy. America’s first district heating system was developed in Boise, Idaho, in 1892. In 1926, also in Boise, Idaho, a deep geothermal well was used to heat greenhouses. Around this time, geysers were being used in Iceland and Tuscany to heat greenhouses. And in 1904, Prince Piero Ginori Conti built and tested the first geothermal power plant at Lardarello, Italy. It was a success, and lit four light bulbs.

Environmental Impact of Geothermal Power Plants

Nesjavellir Geothermal Power Plant in Þingvellir, Iceland.

Nesjavellir Geothermal Power Plant in Þingvellir, Iceland releases pollution free steam.

The impact to the environment is largely from gas emission escaping from the volcanically active areas where geothermal plants are located. The gasses released during in this type of energy generation can contribute to global warming, bad smells and acid rain when they are released into the atmosphere. Some research is going into sequestering the gasses by pumping them back into the volcanically active geological formation, but the long term effects of this are still unknown. Even though the gasses emitted are the same as the green house gasses emitted in fossil fuel burning, the amount of gas emitted is much less when compared to fossil fuel power production. Keep in mind that direct geothermal heating systems often contain pumps and compressors that use traditional fossil fuels to run. The environmental impact of these types of power generators must be taken into consideration with regard to the emission produced. An additional pollution concern is the water from these geothermal power plants that may contain toxic chemicals such as mercury, arsenic and boron. Again, these chemicals can be pumped back into the earth to reduce their impact on the environment on the surface.

Types of Power Plants

There are three types of geothermal power plants: the dry steam power plant, the flash steam power plant, and the binary cycle power plant.

Dry Steam Power Plant

The dry steam power plant utilizes a well sunk deep into the Earth to make steam from the heated ground. The steam then travels up a pipe, into a turbine, which turns a generator to produce electricity. This is the oldest type of plant used. The first one was built in 1904 in Lardarello, Italy, and is still in use today. It is also used at The Geysers, an American geothermal power plant that is the largest one of its kind in use today.

Diagram of a dry steam geothermal power plant.

Diagram of a dry steam geothermal power plant.

Flash Steam Power Plant

A flash steam power plant pumps super heated water at high pressure up from a deep well and into the plant on the surface. Once the water is in the plant it is brought down to normal atmospheric pressure so it turns to steam that is used to turn turbines. The key is that the water is then cooled and returned down to be heated again at the bottom of the well so energy from active areas without very much water are still able to be harnessed.

Diagram of a flash steam geothermal power plant.

Diagram of a flash steam geothermal power plant.

Binary Cycle Power Plant

The third type of geothermal power plant is the binary cycle plant. This type of plant uses closed loop systems of fluids which limits the emissions from the geological formation. The hot water harnessed from deep in the well is pumped into a heat exchanger where it heats the other liquid into a steam before being returned to the formation to allow it to be reheated. The secondary steam is used to operate the turbines and is also on a closed loop to limit possible emissions.

Diagram of a binary cycle geothermal power plant.

Diagram of a binary cycle geothermal power plant.

Geothermal Power Plants Around the World

Out of 25 countries currently using this type of energy production, the United States boasts the highest capacity of power produced from its geothermal plants. However, it is one of the lowest by percentage of total national energy production. Iceland rates as one of the highest percentage of national production, using geothermal energy for 30% of its national energy production.

Geothermal energy production will prove to be very beneficial to the increasing energy demands of the world because the pollution emissions resulting from these plants are minimal, and the output of energy far exceeds that of traditional fossil fuels. Geothermal power plants also allow nations to place more reliance on their country’s own resources which means less reliance on other countries resource.



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