What Is Geothermal Energy?

Geothermal resources are not a recent discovery; they have been used for thousands of years for heating and cooking. It was first utilised for electrical purposes in 1904 when Piero Ginori Conti, an Italian scientist, used it to activate an electronic generator. There are currently geothermal plants in over 80 countries, including the US, Turkey, New Zealand, Mexico, and Iceland. The word geothermal perfectly describes what it is, being a combination of the Greek words ‘geo’, meaning earth, and ‘therme’, meaning heat.

Where Is Geothermal Energy Found?

Geothermal resources can be found between shallow ground right down to the magma located in the mantle layer of the earth. It is normally extracted from water reservoirs found a few miles below the earth’s surface that has been heated by the magma below.

In terms of geography, geothermal resources can be located nearby the boundaries of the earth’s tectonic plates. At these boundaries, magma tends to be closer to the earth’s surface, which creates these hot water reservoirs. One of the biggest areas of geothermal heat activity is the perimeter of the Pacific Ocean, which has garnered the name ‘the Ring of Fire’.

Many major geothermal sources have already been located, and power plants have been constructed above them. This includes such locations as the Geysers Geothermal Complex in California, the Larderllo Geothermal Complex in central Italy, and the Cerro Prieto Station in Baja California, Mexico.

There are 3 different designs of geothermal power plants, each of which uses steam to turn a turbine that activates electricity generators. The steam comes from the reservoirs located several miles below the surface of the earth. Each type of power plant has its own unique method of extracting steam.

Once the steam has been used to generate electricity, it is condensed into hot water and fed back into the ground where it can be used again. This makes geothermal power extraction highly sustainable.

The 3 Different Designs of Geothermal Power Plants

Dry steam

Dry steam power plants use pipes that lift the geothermal steam out of the underground reservoirs, which is then fed into turbines. The steam turns these turbines, activates the generator, and produces electricity.

This is the oldest type of geothermal power plant and is still widely used today.

Flash plants

Like dry steams, flash plants pipe directly down into the underground reservoirs. However, instead of extracting steam, flash plants extract hot water. This hot water is pumped to the surface and fed into a flash tank. This flash tank is kept at a low temperature, which turns the water into steam as soon as it arrives in the tank.

Like dry steam plants, the steam produced is then used to set the turbines in motion, which activate the generator. Flash plants are the most common type of geothermal plant in use today.

Binary plants

Binary plants differ from the former two plants, as the extracted resources never come into direct contact with the turbines. Water is still pumped the same as in a flash plant, but instead of being flash converted, it enters into a heat exchanger. In the heat exchanger, a second liquid is heated, which turns into steam and powers the turbines.

Pros:

Environmentally friendly

The main advantage of geothermal energy is that it does more good for the environment than bad. It does not involve the burning of fossil fuels and produces a lower carbon footprint than conventional energy sources that are in use today.

The heat extraction of geothermal resources produces relatively low emissions, however, the exploitation of its resources can lead to greenhouse gas emissions.

Renewable

Geothermal heat will be able to renew itself forever. Heat is perpetually produced inside the earth’s core, which will continue to heat trapped water in porous rock, and continue to be an accessible source of energy. As long as a steady flow of water is pumped back down into the underground reservoirs, a geothermal plant could hypothetically last forever.

Extremely reliable

Unlike wind, biomass, and solar power, geothermal heat is constant and does not rely on certain conditions to produce power. This makes it one of the most reliable sustainable energy sources available, next to hydropower.

Check out our other guides on green energy sources and their potential here.

Enormous potential

As more countries switch to greener energy sources, geothermal energy is likely to gain more attention than it currently has. More focus will bring better extraction technology and a better understanding of how to fully harness geothermal power.

The energy source still has a lot of unexplored potential, which could help to overcome some of the cons it currently faces. For example, it may be possible to one day extract geothermal energy directly from the magma, if the right technology is developed.

Geothermal power plants require little maintenance

There are only a few moving parts involved in each power plant, rendering them low maintenance. Although building a geothermal resource plant is expensive to begin with, they come with relatively low operating costs.

Cons:

Sustainability

Although considered to be a sustainable energy source, the water used needs to be pumped back down to the reservoir to keep energy levels steady. This needs to be completed at a faster rate than the water extraction process.

High costs

Although they are low-maintenance in the long run, the initial cost of setting up a geothermal renewable energy plant is high. It’s far cheaper to set up a coal, gas, or oil plant than it is to set up geothermal projects.

Risk of triggering earthquakes

An excessive amount of drilling into the surface of the earth, particularly nearby the boundaries of tectonic plates, could trigger an earthquake. The risk of this occurring is increased when water is used to widen fissures in the earth’s crust, which is sometimes done to make the extraction of geothermal resources easier.

Environmental issues

When digging for geothermal resources, several greenhouses gasses are released into the atmosphere. These emissions would get released eventually, however, the process is sped up when digging holes into the earth. This includes the likes of carbon dioxide, methane, ammonia, and sulfide.

However, the level of emissions released during the extraction of geothermal resources is far lower than the amount caused by the burning of fossil fuels.

Restricted to certain locations

Geothermal energy can’t be extracted from anywhere. Geothermal reservoirs only exist in certain places, and some of them may not even be accessible for extraction. Additionally, some locations may be accessible but are off-limits for other reasons. For example, some geothermal locations may be found in a nature reserve.

For example, in the US, the only two steam depositories are located at the Geysers in northern California and Yellowstone National Park in Wyoming. The former is where the U.S.’s geothermal plants are located, the latter is a legally protected National Park, which does not permit commercial energy activity.

The spread of geothermal harnessing has been moving at a slow speed. The global installed capacity has only jumped minorly between 2010 and 2019 and is currently not on track to reach the Sustainable Development Scenario (SDS).

This partially comes down to the location restrictions associated with enhanced geothermal systems. Iceland can achieve 25% of its electricity production through geothermal technologies because it has so many geothermal power resources available.

There is currently a lack of geothermal power in Britain due to a lack of plants and available areas where geothermal extraction would be possible. However, there are signs that there will be more plants in the future. In the meantime, it is possible to install a geothermal heat exchanger for home use, which could make your energy use greener and more cost-effective.

Use our Business Energy Comparison feature to find out other means of making your business’ energy use more cost-effective.