Fossil fuels have been the primary source of energy for human civilization since the start of the industrial revolution. While coal, oil and natural gas still supply most of the world’s energy, growing concerns about dwindling supplies and the carbon released when these fuels are burned have spurred a search for clean, renewable energy sources. While wind and solar have gotten the most attention, geothermal energy is one of the most efficient and sustainable alternatives to fossil fuels. Unfortunately, it can only be utilized in some locations.

Background on Geothermal Energy

Instead of burning fuel sources, geothermal energy uses heat from inside the Earth to generate electricity. Earth’s core is still hot from the formation of the planet, and it’s made even hotter by the decay of radioactive elements and the friction caused by pliable rock rising and sinking at great depths. This heat is trapped deep inside the planet, but in some locations, it rises close to the surface where it heats up underground reservoirs of water. Wherever there are geysers, hot springs or volcanoes, Earth’s inner heat is close enough to the surface to use.

There are three basic ways that geothermal plants use this heat. The most common type of geothermal plant is a flash steam plant; boiling water from inside the earth is brought to the surface where it is converted to steam, which is used to turn turbines that power generators. The second type, binary cycle power plants, brings hot water to the surface to heat a second liquid with a lower boiling point, which then converts to steam that turns turbines that power generators. The third type is dry steam plants, which use steam directly from the Earth.

In some locations, like Australia, where heat is present close to the surface but there’s no water or steam to extract and the rock is too solid to allow water to percolate through, an enhanced geothermal system, or EGS, can be set up. These systems create fractures in the rock and force water through them so it can be heated and extracted for use. These technologies have made it possible for geothermal energy to be developed in more locations around the world.

Geothermal energy can also be used directly without conversion to electricity first. Temperatures beneath the surface may not be high enough to power turbines, but hot enough to heat homes or be used for industrial heating. In these cases, hot water or steam is piped from the Earth and the heat is directly applied for a variety of uses.

For example, nearly 90% of buildings in Iceland are heated by geothermal waters, including greenhouses used for large-scale agriculture. Because the process is so affordable in Iceland, even some of the capital city’s sidewalks are heated using geothermal waters. Many food processing facilities around the world use geothermal heat to dehydrate and pasteurize food. It is also being used to extract gold from ore, brew beer and grow mushrooms.

Archaeological evidence suggests that humans have been using geothermal energy for at least the last 11,000 years. From the Maori people in New Zealand to the courts of China’s Qin Dynasty and the Roman Empire, geothermal hot springs have been used around the world and throughout history for bathing, cooking and healing and the harvesting of mineral resources. The modern use of geothermal energy to generate electricity began in Larderello, Italy, where the first geothermal dry steam power plant was built in 1904.

Today, geothermal energy accounts for just 0.3% of the global energy supply, but in the places it’s used, it often makes a significant contribution. For example, Kenya gets 44% of its power from geothermal energy, Iceland 27% and El Salvador 26%. The United States is the largest producer of geothermal energy in the world, but it only accounts for 0.4% of all the energy used in the nation. In California, however, where over 75% of the country’s geothermal energy is produced, it accounts for around 6% of the state’s energy supply.

Pros of Geothermal Energy

Geothermal energy has many benefits over fossil fuels like coal, oil and natural gas. It even has advantages over more well-known, renewable energies like solar and wind. Here are the most significant pros of geothermal energy:

  1. Nearly Zero Emissions

When fossil fuels are burned, carbon is released into the atmosphere as carbon dioxide and methane. These greenhouse gases trap heat in our atmosphere, leading to global climate change. The primary advantage of geothermal energy is that nothing is burned, so carbon emissions and other air pollutants are virtually non-existent. Using energy harvested from Earth’s internal heat is a partial solution to climate change.

  1. Minimal Environmental Impact

Geothermal energy has other environmental advantages, too. Because heat is extracted and utilized at its source, there’s no need for environmentally damaging mines, deepwater oil drills or extra emissions from shipping materials from their source to power plants. Geothermal power plants also occupy a very small surface area relative to other types of power plants because much of the plant is underground.

  1. Inexhaustible Resource

In recent years it has become more technically challenging to extract fossil fuels because easily accessible reservoirs have been depleted. The vast size of planet Earth and the immense amount of heat energy contained within it means it is an essentially inexhaustible resource. As long as the Earth exists, heat energy can be harvested from its interior.

  1. Continuous Operation

One of the downsides to renewable energy like solar or wind is that power can’t be continuously harvested. Wind dies down and the sun sets, requiring energy production to halt temporarily. Because the Earth’s interior is always hot, geothermal plants can operate 24 hours a day, 365 days a year. In 2011, when Japan was struck by the biggest earthquake in its history, the Yanaizu-Nishiyama geothermal power plant in Fukushima continued to operate even as other nearby power plants failed.

  1. Stable Pricing

Because of fluctuations in the global market, the cost of fossil fuels can rise and fall from day to day. Often, energy companies increase consumer prices when energy costs rise, but fail to lower them when fuel costs fall again. Because geothermal energy doesn’t rely on combustibles, the cost is not only low but also stable.

Cons of Geothermal Energy

For all its advantages, geothermal energy isn’t perfect. While the list of cons is shorter than the list of pros, they are major enough to put some hard limits on the future expansion of geothermal energy.

  1. Limited Locations

The biggest con of geothermal energy is that it’s really only feasible in places where temperatures are high close to the surface of the Earth. These are places near the edges of tectonic plates or near ‘hot spots,’ locations where hot magma rises close to the surface. In theory, geothermal energy could be developed anywhere, but it would require drilling so deep into the Earth that the set-up costs would be prohibitive. Although there’s a lot of potential for geothermal energy to be developed, it still can’t be developed everywhere.

  1. High Up-Front Costs

Building a geothermal plant can be expensive, more expensive than other types of power plants. Geological exploration to locate heat sources, the drilling of wells and building the plant all require a high initial investment. It’s true that when costs are compared across the lifetime of the power plant, geothermal pays for itself by having low operational costs. However, laying down a huge sum to get a plant up and running may not be politically or financially possible.

  1. Geologic Instability

Geothermal power plants extract and reinject hot fluids into the ground in areas that are already seismically active. This has been found to cause earthquakes. Usually, these are so small that they can only be detected with sensitive seismographs. However, sometimes the impact can be much greater. For example, the city of Basel, Switzerland, was hit with a series of earthquakes in late 2006 and early 2007 caused by the water injected into fractured rock at a new EGS facility. The plant had to be abandoned.

How Does Geothermal Energy Affect Me?

Geothermal energy is likely to grow in the future, and depending on where you live, you may be able to take advantage of it. There is also ongoing research into digging deeper wells to make geothermal energy accessible in more places. Norway is a world leader in developing geothermal energy, largely through the development of deep-well and heat-pump technologies that allow them to make use of lower temperatures beneath the surface.

Can I Get Involved?

Depending on where you live, you may be in a position to install a geothermal heat pump system to heat your home. While Hawaii, California, Oregon, Utah and Nevada have the most well-developed geothermal energy operations, geothermal heat pump systems for home heating have been installed all across the United States. Organizations like The Geothermal Exchange Organization have worked hard to increase government subsidies to 30% of the total system cost to make installation accessible to more homeowners.

While geothermal may never be the sole source of energy for the world, it has the potential to provide clean, inexpensive power in many locations. As the industry matures, safer, more affordable technologies will be developed to minimize the cons and maximize the pros.