Geothermal energy is a renewable energy resource. It involves harnessing heat stored under our feet, i.e. inside the Earth’s surface. It can be used at a large scale (utility-level) to generate electricity, but also at a smaller scale in homes and businesses in order to provide heating and cooling,

Geothermal energy has been exploited for a long time, but isn’t as well known as other alternative energy sources such as solar and wind power. 

To help you learn more about this power source, we’ve put together a short overview of its most important benefits and downsides; you can also find more in-depth information further down the page.

Note: This list is based on the two main ways we harness geothermal energy today: Electricity generation with geothermal power plants and geothermal heating and cooling systems.

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The pros and cons of geothermal energy 

Pros and cons of geothermal energy
Pros Cons
Generally environmentally friendly; does not cause significant pollution Some minor environmental issues
Renewable and sustainable Sustainability relies on reservoirs being properly managed
Massive potential Location-specific
Reliable High initial costs
Great for heating and cooling Can cause earthquakes in extreme cases

What is geothermal energy?

The Earth’s crust is made of rocks and water, and a layer of hot molten rock (magma) below that. Magma is very hot – hotter even than the surface of the sun.

The heat produced by magma is a massive source of energy, and it can be converted into electricity. To do this, we drill down into the earth and as a general rule, the lower you go, the hotter it gets. 

The subterranean heat is used to heat water, which turns into steam. That steam is then used to spin a turbine located above the ground, which produces electricity for the grid. 

Geothermal is a renewable source of energy that is almost completely pollution-free, and is consistently reliable. 

Advantages of geothermal energy

1. Environmentally friendly 

Geothermal energy is generally considered environmentally friendly. 

The carbon footprint of a geothermal power plant is minimal. An average geothermal power plant releases 99% less carbon dioxide (CO2) for every megawatt-hour (MWh) of electricity it generates, according to the EIA. 

While there are a few polluting aspects of harnessing geothermal energy, these are minor when compared to the pollution associated with conventional fossil fuel sources such as coal and natural gas. 

Further development of our geothermal resources is considered helpful in the fight against global warming.

2. Renewable and sustainable 

Geothermal reservoirs come from natural resources and are naturally replenished. Geothermal energy is therefore a renewable energy source.

“Sustainable” is another label used for renewable sources of energy. In other words, geothermal energy is a resource that can sustain its own consumption rate – unlike conventional energy sources such as coal and fossil fuels. 

According to scientists, the energy in our geothermal reservoirs will literally last billions of years.

3. Massive potential 

Worldwide energy consumption is currently about 17 terawatts (TW) of power from all sources, both fossil and renewable. 

While that may sound like a lot, there’s actually many times more energy than that stored inside the Earth! That said, most geothermal energy is difficult and/or unprofitable to access. Realistic estimates for the potential of geothermal power plants vary between 0.035 to 2 TW.

Geothermal power plants across the world currently deliver just 12.7 gigawatts (GW) of electricity, with installed geothermal heating capacity a bit higher at 28 GW. This means there is a lot of scope for additional geothermal energy generation. 

4. Stable

Geothermal energy is a reliable source of energy. 

We can predict the power output of a geothermal power plant with remarkable accuracy. This is not the case with solar and wind, where weather plays a huge part in power production. Geothermal power plants are therefore excellent for meeting the baseload energy demand.

Geothermal power plants have a high capacity factor — actual power output is very close to total installed capacity.

The global average power output was over 80% (capacity factor) of total installed capacity in 2017, but as much as 96% has been realized.

5. Great for heating and cooling 

Generating electricity with geothermal energy requires high water temperatures — of more than 150°C (about 300°F) or greater — in order to effectively turn the power-generating turbines.

The other, easier way to utilize geothermal energy is to use it for heating and cooling. This approach makes use of the (relatively small) temperature difference between the surface and a ground source. 

Earth is generally more resistant to seasonal temperature changes than air. Consequently, the ground only a few feet below the surface can act as a heat sink/source with a geothermal heat pump — much in the same way an electrical heat pump uses the heat present in the air..

We’ve seen a tremendous growth in the number of homeowners that utilize geothermal heating/cooling in the last couple of years.

Disadvantages of geothermal energy 

1. Environmental issues 

There is an abundance of greenhouse gases below the surface of the earth. When geothermal energy is used, some of these gases escape towards the surface and into the atmosphere. These emissions tend to be higher near geothermal power plants.

Geothermal power plants generate small amounts of sulfur dioxide and silica emissions. The reservoirs can also contain traces of toxic heavy metals including mercury, arsenic, and boron.

That said, the pollution associated with geothermal power is very low, and just a tiny fraction of what we see with coal power and fossil fuels. Furthermore, there have been no reported cases of water contamination from geothermal sites in the US, according to the Union of Concerned Scientists.  

2. Surface instability (earthquakes) 

Construction of geothermal power plants can affect the stability of land. In fact, geothermal power plants have led to subsidence (sinking of the Earth’s surface) in both Germany and New Zealand.

Earthquakes can be triggered due to hydraulic fracturing, which is an intrinsic part of developing enhanced geothermal system (EGS) power plants.

In 2006, the construction of a geothermal power plant in Switzerland triggered an earthquake with a magnitude of 3.4 on the Richter scale.

3. Expensive 

Commercial geothermal power projects are expensive. Total installation costs usually end up somewhere between $2.5–5 million for a geothermal power plant with a capacity of 1 megawatt (MW). 

The exploration and drilling of new reservoirs plays a big role in driving up costs, and typically accounts for half of total costs.

As previously mentioned, most geothermal resources cannot be utilized in a cost-effective manner, at least not with current technology, level of subsidies, and energy prices.

The upfront costs of geothermal heating and cooling systems for homes and commercial buildings are also steep. That said, these systems are likely to save you money years down the line, and should therefore be regarded as long-term investments. Ground source heat pumps typically cost $15,000–$40,000 installed, and generally have a payback time of 10–20 years.

4. Location specific 

Good geothermal reservoirs are hard to come by. Some countries have been blessed with great resources – Iceland and Philippines, for instance, meet nearly one-third of their electricity demand with geothermal energy.

If geothermal energy is transported long distances by means of hot water (not electricity), significant energy losses have to be taken into account.

5. Sustainability issues 

Rainwater seeps through the earth’s surface and into the geothermal reservoirs over thousands of years. Studies show that the reservoirs can be depleted if the fluid is removed faster than replaced. 

Efforts can be made to inject fluid back into the geothermal reservoir after the thermal energy has been utilized (the turbine has generated electricity).

Geothermal power is sustainable if reservoirs are properly managed. This is not an issue for residential geothermal heating and cooling, where geothermal energy is being used differently than in geothermal power plants.

Geothermal: a clean energy source held back by high upfront costs 

The bottom line is this: Geothermal energy is generally regarded as environmentally friendly, sustainable, and reliable. This makes geothermal energy a no-brainer in some places, but heavy upfront costs stops us from realizing the full potential.

How much influence geothermal power will have on our energy systems in the future depends on technological advancements, energy prices, and politics (subsidies). No one really knows what the situation will look one or two decades down the line.

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