What Is Geothermal Energy?
Geothermal energy is heat within the earth. The word geothermal comes from the Greek words geo (earth) and therme (heat).
Geothermal energy is a renewable energy source because heat is continuously produced inside the earth. People use geothermal heat for bathing, for heating buildings, and for generating electricity.
Geothermal energy is thermal energy extracted from the Earth’s crust. It combines energy from the formation of the planet and from radioactive decay. Geothermal energy has been exploited as a source of heat and/or electric power for millennia.
Geothermal heating, using water from hot springs, for example, has been used for bathing since Paleolithic times and for space heating since Roman times.
Geothermal power, (generation of electricity from geothermal energy), has been used since the 20th century. Unlike wind and solar energy, geothermal plants produce power at a constant rate, without regard to weather conditions.
Geothermal resources are theoretically more than adequate to supply humanity’s energy needs. Most extraction occurs in areas near tectonic plate boundaries.
The cost of generating geothermal power decreased by 25% during the 1980s and 1990s. Technological advances continued to reduce costs and thereby expand the amount of viable resources.
In 2021, the US Department of Energy estimated that power from a plant “built today” costs about $0.05/kWh.
In 2019, 13,900 megawatts (MW) of geothermal power were available worldwide.
An additional 28 gigawatts provided heat for district heating, space heating, spas, industrial processes, desalination, and agricultural applications as of 2010. As of 2019 the industry employed about one hundred thousand people.
Advantages of Geothermal Energy
#1. Always available.
Aside from being essentially unlimited like many other renewables, geothermal energy is always available.
It is not impacted upon by whether it is day or night like solar energy, and does not depend on season, climate or weather conditions like wind and solar power.
On average, a geothermal power plant will produce energy for around 8,600 hours a year, while in solar plants the average is around 2,000 hours per year.
We can therefore describe the rate of geothermal energy production as constant, at least in the short or medium term. This makes it more easily predicable and plannable.
#2. Doesn’t require large spaces.
Unlike the majestic expanses of large wind turbines and photovoltaic panels, geothermal power plants only require modest amounts of space.
Regardless of whether it is a domestic system or a large-scale plant, most of the components (including the heat exchangers) are buried underground, with very little remaining above ground.
In homes, the heat pump is about the size of a household appliance, while in larger plants, the biggest components are the cooling towers, followed by turbines.
In certain cases, the plants can have a visual impact on the landscape but newer architectural designs are mitigating this issue.
#3. Silent energy.
At least while functioning at full capacity, geothermal power plants produce negligible and imperceptible noise levels.
During the construction phase of the plants – including excavations – a certain amount of noise is inevitable, but once construction is complete, everything is silent.
This applies to both domestic systems and outside larger power stations that have at most several turbines spinning.
#4. It creates record numbers of jobs.
That is what the data gathered by the energy services manager, GSE, tells us: for the same installed power, geothermal energy creates more indirect employment than any other type of renewable.
In terms of numbers, that translates to 34 jobs per installed megawatt, much higher than the 19 created by wind power and the 12 by photovoltaic energy.
In Italy alone, 2,000 gigawatts of installed power would guarantee permanent employment for 4,000 people and 30,000 other jobs.
#5. Provides more energy for the same nominal power.
Because delivery is constant, geothermal energy can work at full capacity non-stop (maintenance aside). This means that the resulting amount of energy will be the equivalent of the power multiplied by the hours of use.
This is very different to photovoltaic, hydroelectric and wind systems, which only rarely work at full capacity. So, more energy is produced for the same nominal power.
#6. Allows double recycling.
Geothermal power optimizes resources. On the one hand, the plants have components that can be salvaged and reused at the end of the installation’s lifecycle.
On the other, during operation, the flows are organized in such a way as to put any heat that can’t be used immediately back into the circuit using the steam pipes that power the plant, helping to save energy.
#7. The plants are long-lasting, safe and reliable.
Both domestic and large scale plants have very long average life spans – up to 80 to 100 years. This is extraordinary longevity compared to a domestic boiler, which normally lasts around 15 years.
The fact that there are no fuels involved also means there is no risk of fire, and the long experience we have gained with this type of system guarantees excellent reliability.
#8. Requires very little maintenance.
Particularly when it comes to domestic use, geothermal plants do not require any special maintenance. As they are closed systems, the pressure of the fluid in the piping self-regulates, and the number of electrical and mechanical elements that can break down is also very small.
#9. The Earth’s heat can also cool.
When geothermal energy is mentioned, we think first and foremost of thermal energy and heating. Nonetheless, geothermal plants are designed to both heat and cool.
This is why, aside from in the large stations, geothermal power systems can be installed in almost any type of building: from homes to shopping malls, public buildings and sports centers.
The only limit being, of course, that the location is favorable in terms of the characteristics of the Earth’s crust.
#10. More advantages for the home.
In addition to providing air conditioning in the summer and heating in the winter, geothermal energy has many other advantages when used in the home.
For instance, it reduces overall energy consumption by between 30 and 70% because it can also do the job of a boiler, i.e., heat water for use in the kitchen and bathroom.
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).
The construction of geothermal power plants can affect the stability of the 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 play a big role in driving up costs, typically accounting for half of the overall 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.