Did you know that 10,000 years ago, the first American Indians built their settlements around hot springs in North America? They used this naturally available source of warm water for cooking, bathing and to keep warm . Without knowing, they had been utilizing the immense reservoir of our planet’s internal heat. Heat that is a great source of thermal energy.
Geothermal energy is energy contained beneath the Earth’s crust. A connection of the words ‘geo’ and ‘thermal’ simply refer to the origin of this energy, where ‘geo’ stands for earth and ‘thermal’ for heat.
How did it get there and why?
Let’s find out! Take a journey to the center of the Earth with us.
Is the Master out of his mind?’ she asked me.— Jules Verne, Journey to the Center of the Earth
‘And he’s taking you with him?’
I nodded again.
‘Where?’ she asked.
I pointed towards the centre of the earth.
‘Into the cellar?’ exclaimed the old servant.
‘No,’ I said, ‘farther down than that.
What is geothermal energy?
Geothermal energy comes in the form of heat produced within the Earth. One part of this heat originates from the time of the formation of our planet 4.6 billion years ago and the other part is constantly generated from the decay of radioactive elements such as uranium and thorium commonly found in rocks .
This internal heat drives powerful geological processes such as continental drifts and volcanic eruptions, but at the same time provides enormous amounts of renewable energy.
How is geothermal energy produced?
Hot springs, mud pots, steam vents, geysers are all natural outlets of geothermal energy. In these places the Earth’s crust is thinner, so the inner heat reaches the surface and makes astonishing displays to demonstrate the power of nature. It was in these geologically active areas, where the idea of taking advantage of this natural energy was first implemented.
Later, with the greater knowledge of geology and availability of sophisticated mapping tools, we have learned to find geothermal reservoirs located even miles underground. In these areas, geothermal power plants are built to capture the heat and use it directly for heating our buildings or to generate electricity for adjacent communities.
Geothermal power plants work on the same principle as other power plants – they use hot steam to run electric turbines. The steam is derived either directly from beneath the earth’s crust, or from water injected into the searing underground.
Geothermal power is a clean source of energy that could become one of the pillars of our sustainable future. But like any other source of energy we are about to exploit, it comes with a number of benefits and concerns at the same time.
Keep on reading to learn about pros and cons of geothermal energy.
Advantages of geothermal energy
#1 Well-established technology with great potential
The era of large-scale use of geothermal energy for heating and electricity has started with the construction of the first geothermal power plant 100 years ago in Tuscany, Italy. The progress was unfortunately hindered by the Second World War, which diverted the world’s attention to more pressing problems, but the post-war recovery came hand in hand with the era of the modern geothermal technology.
In 2015, the total installed geothermal capacity accounted for 13.2 gigawatts, with United States, the Philippines and Indonesia as the top countries on the list. In the case of countries like the Philippines and Indonesia, located in the Ring of Fire, easily accessible geothermal power has become an advantageous substitute for the natural deficiency of fossil fuels.
According to the World Energy Council, the accessible geothermal reserves store incredible amounts of yet untapped energy. An estimated global potential ranges between 35 to 200 gigawatts – up to 15 times more than the current generation capacity.
#2 Abundant and more affordable energy source for geologically-active locations
Geothermal energy can be found everywhere on Earth, but some locations have much larger geothermal energy reserves than others. Over 70 percent of the geothermal energy infrastructure is built along tectonic plate boundaries and hot spots. These geologically active locations are ideal for the utilization of geothermal power.
Interestingly, nearly half of them are islands. For example, Iceland located at the junction of the Eurasian and the North American tectonic plate obtains 66 percent of energy for heating and electricity from its geothermal reservoirs . The Big Island of Hawaii (Puna) is located on the top of a large hot spot and it gets 30 percent of its electricity from a single geothermal power plant [4,5].
Geothermal power is also significantly cheaper for many of these countries. Until 1973, Iceland was almost entirely dependent on oil to heat its houses. Then came the first oil crisis, when prices of oil skyrocketed and Icelanders decided to tap into their own natural riches. That’s when the majority of households switched to geothermal heating. This transition has proven to be as much as five times cheaper for Icelanders than heating with oil .
#3 Renewable and environmentally-friendly resource
Geothermal energy is renewable. The Earth’s internal heat is constantly replenishing from the radioactive decay of unstable elements and is expected to keep doing so for billions of years to come. The heat is radiating towards the surface where it can fuel power plants for as long as the natural recovery rate of this resource is not exceeded.
John W. Lund from the Stanford University believes that properly managed (not overexploited) geothermal power plants could easily supply a steady amount of power for more than 100 years.
Geothermal power plants do not burn fuel like fossil fuel or nuclear power plants. This reflects in their low environmental impact.
In fact, geothermal power releases minimum emissions compared to fossil fuel plants. Geothermal Energy Association states in their assessment that every year geothermal power prevents emissions of:
- 32,000 tons of nitrogen oxide,
- 78,000 tons of sulphur dioxide,
- 17,000 tons of particulate matter,
- 16,000,000 tons of carbon dioxide.
These numbers show the impressive potential of geothermal power to minimize air pollution and help mitigate climate change.
Another environmental benefit is the prevention of habitat destruction. Since geothermal power plants run entirely from the steam generated by the Earth’s natural heat, mining for more resources is not required. Mining non-renewable fossil fuels and uranium, on the other hand, has caused throughout the history some of the worst cases of destruction and contamination of our natural resources.
Geothermal power together with other clean sources of energy could replace these environmentally-destructive sources of energy. Throughout the last decade, geothermal electricity in the United States has substituted the consumption of 25 million barrels of oil and 6 million tons of coal per year .
#4 Stable and predictable energy source
Unlike solar and wind energy technologies, the temperature of the Earth is consistent and predictable despite constantly changing weather conditions. Geothermal energy will produce an expected amount of power 24 hours a day, 7 days a week, 365 days a year regardless of fluctuating weather or changing seasons.
Such level of predictability makes this source of alternative energy a perfect candidate for providing the base load power. Base load power plants constantly produce electricity. These highly efficient power plants run nonstop and are designed to cover around 30 to 40% of the electricity demand throughout a year.
The remaining demand is supplied by peaking power plants which run only when larger amounts of energy are needed – during the day business hours for example. At the moment, most of the base load power is fueled by coal or nuclear energy.
#5 Energy price stabilizer
The stable flow of geothermal energy without the extra costs of extraction, processing and purchase of the actual fuel, acts as a price stabilizer. Its price does not fluctuate like the price of fossil fuels. The largest costs involved with harnessing geothermal energy are paid during the construction of a power plant.
Once the plant is set up, it’s fueled for free. This unique characteristic makes the costs of deploying this form of energy stable over the years.
#6 Technology improvements
With the threat of climate change and fossil fuel deposits running out, many scientists are dedicated to finding more efficient clean energy alternatives. Geothermal technology is one of the promising candidates to reliably power our growing economies. Therefore, the race to improve the effectivity of the applied methods in the industry is ongoing.
The most costly aspect of a geothermal power plant construction is the drilling operation, during which difficulties like extreme temperature, pressure or crystalline rock formations represent significant obstructions. That is where the latest technological advancements are the most helpful. New drills made of high-temperature and pressure resistant materials allow drilling even into previously inaccessible reservoirs .
A new research already taps into the utilization of volcanic geothermal energy. In 2016, scientists have begun drilling into the volcanic system of the Reykjanes Peninsula in Iceland to determine the energy generating potential of magma.
When magma meets water directly, water reaches a “supercritical state.” It is neither a liquid nor gas. In this state, water can carry 10 times more thermal energy than normal steam. By taking advantage of this phenomenon, we could generate more energy using less resources. The research is still in its early stages, so we have to wait to find out if this technique proves to be safe and economically-viable.
#7 Small land use
Since geothermal systems are built mostly underground, they require a minimal area of land for their construction. Geothermal power takes on average one to eight acres per megawatt, while coal power plants need 19 acres per megawatt (without counting the additional land used for mining) .
Geothermal power plants use even eight times less space than solar farms and three times less than wind energy farms .
#8 Heating and cooling potential
The geothermal heat pumps used for heating and cooling of buildings do not burn any fuels nor emit greenhouse gases to maintain a comfortable temperature indoors. These systems work based on the natural temperature difference between the underground and above the ground.
In the winter, the system pumps the Earth’s internal heat to the building and heats it up. In the summer, the system absorbs the heat from inside the building and transfers it underground where it cools down. Colder air is then pumped back into the building to lower the temperature of the indoor air.
This method of temperature control inside the buildings is extremely energy efficient. With a 500 percent efficiency rate, geothermal heating surpasses by far the 98 percent efficiency of gas furnaces .
Geothermal energy can transform people’s lives in remote locations – as a project in the village of Chumathang in North-western Himalayas demonstrates. In the collaboration with Norwegian researchers, a geothermal heating system was set up in a local hotel to maintain indoor temperature at 20 degrees Celsius (68 °F). The system has proven to work well and efficiently.
This is considered a big success because winter temperatures in the area commonly drop below minus 20 degrees Celsius (-4 °F), and due to the shortage of electricity and wood to burn, people often struggle with keeping their houses warm .
#9 Good long-term investment
Although both commercial and residential geothermal systems require a large up-front investment, the energy that is generated from them is free, and therefore allows for an efficient payback.
When return on investment is considered, residential geothermal systems do not cost much more than conventional heating and cooling systems.
Disadvantages of geothermal energy
#1 Location specific
The biggest disadvantage of geothermal energy is that it’s location specific. In many regions, the heat radiating towards the surface is insufficient to generate enough power or to be worth the investment into building a geothermal infrastructure.
Where the Earth’s crust is thick, the geothermal gradient is only 16 degrees Celsius (60 °F) per square kilometer, but in places where the crust is thin, this number rises up to 90 degrees Celsius (194 °F) . The only sites worth considering for the construction of geothermal power plants are the ones with easily accessible geothermal reserves.
#2 Low efficiency of geothermal power plants
Geothermal power plants have lower efficiency than fossil fuel or nuclear power plants. Efficiency expresses the amount of generated electricity from the excavated heat. While efficiency of fossil fuel or nuclear power plants lies between 30 to 40 percent, geothermal power plants reach on average only 12 percent.
Because of the unique character of geothermal heat, which is not emanating with the same intensity in different locations, each geothermal plant has its specific efficiency. For example, a geothermal plant in Darajat, Indonesia, achieves 21 percent efficiency while a place like Chena Hot Springs, Alaska, reaches only one percent conversion efficiency .
#3 Energy loss during transport
Significant energy losses occur when hot water is used to transport the geothermal-generated energy long distances from geothermal plants. This is also another reason why building a power plant is not economically-viable in areas where geothermal reservoir is located too far from communities.
The longer the distance geothermally heated water has to travel through the pipes, the higher amount of energy is getting lost during the process.
#4 Environmental implications
Energy generation from geothermal reserves does not emit greenhouse gases, but greenhouse gases like carbon dioxide and methane are naturally located below the Earth’s surface. These gases can escape into the atmosphere from the geothermal fluid during the drilling.
Even if the risk of releasing these subsurface gases into the atmosphere exists, most geothermal power plants draw their energy from reservoirs with low concentrations of greenhouse gases or apply mechanisms to prevent their escape. In general, geothermal power still emits much lower amounts of greenhouse gases than plants burning fossil fuels.
Other environmental pollutants linked with the utilization of geothermal power are sulfur dioxide, silica emissions, and heavy metals such as mercury, nickel and arsenic. The industry has implemented the technology to reduce the release of these pollutants, but according to the Geothermal Energy Association, the Geysers geothermal facility in California still releases some mercury emissions into the environment .
#5 Geothermal plants can cause earthquakes
Geothermal power plants have to be located in geologically active areas to gain easy access to the Earth’s internal heat. These areas are often more prone to earthquakes.
The industry’s technique of pumping pressurized water underground (similar to hydraulic fracturing when drilling for natural gas) is known for increasing the frequency of seismic activity in the area.
In Salton Sea Geothermal Field in California, researches have observed a clear link between anthropogenically caused earthquakes and geothermal operations. While most earthquakes are generally small, one of them has reached a magnitude of 5.1. Researchers believe that in some locations geothermal power plants might trigger even much more damaging earthquakes .
#6 Conflicting with the natural heritage sites and the rights of indigenous peoples
Beneath the stunning natural spectacle of geysers and hot springs in the Yellowstone National Park lies the enormous magma chamber of one of the biggest volcanos on earth. This area seeps around 6 gigawatts of thermal energy into the atmosphere .
While the geothermal potential of this area is immense, so is its intrinsic natural value for being one of the biodiversity rich places where unique geological activity can be witnessed. That is why the Yellowstone National Park is protected against the geothermal energy exploitation .
Many geologically active sites that would be suitable for large-scale geothermal power operations also represent sacred sites of indigenous people. Therefore, the proliferation of the energy industry in these places is in contradiction with the rights of these people.
One such example is the third largest geyser field in the world – El Tatio in Chile. In 1970s, a number of wells to access its geothermal riches were drilled in El Tatio, but tapping into the geothermal reservoir has led to the disappearance of some geysers. In 2009, an incident happened when one drilling well blew out, generating a 60 meters high steam fountain. The incident has sparked the opposition of local Atacameno people to further geothermal exploitation in the area .
#7 High initial costs
Because the costs of constructing geothermal energy systems and plants are high, geothermal energy systems require a long-term investment strategy. According to the Geothermal Energy Association, the cost of drilling, analyzing and setting up the geothermal infrastructure is around $3,400 per kilowatt of power in the United States and could be compared with the high costs of nuclear power.
To build a geothermal power plant is around 60 percent more costly than building a natural gas plant . But the costs of running a geothermal plant are cheaper because it does not require fuel. The office of Energy Efficiency & Renewable Energy estimates that the operation of such a plant costs on average $0.01 to 0.03 per kilowatt hour .
In the end, the long-term cost of geothermally produced energy is comparable to the cost of a natural gas or coal plant .
#8 Reservoirs need proper management
Geothermal energy is sustainable only if the reservoirs are properly managed. If they are overused, geothermal energy reservoirs can be depleted much faster than they are replaced and the power plants would literally “run out of steam.”
In Iceland, some environmentalists and geologists start to sound the alarm that if the country continues drawing the same amounts of geothermal energy as it does now, some of the reservoirs might run dry in the next 50 to 100 years. Then, they will take at least another 100 years to replenish again .
Geothermal energy overall is a renewable resource, but it can get depleted locally if power plants use excessive amounts. For example, the Geysers geothermal field in California has been exploited with great success since 1960s, but in 1988 its maximum production rate was reached and since then its output have been steadily declining .