Geothermal energy always has had the tag of promising or up-and-coming renewable energy resource forever. The strange part is that it is one of the oldest energy resources tapped by humans, almost 10,000 years ago!
Archeological evidence points to the use of hot springs by indigenous people in America at least 10 millenniums back. Much later, the people of ancient Greece and Rome considered hot springs as sacred places and for healing even as far back as the 5th and 4th centuries BCE.
However, as newer, easier energy resources were discovered, the use of geothermal energy stagnated or even came down. It witnessed a revival in 1818 when François Jacques de Larderel, a French engineer discovered an innovative method for the extraction of boric acid from hot springs. This ultimately led to the construction of a commercial-scale geothermal power plant, a first of its kind in the world.
Only after the end of the Second World War, geothermal energy took root in the United States. Now, it is home to the largest geothermal installation complex in the world, the Geysers, located in the Mayacamas Mountains north of San Francisco. Commissioned in 1960, this complex includes 22 power plants, run on steam from more than 350 wells.
Even among the renewable energy resources, geothermal energy comes with a modest carbon footprint of 38 gms CO2/KWh, which is lower than that of solar energy. So, what is preventing geothermal systems from being adopted on a larger scale?
Read on to learn more about geothermal energy and its pros and cons.
What is geothermal energy?
Underneath the earth’s crust, lies the mantle, almost 2900 kilometers thick and constituting 84% of the earth’s total volume. And, much of the earth’s mantle is magma, which is an extremely hot liquid with molten rock and small amounts of dissolved gasses like sulfur, water vapor, and carbon dioxide.
It is indeed surprising to know that magma is hotter than the surface of the sun. This immense heat energy, if tapped, can be an excellent energy source. Geothermal energy is exactly this heat energy (In Greek, geo means earth and therma means heat).
To tap geothermal energy, deep holes or wells are drilled on the earth’s crust to reach the hot underground water and steam. Typically, these wells can be 1-3 km deep and the temperature of groundwater can be anywhere between 250°C and 300°C and pressure in the range of 600-1200 PSI.
The hot water and steam are pumped to the earth’s surface and used either directly to heat buildings or produce steam to turn turbines, which in turn generates electricity.
The groundwater loses its heat and is allowed to flow back into the earth’s interiors, where it again gets heated up. The process is repeated.
Key facts about geothermal energy
Geothermal energy is:
- The third-largest renewable energy resource, only behind hydropower and biomass energy.
- Ideal for domestic and industrial use
- Useful for heating and generating electricity
- Worldwide, geothermal systems account for 15.4GW, of which 3.68 GW or 23.9% is installed in the United States. This makes the United States the largest producer of geothermal energy in the world.
- The US Geological Survey (USGS) has identified approximately 22 GW of geothermal resources for future development.
Geothermal energy advantages and disadvantages
Geothermal energy is one of the ready-made sources of energy nature has given us. It is clean, green, renewable, and sustainable. It can be the frontrunner as a replacement for fossil fuels like natural gas, coal, and oil.
However, despite all its advantages, geothermal energy is not taking off in the way we expect it to. It is not getting the attention it deserves. Why is that so? It is not all sunshine and rainbows. Geothermal energy disadvantages are a reality.
Let’s go through advantages as well as geothermal power disadvantages in detail and find out the answer.
Advantages of geothermal energy
1. Low carbon footprint
The process of using geothermal energy to generate electricity is environmentally-friendly. Especially when compared with fossil fuel power plants, the carbon footprint of geothermal systems is negligible. Its carbon footprint is as low as 38 gms CO2/kWh.
Harnessing geothermal energy also doesn’t involve too much greenhouse gas emissions. The incredible amount of heat existing in the earth’s interiors is believed to last for billions of years. As we tap the energy, it gets replenished. This makes geothermal energy sustainable and renewable.
2. Reliable source of power
The existence of molten magma in the earth’s mantle is indisputable. Only at certain points on the earth’s crust can this heat energy be tapped. Once these locations are discovered, they can be used to harness geothermal energy for a long time. This makes geothermal systems predictable and reliable.
The reliability of geothermal energy is one of its most prominent advantages, especially when compared with fossil fuels or even other renewable energy resources like solar or wind energy. Both sunlight and wind are intermittent and unreliable in providing us with 24×7 energy. On the other hand, geothermal systems can generate electricity round the clock, 365 days a year.
The reliability of geothermal energy makes it the ideal candidate for meeting baseload electricity demand in utility-scale power plants.
3. Needs less land space
We all know how much land space solar and wind farms take up, rendering the land unsuitable for anything else. Geothermal energy power plants, on the other hand, take up much less land space. The reason is simple enough. The heat energy comes ready for use from the earth’s interiors. All we need to do is pump the heat to the surface of the earth and put it to good use. This doesn’t need any elaborate setup like that of solar, wind, or hydroelectric power plants.
As per a National Geographic estimate, a geothermal installation takes up 404 sq. miles of land to produce 1 GWh of electricity, while a wind farm occupies 1335 sq. miles and a solar farm needs 2340 sq. miles to generate the same amount of electricity.
The comparative smaller land footprint of geothermal energy is a huge advantage as land is a premium commodity that can be put to a variety of uses including producing food for us.
4. Wide range of applications
Geothermal energy is not all about large-scale power plants alone. A geothermal heat pump can provide heat to residential and commercial buildings. For this, extreme temperatures and pressure are not necessary. In fact, this works better with low-temperature geothermal reservoirs.
Geothermal heat reservoirs of lower temperature are present everywhere across the world just below the earth’s crust. To access this, there is no need to dig as deep as in the case of geothermal power plants. As heating buildings is one of the foremost needs for electricity, a geothermal installation can meet this demand without much effort.
5. Heating and cooling
The fact that geothermal energy can heat buildings is something we already know. But the geothermal heat pumps can be used to cool the interiors of buildings as well. The heat pump absorbs the heat from inside the room and transfers it to the ground using the ground loop buried in your yard. The ground acts as a heat sink.
6. New technologies, new projects
Geothermal energy is one of the least explored alternative energy sources despite its early use. With the recent emphasis on renewable energy to bring down fossil fuel use, geothermal energy is experiencing a revival.
Newer technologies to tap the energy from the earth’s interiors are being invented. Newer locations are being identified and newer power plants are being built to harness geothermal energy. More and more applications for geothermal energy are being discovered. It is an exciting time for geothermal energy.
7. Long-lasting infrastructure
Like all power plants, a geothermal energy plant is also a high-investment venture. However, once set up, it can continue to function for a great many years without requiring more investment. The long lifespan of the geothermal power plant raises its “greenness”.
As per the US Department of Energy estimate, underground infrastructure for geothermal power plants has an expected lifespan of 50 years, while the geothermal heat pumps last for a minimum of 20 years.
Disadvantages of geothermal energy
Not at all locations on the earth’s crust can we harness geothermal energy. Though magma is present deep down the surface of the earth at all locations, the conditions are not right everywhere to tap the heat energy of the earth’s interior. This is definitely a constraint for setting up geothermal energy plants.
Geothermal power plants need reservoirs with above 100°C temperatures. These are usually found near tectonic plate borders and hot spots. Places lying along fault lines are ideal locations for geothermal power plants.
For instance, California is a perfect location as it lies close to the Ring of Fire, a belt in the Pacific Ocean well-known for its active volcanos and frequent earthquakes. However, low-temperature geothermal reservoirs are available across the country but none of them are suitable for setting up power plants.
2. High upfront cost
Setting up the underground and above-ground infrastructure to harness geothermal energy is high, higher than the initial expenditure for solar and wind farms. As per Lazard’s LCOE analysis, a geothermal power plant costs $4000-6000/kWh, while the upfront cost for a solar farm is about $1250/kWh and for a wind farm, it comes to $1550/kWh. Even for a combined-cycle gas plant that uses fossil fuels like natural gas, the investment cost is in the range of $1000-1500/kWh.
Most of the high setup cost comes from the need for drilling deep into the earth’s crust. This is one of the major deterrents for setting up new plants.
3. Can trigger earthquakes
Geothermal plants can be built only close to tectonic plate borders where there is already a high probability for earthquakes and volcanic eruptions. Drilling 1-3 km into the earth’s crust can result in disturbance of the tectonic plates, leading to earthquakes.
The drilling activity and constant pumping of hot water and steam from the earth’s interior can create instability in the region. This may trigger earthquakes. Besides this, geothermal plants can make the land slowly subside when the geothermal heat reserves in the earth’s interior get depleted.
4. Inadvertently release greenhouse gasses from the earth’s interiors
Vast quantities of greenhouse gasses are trapped inside the earth. At the time of drilling and plant operation, some of these gasses may find their way up and enter our atmosphere. Besides this, these power plants are also associated with sulfur dioxide and silica emissions. During its operation, the plants can also bring up traces of toxic heavy metals like arsenic, mercury, and boron to the surface.
5. Questions about its sustainability
When hot water and steam are constantly pumped out from the reservoirs, they may get depleted if the plants are not managed well. To overcome this constraint, the cold water is injected back into the reservoir. Geothermal energy is sustainable when managed properly.
Geothermal resources come with a lot of pluses and a few minuses, the pluses far outweighing the minuses. There is no doubt that more work needs to be done to make geothermal energy sustainable and more efficient.
More than anything else, it can help in reducing our use and dependence on fossil fuels, which is our topmost priority now and in the coming years.