April 25, 2021 by Lianne Frith
Given its high costs and risks, geothermal energy harnessing is far from the most popular energy solution. Nevertheless, engineers have been developing new and improved methods of tapping into our underground resources. We consider geothermal energy developments and their overall potential.
Geothermal engineers explore new ways of harnessing geothermal energy by using technology to convert thermal energy into electrical power. They use the heat that naturally radiates below the Earth’s surface, taking advantage of the constant underground temperatures, and build the processes and equipment required to extract and convert that energy.
Geothermal engineers have traditionally achieved this by either pumping cold water into geothermal reservoirs, converting water into steam at the Earth’s surface, or extracting it directly from shallow geothermal wells.
And now, by experimenting, analysing, and further developing geothermal technology and monitoring energy fields, geothermal engineers are making even more progress at finding the potential for geothermal energy.
The Nesjavellir Geothermal Power Plant in Iceland
Image credit: Pixabay
The Earth’s core is a nuclear furnace, with temperatures exceeding those of the surface of the sun. Over time, the heat migrates upwards as molten rock, or magma, carrying with it enormous heat. Put simply: the deeper you go, the hotter it gets.
In fact, even at just ten kilometres below the surface, temperatures often exceed 300 degrees centigrade—well above what geothermal plants need to generate electricity. According to the Union of Concerned Scientists, the amount of heat within about 33,000 feet of the Earth’s surface contains 50,000 times more energy than all the oil and natural gas resources in the world.
Geothermal energy offers many advantages over its renewable energy counterparts, it is available worldwide, it is relatively clean, with 24/7 availability. What’s more, a geothermal facility takes up less space than other power plants: National Geographic states that 1,046 square kilometres of land are needed to produce one gigawatt-hour (that’s 1,000,000 kilowatts for one hour) of energy. This is far less demanding than the amount of land required for facilities that offer that same amount of energy: 3,000 km2 required for wind, over 8,000 km2 for solar photovoltaic, and over 9,000 km2 for coal.
A diagram of a geothermal power plant
Image credit: Wikimedia Commons
While countries have poured billions of dollars into renewable energies, such as wind and solar, geothermal has been sidelined. However, while wind and solar appear economical, they can’t generate electricity all the time. Even combined with battery power, they struggle to supply electricity for the duration required during peak periods.
Grid operators need to find a way to ensure steady electricity. Geothermal has an opportunity to fill a critical gap in the energy transition, providing the round-the-clock supply of electrons that we need.
There are, however, some key challenges that need to be addressed first—three of which are covered next.
Geothermal energy harnessing has historically appeared to be the expensive option, costing double that of onshore wind and five times that of solar. This is on top of the initial cost of installing geothermal technology and the requirement for achieving a sophisticated infrastructure.
Plus, the subsurface exploration required for geothermal energy is one of the technology’s biggest barriers, particularly due to the complexity involved. While the Earth has virtually endless amounts of energy and heat beneath its surface, that subsurface energy is difficult to access.
The relevant areas need to not only be hot, but must also contain liquid and be permeable. For direct energy production, deep drilling into solid rock is required, so as to intercept natural fractures to inject water and create wells. While this form of energy production is constant and efficient, it’s, again, technically complex. Many aspects need to come together simultaneously to create the right environment.
Injecting high-pressure streams of water deep into the Earth can induce seismicity and may even cause earthquakes (while rare, such a risk is nevertheless extremely serious). On top of this, controlling and monitoring seismicity underground is yet another complicated undertaking: for instance, geothermal plants have been linked to subsidence, which can result in damage to pipelines, roadways, buildings, and natural drainage systems.
An infographic that covers oil, gas, and geothermal drilling (particularly in relation to how deep each one occurs underground)
Image credit: Department of Energy and Climate Change via Flickr
Recent developments have found ways to leverage the Earth’s heat where natural pockets of accessible hot water and steam don’t exist or are difficult to access. Enhanced geothermal systems use drilling, fracturing, and injection to give hot-but-dry underground rock the fluidity and permeability it needs to generate electricity.
Ranging from one to 4.5 kilometres deep, injection wells are created by pumping high-pressure cold water to force the rock to create new fractures and form a reservoir of underground fluid. Some projects that are taking enhanced geothermal systems a step further include the following.
The FORGE (Frontier Observatory for Research in Geothermal Energy) project in Utah is running a study and test site for enhanced geothermal energy. The project kicked off in 2020 by drilling a highly deviated well into hard, hot crystalline granite. These wells are frequently drilled for oil and gas production, but this is the first time that it has been attempted for geothermal energy production.
Once the well is completed, a series of tests will be run to determine the stress conditions while ensuring careful microseismic monitoring. The project could be vital in proving that enhanced geothermal energy technology is commercially viable.
One of the first U.S. geothermal power plants in almost a decade, the Hell’s Kitchen Lithium and Power Project is due to start operating in 2023. The project aims to combine the extraction of lithium with geothermal power generation on a site at the Salton Sea in California.
A research group from KAUST University in Saudi Arabia is also looking into how to improve efficiency and reduce the operating pressure of enhanced geothermal energy systems. The team plans to enhance the flow heat exchange capacity of the system with the use of horizontal drilling, hydraulic fracturing in the injection well, and the production of a well drilled into the fracture zone.
A hole drilling rig for a geothermal plant—a complex undertaking
Image credit: Pixabay
IRENA (the International Renewable Energy Agency) has predicted that the output of geothermal energy in Europe could increase eight-fold by 2050. There is clearly an enormous untapped potential and the new advances that we’re seeing could help many countries to overcome the technical and financial barriers that have been standing in their way.
Nevertheless, the industry will still need to see a leap in the scale and quantity of projects such as FORGE if it will be able to sufficiently build on technological developments and demonstrate that costs can become economically viable. Only then could geothermal power truly become a key component in the world’s green-energy future.
