In this blog post, we’ll explore the principles and applications of geothermal energy, its current use around the world and in South Korea, and its future potential.
The Earth may look cold on the surface, but its interior is warm
The blue image of the Earth’s surface naturally brings to mind a sense of coldness. But what about the Earth’s interior? Although the Earth—where oceans cover more than 70% of the surface—appears cold and calm on the outside, its interior contains vast amounts of thermal energy, including magma. This heat does more than simply keep the Earth’s interior warm; it is also a vital energy source that can be used to generate electricity, provide heating and cooling, and supply hot water.
Geothermal energy is a general term for the thermal energy possessed by the Earth, and it generally refers to the heat within the Earth that humans can harness. Geothermal energy is generated by two main sources. The first is the thermal energy produced by the radioactive decay of isotopes that make up the crust and mantle. According to current research, a significant portion of the Earth’s internal heat originates from this radioactive decay process. The second is residual heat left over from the Earth’s gradual cooling process over a long period since its formation. This heat is primarily stored within the Earth and is transferred to the crust through mantle convection.
Two Methods of Utilizing Geothermal Energy
Geothermal energy can be utilized in two main ways. The first is geothermal power generation through indirect use. This method does not use geothermal heat directly but rather harnesses it to generate electricity. The most common method is the flash steam process. In this process, high-temperature water under high pressure is brought to the surface, where the pressure is rapidly reduced to generate steam; this steam then drives a turbine to produce electricity. Generally, geothermal water with a temperature of 180°C or higher is used.
Geothermal power generation offers the advantages of relatively low generation costs, relatively simple operating technology, and very low emissions of greenhouse gases and air pollutants during the power generation process. On the other hand, its disadvantages include limited applicability—as it is primarily economically viable in regions with high-temperature geothermal resources—and the need for ongoing monitoring to address ground subsidence and changes in the subsurface environment.
When high-temperature, high-pressure water is subjected to a rapid drop in pressure, it undergoes a phase change into steam. The steam generated during this process acquires high kinetic energy as it passes through a nozzle connected to a turbine, causing the turbine to rotate. The turbine’s rotational motion is then converted into electrical energy by a generator to produce electricity.
The second method is “Direct Use,” which directly utilizes underground thermal energy. Since direct use does not require extremely high temperatures like geothermal power generation, it faces relatively fewer regional constraints. It is utilized in various fields, such as greenhouses, aquaculture, building heating and cooling, and hot springs, with geothermal heat pumps being a prime example.
Recently, many buildings have been utilizing geothermal heat pumps for their heating and cooling systems. This system takes advantage of the fact that the temperature underground, at depths ranging from tens to hundreds of meters, remains relatively constant throughout the year. In the summer, heat from inside the building is released into the ground, and geothermal energy at a relatively low temperature is used to cool the interior. Conversely, in the winter, heat is drawn from the ground for heating.
Geothermal heat pump systems are highly energy-efficient, reduce refrigerant consumption, and are relatively easy to maintain. Additionally, since they can handle both heating and cooling with a single system, they offer excellent long-term cost-effectiveness. However, the higher initial installation cost compared to conventional heating and cooling systems is a factor that must be considered.
A heat pump is a device that utilizes a refrigeration cycle in which a refrigerant absorbs heat from its surroundings as it evaporates in the evaporator and then releases that heat as it condenses back into a liquid in the condenser. Because it transfers heat from a relatively low-temperature area to a higher-temperature area, it is also called a “heat pump.”
Current Status and Outlook for Geothermal Energy Utilization in the World and South Korea
The industrial use of geothermal energy began in earnest in 1904 with the world’s first geothermal power generation in Larderello, Italy. Since then, the technology has spread to Beppu in Japan, The Geysers in the United States, and Wairakei in New Zealand; today, geothermal power plants are in operation in various countries, including the United States, Indonesia, the Philippines, Turkey, New Zealand, Kenya, and Iceland.
Global geothermal power generation capacity continues to grow, with new power plants being actively constructed, particularly in Indonesia and Turkey. Furthermore, while development was previously concentrated in volcanic regions, the range of viable locations is gradually expanding as technologies for utilizing low-temperature geothermal resources and deep geothermal energy advance.
South Korea is also actively utilizing geothermal energy. However, the focus is primarily on the adoption of geothermal heat pumps for building heating and cooling rather than power generation. In the past, a deep geothermal power demonstration project was carried out in Pohang, but it was suspended after concerns were raised regarding a possible link to subsequent earthquakes. Since then, South Korea’s geothermal policy has placed greater emphasis on the adoption of geothermal heating and cooling systems—whose safety has been verified—rather than power generation.
Meanwhile, with the continuous advancement of binary cycle power generation technology—which enables power generation even from low-temperature geothermal sources—and Enhanced Geothermal Systems (EGS) technology, the potential for geothermal power generation is expanding even in regions outside volcanic areas. At Chena Hot Springs in Alaska, United States, binary power generation utilizing low-temperature hot spring water at approximately 70–80°C has been commercialized and is currently in operation; this technology is expected to further expand the scope of geothermal power generation in the future.
Consequently, active research is underway to harness geothermal resources through new engineering technologies, even in areas that were previously considered uneconomical. South Korea is also continuing research and development in various fields, including geothermal heating and cooling technologies and deep geothermal technologies. The importance of geothermal energy as a renewable energy source capable of simultaneously achieving carbon neutrality and energy security is expected to grow even further in the future.
