In this blog post, we’ll explore the concept and characteristics of renewable energy, its main types and principles, and its potential as a future energy source.
“The Stone Age did not end because we ran out of stones.”
These are the words of Yamani, the former Saudi Arabian Minister of Petroleum. This statement applies just as well to modern energy issues. Renewable energy has been rapidly developed as an alternative energy source to prepare for the depletion of fossil fuels—such as coal and oil—which have long been the primary energy sources. However, applying this quote reveals that renewable energy holds value beyond being merely a second-best option or substitute for fossil fuels; it is not simply a matter of “using renewable energy because fossil fuels will eventually run out.” If renewable energy technologies continue to advance and become economically viable, there is a strong possibility that renewable energy will establish itself as a major energy source even before fossil fuels are completely depleted.
The “new” in “renewable energy” refers to “newly developed future energy,” while “renewable energy” refers to energy that is continuously supplied by nature and is, in effect, inexhaustible. Unlike fossil fuels, renewable energy poses very little risk of depletion and produces relatively low emissions of greenhouse gases and environmental pollutants during the power generation process. Conventional fossil fuels not only have limited reserves but also pose the problem of placing a burden on the environment as they are consumed. In contrast, renewable energy is continuously supplied by nature and is considered an important energy source for future society due to its eco-friendly characteristics.
There is a wide variety of renewable energy sources, including solar energy, wind energy, ocean energy, geothermal energy, bioenergy, waste-to-energy, small-scale hydropower, fuel cells, and hydrogen energy. The current level of commercialization varies by technology, and some energy sources face challenges related to economic viability, storage technology, and infrastructure development. For example, hydrogen energy is considered an area requiring further development in production processes as well as storage and transportation technologies. Among the various types of renewable energy, the sectors currently being utilized most actively and experiencing continuous technological advancement are solar energy, wind energy, and ocean energy. Wind and solar energy are already being utilized on a large scale in countries around the world, and ocean energy is also undergoing steady research and development as a future energy source. This article aims to take an in-depth look at these three representative forms of renewable energy: solar energy, wind energy, and ocean energy.
Solar energy utilizes the radiant energy emitted by the sun. The amount of radiant energy emitted by a massive, high-temperature celestial body like the sun is enormous, and even if only a portion of it reaches Earth, it provides a vast amount of energy. Like other forms of renewable energy, solar energy is a clean, inexhaustible resource. In particular, solar energy has the advantage of not requiring long-distance energy transmission, as it can be generated and used directly at the point of need. Furthermore, maintenance costs are relatively low, and power generation facilities have a long service life. On the other hand, a major limitation is that power generation varies significantly depending on the season, weather, and whether it is day or night.
Solar energy is broadly categorized into photovoltaic power generation and solar thermal power generation. Photovoltaic power generation is a method that uses sunlight directly to produce electrical energy. It uses solar cells to convert light energy into electrical energy, and the surface of these solar cells is made of semiconductor materials such as silicon. To briefly explain the operating principle: when light with energy above a certain threshold strikes the semiconductor surface, electrons are displaced due to the photoelectric effect, and this flow of electrons creates an electric current, thereby generating electrical energy. To increase the efficiency of solar cells, methods such as forming microstructures on the surface to reabsorb reflected light or using tracking systems that automatically adjust the panel’s orientation according to the sun’s movement are employed.
Solar thermal power generation is a method that converts light energy obtained from the sun into thermal energy, which is then used to generate electricity or for heating. The device that converts light energy into thermal energy is called a collector.
Collectors use mirrors to concentrate sunlight onto collector tubes, heating the fluid or heat transfer medium inside the tubes to generate thermal energy. The heat generated in this way is then utilized for power generation or heating after passing through heat exchangers and thermal storage systems. To improve the efficiency of solar thermal power generation, it is crucial to minimize heat loss; to this end, the development of insulation materials and high-performance collectors is ongoing.
Solar power has spread very rapidly worldwide since the 2000s and is currently used as a major power source in countries around the world, including China, Europe, and the United States. The price of solar power generation equipment has continued to decline, significantly lowering the cost per unit of electricity generated; however, economic viability varies depending on local solar radiation levels and installation conditions. Thanks to technological advancements and large-scale production, solar energy has established itself as one of the most competitive renewable energy sources today.
Wind power is currently one of the renewable energy sectors undergoing the most active research and development, alongside solar power. The greatest advantage of wind power is that it is a clean energy source available in unlimited quantities; unlike solar power, it can generate electricity at night or on cloudy days as long as there is a certain level of wind. Furthermore, maintenance is relatively easy, and the cost per unit of electricity has been steadily decreasing, leading to significantly improved economic viability. On the other hand, large-scale wind farms must address issues such as changes to the landscape, noise, bird collisions, and site selection.
First, let’s examine the basic principles of wind power generation. Natural wind, which possesses kinetic energy, rotates the rotor (a rotating component with blades attached) of a wind turbine. As the rotor rotates, the shaft connected to it also rotates, and this rotational motion is converted into mechanical energy. Inside the generator, this mechanical energy is then converted into electrical energy, producing electricity that we can use. Therefore, one of the most critical factors in wind power technology is designing a rotor that can efficiently convert the wind’s kinetic energy into mechanical energy.
To understand an efficient rotor, we first need to examine the principle by which the rotor converts energy. The cross-section of a wind turbine blade is very similar to that of an aircraft wing. In other words, the principle behind the rotation of a wind turbine rotor is the same as that behind an aircraft’s flight. Like an aircraft wing, the rotor’s blades generate lift through relative motion with the air when the wind blows, and this lift creates torque on the rotation shaft, causing the rotor to rotate. This is the core principle by which the kinetic energy of the wind is converted into mechanical energy.
So, what makes a rotor efficient? The most efficient rotor is one that can generate greater torque under the same wind conditions. To achieve this, the blades must be structured to generate sufficient lift, and the aerodynamic principles applied to aircraft wings apply here as well. The angle of attack is defined as the angle between the wing’s centerline and the relative velocity of the air, and it is a crucial factor in determining the magnitude of lift. Generally, the angle of attack that yields the highest lift is between approximately 10° and 15°. Furthermore, lift is closely related to the wing’s cross-sectional area. As the cross-sectional area increases, lift also increases; however, drag increases simultaneously, which can reduce rotational efficiency. Therefore, to design the most efficient wind turbine, it is necessary to comprehensively consider the blade’s angle of attack, cross-sectional area, and shape to achieve an aerodynamically optimized structure.
Wind power is currently regarded as one of the most cost-effective forms of renewable energy. Although the cost of power generation was somewhat higher than that of fossil fuels in the past, technological advancements, the scaling up of facilities, and improvements in operational efficiency have made it one of the cheapest methods of electricity production among new energy sources in many regions around the world. Furthermore, as wind power facilities continue to expand worldwide, their share of global electricity generation is steadily increasing. In particular, countries such as Europe, China, and the United States are actively developing not only onshore but also offshore wind power, and in some nations, wind power accounts for a significant portion of total electricity generation. These changes demonstrate that wind power has ample potential to establish itself as a major energy source of the future.
Ocean energy is a renewable energy sector that has recently been receiving increasing attention and generating high expectations. The biggest challenge facing ocean energy is that the construction and maintenance of power generation facilities require significantly higher costs compared to other renewable energy sources. Furthermore, because energy density is relatively low and facilities must be designed to withstand the marine environment, the initial investment burden is substantial. However, as technology advances and large-scale power generation facilities operate stably, ocean energy has the potential to become a major energy resource. Ocean energy is broadly categorized into tidal energy, current energy, and wave energy. Let’s examine the characteristics of each.
First, tidal energy is currently the most commercially developed form of ocean energy; it generates electricity by utilizing the difference in sea level caused by the ebb and flow of the tides. Its basic principle is similar to that of onshore hydroelectric power. Because tidal phenomena occur in a regular cycle, power generation can be predicted with relative accuracy, enabling stable electricity production. Generally, the efficiency of tidal power generation increases in areas with a larger tidal range, so it is advantageous to construct power plants in regions with such geographical conditions.
Second, tidal current energy utilizes a principle very similar to that of wind power. Just as wind rotates the rotor in wind power generation, tidal current power generation uses ocean currents flowing beneath the surface to rotate underwater turbines and produce electricity. It has the advantage of having a relatively low environmental impact and enabling stable power generation. The energy generated is closely related to the speed of the tidal current, and power generation efficiency increases in areas with faster currents. In South Korea, locations such as Uldolmok and Jangjuk Strait are recognized as prime sites for tidal power generation, and related demonstration studies and technological development are ongoing.
Third, wave power is a method of generating electricity by harnessing the kinetic energy of waves. Various devices are used to convert the up-and-down and back-and-forth movements of waves into electrical energy. However, since wave intensity and direction are not constant, technical challenges remain in achieving stable power generation. Nevertheless, if wave power technology continues to advance, it is highly likely to grow into a power generation method with significant potential among marine energy sources.
In addition to the energy sources introduced in this blog post, various other renewable energy sources—such as geothermal energy, bioenergy, small-scale hydropower, and waste-to-energy—are being researched and utilized. Currently, various renewable energy technologies are being actively developed worldwide to achieve carbon neutrality and address climate change, and energy storage systems and smart grid technologies are also advancing in tandem. Although renewable energy offers numerous advantages, it has not yet been able to completely replace all fossil fuels because challenges remain, such as fluctuations in power generation, energy storage technology, the construction of transmission grids, and economic viability. However, technology is steadily advancing, and countries around the world are continuously expanding the share of renewable energy in their energy mix. If the efficiency and economic viability of renewable energy continue to improve in the future, it is highly likely to establish itself as a core energy source for future society.
