This blog post explains the principles and potential of various renewable energy sources like solar, wind, and geothermal power in an easy-to-understand way.
With frequent extreme weather events occurring worldwide recently, interest in environmental issues is higher than ever. Particularly, coal, which has excellent thermal efficiency but causes environmental pollution due to high carbon dioxide emissions, has long been facing gradual phase-out. Consequently, research and development into renewable energy, which places significantly less burden on the environment than conventional resources, is actively underway. In Korea, various institutions such as Korea Hydro & Nuclear Power and the Korea Photovoltaic Industry Association are accelerating the development of renewable energy technologies. Beyond the familiar solar and wind energy, let’s explore what other resources fall under renewable energy, their respective characteristics, and their future potential.
While renewable energy often brings to mind only solar thermal energy, its scope is much broader than one might think. First, solar thermal energy directly utilizes the heat delivered by sunlight. This refers to using the heat itself for heating, hot water supply, cooking, etc., without undergoing a separate electrical conversion process. Examples include directly utilizing sunlight through a home’s windows for daylighting or using sunlight to heat water for hot water or heating. In countries with vast territories like the United States, methods are also employed where solar heat is concentrated over large areas to generate electricity in towers. The most critical factor to consider in solar thermal energy is ‘solar radiation’. Solar radiation is influenced by a region’s latitude, climate, and hours of sunshine. By adjusting the angle of solar collectors or photovoltaic modules, the maximum amount of solar radiation energy can be captured. Generally, it is effective to align the tilt according to the region’s latitude in spring and autumn, reduce the angle in summer, and increase it further in winter.
The use of solar energy has a very long history. A well-known example is the story of Archimedes of ancient Greece in 212 BC, who used mirrors to concentrate sunlight and set fire to Roman ships. Later, in the late 1700s, the French scientist Lavoisier used solar energy to generate temperatures exceeding 1700 degrees Celsius, which significantly advanced its practical application potential. Modern residential design also maximizes natural lighting by considering building orientation, window placement, and glass types. Efficient energy utilization is enabled through the use of thermal storage units, hot water storage tanks, and attached greenhouses.
Solar photovoltaic energy converts the light energy generated by hydrogen transforming into helium within the sun into electrical energy for use. This is primarily achieved using solar cells, collectively referred to as photovoltaic (PV) energy. Several types of solar cells exist, with silicon-based cells being the most widely used. Silicon is abundant in the Earth’s crust, making it readily available, though it requires a purity of 99.9999% or higher. High-purity monocrystalline silicon is produced using the ‘Chokralski method’. This process involves melting polycrystalline silicon, removing impurities, and slowly pulling up a silicon seed crystal to grow it into a monocrystalline form.
Monocrystalline solar cells offer high efficiency but come with high manufacturing costs. In contrast, polycrystalline silicon cells have slightly lower efficiency but benefit from reduced cutting losses and greater economic advantages. Additionally, there are gallium arsenide-based and indium phosphide-based solar cells that boast high efficiency and resistance to high temperatures and radiation. With current technology, it is difficult for monocrystalline solar cells to exceed 25% efficiency due to various loss factors (surface reflection, series resistance, excess photon energy, etc.).
Solar cells are composed of basic units called ‘cells’. A ‘module’ consists of 36 cells connected in series. Connecting multiple modules in series to increase voltage forms a ‘string’. An ‘array’ is a collection of multiple strings. When installing a solar power system, various factors must be considered, including reduced power generation due to shading, winter snowfall, heat dissipation issues, and battery lifespan. While solar power generation is highly advantageous environmentally because it does not emit pollutants during the generation process, it is important to note that energy consumption is sometimes required for high-temperature heating.
Wind energy harnesses the power of wind, evolving from ancient technologies like Dutch windmills to modern wind turbines. Wind power generation is particularly sensitive to location and time, as output varies significantly, making site conditions critically important. Wind turbines are categorized by how their blades position themselves relative to the wind direction: ‘upwind’ (front blades) and ‘downwind’ (rear blades). Upwind turbines struggle to self-align, requiring separate drive mechanisms or tail blades. Conversely, downwind turbines can naturally adjust direction, but their instability in air currents is a drawback.
Wind turbine operation methods are broadly categorized into two types: maintaining a constant tip speed ratio to enhance output efficiency, and adjusting blade rotation speed to produce electricity at a fixed frequency. Wind turbines inherently generate a certain level of noise due to their rotating drive components, but technological research, such as gearless designs, continues to address this issue.
Geothermal energy utilizes heat from the Earth’s interior, harnessing heat generated by radioactive isotope decay or heat release from the mantle. The average geothermal gradient is around 25-30 degrees Celsius per kilometer, but in regions with active geothermal development, like Pohang in South Korea, it can reach 100 degrees Celsius per kilometer. Geothermal energy is largely unaffected by weather or seasonal changes, offering the significant advantage of stable, 24-hour energy supply. The most common method involves injecting cold water underground through boreholes and extracting the heated water for heating applications. In addition to high-temperature geothermal systems and methods utilizing natural ground temperatures, research is underway on Enhanced Geothermal Systems (EGS), a deep geothermal development method. However, this technology remains costly. Furthermore, a widely used method involves installing pipes underground in buildings to utilize geothermal energy for cooling in summer and heating in winter.
When utilizing geothermal energy for power generation, systems are categorized based on the heat transfer medium used, such as dry steam, single-flash, double-flash, or dual-cycle power generation. These systems are gaining attention for their ability to provide stable energy supply without relying on conventional fossil fuels.
Bioenergy is energy derived from organic matter or byproducts originating from plants and animals, with representative examples including biodiesel, biomethane, and bioethanol. This also includes collecting gas generated from landfills for use as an energy source. Biofuels are produced through thermochemical conversion (mixing carbon monoxide and hydrogen to create other hydrocarbons) or fermentation methods (using yeast to convert sugars into ethanol). Such bioenergy is particularly gaining prominence as a practical alternative to replace transportation fuels.
Jeremy Rifkin, President of the U.S. Institute for Economic Trends, predicted in his 2014 keynote address at the Energy Grand Forum that “as renewable energy technologies advance, the marginal cost of electricity production will approach zero within the next few decades.” In his book The Zero Marginal Cost Society, he predicted that the development of the Internet of Things (IoT) would connect communications, transportation, and energy into a single network, giving rise to a new economic structure where the production costs of energy and goods would become extremely low. The cost of renewable energy generation, which reached $68 per watt in the 1970s, has now dropped to 60 cents. It appears an ‘energy sharing era’ is approaching, where anyone can directly produce energy and share surplus electricity with others.
Technological development to overcome the instability of renewable energy is also actively underway. For example, LG Chem’s Energy Storage System (ESS) is applied to LG CNS’s renewable energy power plant system, the ‘Microgrid Solution’. This allows electricity generated by solar power to be stored and supplied during peak demand periods. This shifts the traditional ‘production-consumption’ energy structure to a ‘production-storage-consumption’ model, compensating for the output fluctuations inherent in renewable energy. Particularly, as the share of renewable energy exceeds 10% of total power generation, grid instability could become problematic; ESS is recognized as a key technology to address this challenge.
To prepare for our future, we need a thorough understanding of resources like solar thermal, solar photovoltaic, wind, geothermal, and bioenergy—those with low environmental pollution concerns and high thermal efficiency potential. Renewable energy will become a crucial key, transforming not just alternative energy but the entire future social structure and economic system. How well we understand and prepare for this technology now will determine whether a cleaner, more sustainable future unfolds.
