The need for renewable energy has been highlighted by the two oil peaks and global warming, and various forms of renewable energy, such as solar, ocean, and geothermal energy, have gained prominence. They are inexhaustible and environmentally friendly, and countries are accelerating the development of renewable energy to reduce carbon emissions and gain economic benefits.
The two oil waves of 1974 and 1978 were a reminder of the global impact that energy-producing countries can have on the world, but they also made us realize how dependent we are on fossil fuels. These events led non-oil-producing countries, which suffered significant economic losses, to become interested in developing renewable energy technologies to reduce their dependence on oil imports. In addition, global warming, which was first officially recognized in the 1972 Rome Club report, and the subsequent identification of carbon dioxide as the main culprit of global warming, increased the need for renewable energy as an environmentally friendly energy source.
With the remaining fossil fuel reserves lasting only about 40 years, and nuclear energy, which has been prominent as an alternative energy source, being unreliable due to several nuclear power plant explosions, the infinite and stable nature of renewable energy was considered to be a major advantage over conventional energy. In addition, since the Kyoto Protocol came into effect in 1997, about 32 countries around the world have implemented a carbon emissions trading system that allows them to buy and sell carbon emission rights to each other, and in May 2012, a bill for a carbon emissions trading system was passed by the National Assembly in Korea, which is expected to promote the development of renewable energy as a business that will bring economic benefits beyond just environmental protection and alternative energy development.
In Korea, renewable energy is defined in Article 2 of the “Act on Promotion of New Energy and Renewable Energy Development and Utilization” as ‘energy that is utilized by converting and using existing fossil fuels or by converting and using renewable energy including sunlight, water, geothermal, precipitation, biological, organisms, etc. and refers to 11 fields such as solar, bio, wind, hydropower, fuel cell, coal liquefaction, gasification and heavy residue gasification, marine, waste, geothermal, hydrogen, etc.’ Renewable energy is also called new energy, renewable energy, green energy, alternative energy, etc. depending on the country, and the classification method is slightly different. For example, Korea separates bioenergy and waste energy, while the U.S. combines them and refers to them as biomass.
According to a survey by the Korea Energy Management Corporation, waste energy is the most used renewable energy in Korea (67.5%), followed by hydropower (12.73%) and bioenergy (12.7%). In the United States, biomass (including waste energy) accounted for 53%, followed by small hydro (31%) and wind (11%). Globally, bioenergy (or waste energy) and hydropower are the most widespread renewable energy sources, and the types of energy used vary depending on the location and geography of each country. Renewable energy is classified according to the type of energy source directly used, and in this article, we will look at the definition of each type of energy, how it is used, and its advantages and disadvantages according to Korea’s renewable energy classification.
Solar energy is divided into solar thermal energy and solar photovoltaic energy. Solar thermal energy is used to generate power by using the collected sun’s heat to generate solar water heaters or steam. Photovoltaic energy uses the photoelectric effect of solar cells to generate electricity. Solar energy has the disadvantage that it is only available for a limited number of hours per day and is subject to weather and seasonal variations, but it has the advantage that it is pollution-free, inexhaustible, and the absolute amount of solar energy reaching the Earth’s surface is ten thousand times greater than the energy used on Earth.
Ocean energy is electricity or heat generated by converting the ocean’s tides, waves, currents, and temperature differences. Tidal energy involves submerging an underwater windmill turbine in the current and using water power to turn the turbine during high and low tides. Wave energy utilizes a piston attached to a buoy that reciprocates with the up and down motion of the waves to turn a generator. However, it is difficult to avoid environmental pollution problems because it must be generated directly in the marine environment.
Geothermal energy refers to the thermal energy of the ground, which contains high-temperature water and rocks, that comes out through the surface. Currently, geothermal energy is mainly harnessed directly from the ground, but turbines are also being researched to draw up hot water from the ground and evaporate fluids with low boiling points. Geothermal energy has unlimited potential because about 47% of the sun’s heat is stored as geothermal energy in the earth’s crust, which is recycled underground through the decay of radioactive isotopes.
Wind energy harnesses the kinetic energy of air movement and converts it into mechanical energy by spinning windmills, which in turn converts it into electricity. Disadvantages include the unpredictability of the wind and the fact that wind turbines spoil the aesthetics of the natural environment, but for large-scale complexes, the unit cost of electricity generation is relatively low, making it possible to commercialize. In Korea, wind energy is being studied with a lot of interest due to the large area of mountainous and coastal regions.
Hydropower is a small-scale, technologically simple hydropower generation that uses the same principle as large-scale hydropower, but is in harmony with local conditions. The water’s potential energy is converted into kinetic energy, and the power of the water is used to turn a turbine to generate electricity. However, disadvantages include environmental damage caused by dam construction, high initial construction costs, and fluctuations in power generation depending on precipitation.
The next option is to obtain energy, mainly in the form of fuels, by decomposing or synthesizing organic or inorganic materials. Energy produced in the form of fuel is easy to store and transport, making it highly utilizable.
Bioenergy refers to liquid, gas, solid fuels, or electrical and thermal energy derived from the decomposition of biomass. While bioenergy has the advantage of easy storage and transportation, the biomass used as feedstock must be grown and harvested, and the consumption of food as fuel can cause food prices to skyrocket. Alternatives include research into enzymes that break down organic matter, such as cellulose, and algae.
Waste to energy refers to liquid or gaseous fuels produced from the decomposition of waste, or waste heat from the combustion of waste. Waste energy can solve the problem of waste disposal, but it has the disadvantage of producing environmental pollutants during the incineration process.
Coal-to-energy is energy generated by turning low-grade raw materials into synthetic gas using coal gasification technology to drive turbines. Coal gasification and gas refining are the key processes.
Hydrogen energy is obtained by decomposing water or organic matter, and has the advantage of emitting almost no environmental pollutants during combustion. If technology is developed to store hydrogen, it can be easily transported as a gas or liquid, making it as convenient as traditional fossil fuels.
A fuel cell is an energy converter that converts the chemical energy of fuel into electricity through an electrochemical reaction. Fuel cells have the advantage of being emission-free because they do not undergo combustion, but they lack the durability and affordability to be commercially viable.
Taken together, each form of renewable energy has its own advantages and disadvantages, but the common goal is to reduce environmental pollution by using sustainable energy and minimizing carbon emissions. Renewable energy currently accounts for about 12% of global electricity production, and the UK and Germany are targeting to generate about 30% of their energy from renewable sources by 2030. Korea has also set a goal of generating about 20% of its energy from renewable sources by 2030. With these global efforts, the research field and industrial market for renewable energy is expected to grow in size and importance over time.
