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| Fig. 1: Floating element of the Powerbuoy. (Source: Wikimedia Commons) |
South Korea has been growing rapidly over the last 30 years, which has lead to massive energy consumption. In addition, South Korea relies on their imports for most of its energy sources like petroleum and coal. [1] This limited supply of energy along with its strong demand for it creates many issues if there isnt any significant innovative domestic energy production. As a result, South Korea decided to turn towards their peninsula coast to generate renewable offshore wave energy.
The Korean Peninsula is surrounded by the Yellow Sea, East China Sea, and East Sea, and tide heights ranging from 4 to 8 meters on the side of the Yellow Sea. [1] The variability is partially dependent upon wind speeds and also many other external factors. Seasons also play into producing optimal tidal energy, as winter is the best season for Korea to harvest energy. On the south-western area of the Korean Peninsula in the winter, wave energy is relatively large and reaches up to 25 kW/m due to seasonal monsoon patterns. On the other hand, the summer season provides the least amount of wave power on average because of its associate anticyclone period, which doesnt produce high waves. To calculate offshore wave power, the following equation is used: [2]
| P | = | ρ g2 T H2 32 π |
where P is wave power per meter of target area, ρ represents seawater density, g is the gravitational acceleration, T is the energy period and H is the significant wave height. [2] The height of the waves from the Yellow Sea and the East China Sea on average can vary from 1.49m to 1.7m depending on the variability of latitude in the region. [3] The average range for saltwater density is from 1020-1030 kg/m3, while the wave energy period can vary from 1.8 to 7.2 seconds. [4]
Although South Korea is still developing new pilot tests, many of the projects to effectively capture wave energy have the foundation of utilizing buoys in their new methods. One renewal energy proposal regards a wave energy- harvesting device that contains multiple rows of buoyance columns connected to flexible platforms. The platforms are associated with couplings of multiple buoyance columns through the use of linear connectors. Then, a mechanism that works as a linear hydraulic generator power take off (PTO) is implemented between each platform and column to capture the energy of the oscillating waves. [5]
Still, the most promising form of wave energy harvesting is a device created by an American company called Powerbuoy (see Fig. 1). It is a disk shaped buoy that works against a submerged cylindrical piece. At the bottom of the cylinder is a damper plate that increases inertia from the added surrounding water mass. The bobbing between the floating element and the cylindrical counterpart is converted into electricity through a hydraulic PTO. In 2008, there has been a 40 kW prototype without grid connection deployed in Spain, but the founders plan to create a wave harvesting farm with 9 buoys, each at 150 kW. [6] According to the BP Statistical Review of World Energy, South Korea's electric power consumption in 2016 was 552.1 TWh. [7] The average power consumption was thus
Thus the fraction of South Korea's total power needs that nine 150 kW buoys could provide is
which is only 0.0022%. As a result, there is a lot of speculation in the effectiveness of this device since each device is estimated to cost around $64 million.
Although the new proposal is still being refined and developed, there are also many concerns about wave energy harvesting. Some of the challenges include the ability to harvest the energy from multidirectional waves and the viability in Korea's subnormal wave conditions, especially since the nature of wave energy harvesting is difficult when trying to harvest slow, random, and high force oscillatory motion and trying to make use of this force to drive a generator capable of producing acceptable output. However, the one concern that Korea does not have to worry about is if the device is able to withstand extreme wave conditions, since the waves experienced around the country are not significant. [8] Although South Korea is publicly trying to develop new wave solutions to their energy dilemma, they will still likely turn to nuclear energy in secrecy, since much more energy can be produced through such a method. It will be interesting in the next couple of years to see how South Korea will deal with its energy issue, as most of its energy resources have been depleted.
© Jesse Kuet. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] G. Kim et al., "An Overview of Ocean Renewable Energy Resources in Korea," Renew. Sust. Energy Rev. 16, 2278 (2012).
[2] E. Bonifacio, "Wave Energy," Physics 240. Stanford University, Fall 2010.
[3] Hwang, Paul A., et al., "Winds and Waves in the Yellow and East China Seas: A Comparison of Spaceborne Altimeter Measurements and Model Results," J. Oceanogr. 55, 307 (1999).
[4] A. M. Muzathik et al., "Ocean Wave Measurement and Wave Climate Prediction of Peninsular Malaysia," J. Physical Sci. 22, 77 (2011).
[5] H.-C. Zhang et al., "A Floating Platform with Embedded Wave Energy Harvesting Arrays in Regular and Irregular Seas," Energies 10, 1348 (2017).
[6] A. F. de O. Falcão, "Wave Energy Utilization: A Review of the Technologies," Renew. Sustain. Energy Rev. 14, 899 (2010).
[7] "BP Statistical Review of World Energy 2017," British Petroleum, June 2017.
[8] B. Drew, A. R. Plummer, and M. N. Sahinkaya, "A Review of Wave Energy Converter Technology," Proc. Inst. Mech. Eng. A 223, 887 (2009).
