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The ocean is a huge treasure house of energy. In theory, the ocean can fully meet all the energy needs of the earth and will not cause any pollution to the atmosphere. Therefore, ocean energy is also known as “blue energyâ€. Compared with wind energy or solar energy, blue energy has geographical distribution advantages. The ocean covers 75% of the earth's surface, and about 44% of the world's population lives within 150 kilometers from the coastline. However, compared with renewable energy sources such as wind power and solar energy, development of blue energy sources and energy harvesting have always been fraught with difficulties. The main reason is that traditional electromagnetic generators are based on Faraday's law of electromagnetic induction, and their output power and frequency squared. In proportion, a stable and very high working frequency (50~60Hz) is required to obtain a stable output, but the wave frequency, tidal current, and ocean current in the ocean are relatively low (0.1~5Hz). And the waves are fickle and the movement is irregular. It is difficult to use an electromagnetic generator to collect energy. In contrast, the triboelectric nanogenerator proposed by Wang Zhonglin, chief scientist of the Beijing Institute of Nano Energy and Systems, Chinese Academy of Sciences and director of the Georgia Institute of Technology in 2012, has an output current proportional to the mechanical energy frequency over a wide frequency range. While the output voltage remains relatively stable, for wave frequencies below 5Hz, the output efficiency of the friction nanogenerator is much higher than that of the electromagnetic generator, which is very suitable for collecting blue energy.
In response to the above problems, under the guidance of Wang Zhonglin, a team consisting of Jin Yunlong, Guo Hengyu, and Wen Zhen developed a composite system based on friction nano-generators and electromagnetic generators to collect blue energy, and recently Published in Adv. Energy Mater. and ACS Nano. First, the team used the attractive force between the magnets as non-contact traction force to waterproof the friction nano-generator package, while embedding copper coils between the magnets to form a simple electromagnetic generator. The composite system can collect ocean waves and ocean currents, etc. Movement energy, and can make its output through the circuit control, make its impedance match, as shown in Fig. (a). Subsequently, based on the same principle, the team designed a concentric cylindrical device structure that can not only work underwater, but also collect ocean wave vibration and ocean current energy, as shown in Figure (b). It is worth noting that because the friction nanogenerator can work stably under low frequency conditions, the device can collect blue energy at any moment. When the frequency of ocean motion is faster, the electromagnetic generator can provide its own in addition to non-contact traction. Power is output so that the device can continue to operate over a very wide frequency range, collecting blue energy at any frequency.
The study proposed a practical and feasible solution for the application of friction nano-generators in the field of blue energy. It has achieved the functions that cannot be achieved by traditional technologies, and will also be a subversion of the power generation technology in the past 100 years.
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