By Jyunichi Taki, Science Editorial Staff, Nikkei Newspaper Electric Edition
Based on some completely new ideas, Professor Tsumoru Shintake from Okinawa Institute of Science and Technology Graduate School has been tackling on practical use of wave energy generation. Utilizing smashed-up waves on coral reefs is quite an idea technologically, which is unique to Okinawa. The demonstration turbine was recently completed and now the turbines are to be implemented on a real shore.
Wave generation Is Difficult for practical use: Continuous failures worldwide
Existing wave energy on the earth is limitless and thus, there have been various proposals and trials of wave generation systems in many coastal areas worldwide. As part of global warming countermeasures, European nations are particularly active in this field, such as UK or Spain that are facing the Atlantic Ocean.
However, due to difficulties to achieve economical and durability that can resist wave shocks, the technology has been hard to be implemented its practical use. For example, “Pelamis,” which had been expected to become the first global commercialized wave generation system by a UK company, Pelamis Wave Power, Co. Ltd., started its test operation off the coast of Portugal in 2008. However, the project was stalled only after several weeks due to technical troubles, in which using bent force by waves on Pelamis’ snake-like long floating body failed in the end.
The idea by Professor Shintake uses the wave strength after “reef breaks” take place where big waves get smashed up on coral and rock reefs. Even when big waves get rolled on toward a coast, area inside coral reefs is relatively calm. Waves that roll over coral reef do not change their shapes much and get propagated for a long distance, which is ideal for surfing. According to Professor Shintake, this kind of wave is similar to so-called “soliton” in physics. Professor Shintake’s original research is on electron microscope, etc., but for the past few years, he has been focusing on energy related technologies.
Wave energy, 100 times larger than wind, can generate electricity in small scale
There are at least two advantages in waves after reef breaks. First, the velocity of the wave is rather fast, 5 or 6 m/s. Secondly, there is almost no withdrawing waves after reef breaks and it travels only to one direction, which gives more stable energy compared to waves off the coast.
The demonstration machine with 35-cm diameter propellers completed on top of rock reefs in October 2017 are now exposed to rolling waves. High performance neodymium magnet used for the generator and water-proof structure around the axis are incorporated in its design to prevent the generator’s breakage due to extra forces applied.
Professor Shintake’s idea is to generate electricity with a number of these machines on the reef breaking coast. “For wind turbine, we need gigantic blades, but the energy density of wave is more than 100 times larger than that of wind, and it can generate sufficient electricity even in small sized generators.”
If the expected performance is achieved through demonstration tests on the coast of Okinawa, Professor Shintake plans to go into a mass production phase in 2018, aiming for the next phase experiment close to practical use. Since the size of this wave turbine is small, installation cost is low, bringing down the entire cost along with the efficiency of mass production. If they succeed in bringing down the cost less than a light automobile (one million to two million yen), the electric generation cost would be five to 10 yen per kW/h, which is advantageous over thermal or nuclear energy.
European ocean energy generation predicted to be equivalent to 150 nuclear reactors in 2050
Installation area of wave turbines is not limited on coral reefs. The most coastline of Japanese archipelago is covered with tetra pots that break waves to protect the coastal areas. Professor Shintake explains, “If we relocate the existing tetra pots slightly off the coast to make them as artificial rock reefs, and generate electricity with waves that roll over the rock reefs, we can improve the scenery of the coastal line and also generate electricity. This should be so-called killing two birds with one stone.”
Relocating the tetra pots will require a large scale public construction, and there should be some areas where such construction work would not be possible. Rather, there would be more needs and expectations from Pacific island nations, which would welcome such usage of oceanic energy sources rather than building thermal power plants that emit CO2.
As for wave power generation in Japan, a demonstration test conducted by New Energy and Industrial Technology Development Organization (NEDO) in Sakata Port, Akita prefecture is already well known. The generator is called, “Air Turbine-type Wave Power Generation System,” which utilizes air flows generated by vertical fluctuation of ocean surface to rotate a turbine. The generator is not going to be installed on the surface of water in a floating state, but to be installed on the coast in a fixed state. In 2015, the generator reached the maximum of 13 kilowatt, having completed the demonstration test as a success.
The EU Oceanic Energy Association announced a prediction that 3.6 million kilowatt oceanic energy sources will be introduced in 2020, which would jump to almost 200 million kilowatt in 2050, equivalent to 150 nuclear reactors of 1.3 million kilowatt scale, covering approximately 15% of total electricity demands of 27 EU nations. Oceanic energy generation is regarded as one of the core renewable energy source, following solar and wind power.