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Dual Purpose Vessel for Wave-Activated Power Generation and Energy Transportation  

Main Points: As a means of transmitting electric power without using submarine electric cables, the following two methods are being studied: large batteries brought by ship, and the transportation of tanks filled with hydrogen produced from water by electrolysis. However, neither of these methods has been used in actual application yet, mainly due to cost. As an alternative, the following method can be applied: electric power is stored as gravitational potential energy by winching up a weight suspended over a marine vessel, and this potential energy is reconverted into electric power by dropping the weight at distant power generation locations to rotate a power generator. Since this method allows electric power to be produced on demand, it offers a more effective means of generation.
Use of a plate weight in this type of carrying vessel will increase both the gravitational force exerted on the vessel and the resistance of water and allow the vessel to experience almost no rolling caused by waves, thereby making it possible to perform wave-activated power generation. In other words, the structure provides not only a safe, inexpensive energy transmission function, but also a wave-activated power generation function.

Outline of


The apparatus is equipped with a pontoon, which can rise and fall depending on wave motion in a seawater intake tank installed in a large marine vessel. A pinion fixed on a wall of the seawater intake tank is in contact with plate teeth on a side wall of the pontoon. The shaft of the pinion, which is connected to the shaft of a wave-activated power generator via a gear wheel, rotates the generator to generate electric power. Subsequently, the generated power is used to operate a motor to rotate a winch shaft and lift up wires connected to a plate weight. The generated power is thereby stored as the gravitational potential energy of the raised plate weight.
The winch shaft is locked by a one-way clutch so that the plate weight will not descend. When the potential energy needs to be converted into electric power, the clutch is released, and the plate weight will drop longitudinally so as to reduce the resistance of water exerted on the weight. Using this method, electric power will be generated by rotating the shaft of the generator via the power generation gear wheel connected to the winch shaft. In this manner, the potential energy that the plate weight has obtained from wave power can be converted into electric energy.
To store the potential energy of the plate weight converted from electric power obtained from external sources, such as wind power generation and photovoltaic generation, the power generation gear wheel is rotated to winch up the plate weight using a motor.
This type of marine vessel navigates to accumulate energy at sea when the sea is calm; it returns to a deep-water port near facilities with power transmission cables, such as an ocean current power generation base, and generates electric power to transmit it. In addition, an energy collection vessel can be used in the following manner. The energy collection vessel navigates to and stays in a sea area deep enough to allow the potential energy of the plate weight to be stored sufficiently. When the sea is calm, power generation vessels may be linked to the energy collection vessel with power transmission cables and transmit generated electric power to the energy collection vessel. Subsequently, the power generation vessels return to their power generation locations to generate power again. When the sea is calm at the power generation locations, the power generation vessels can be moored; in this case, they can generate and transmit electric power directly without operating their own weights.


 patent (特許第5081331号)


The following estimates are for a 200-m-long vessel, in which a 100,000-ton plate weight is suspended. The vessel can be moored at a power generation location with a water depth of 500 m, where power transmission cables are available. When waves are low, the vessel navigates to a nearby high-wave area by sailing using the electric power of its batteries previously stored by wind-activated power generation; thereby, it can perform wave-activated power generation at an average wave height of 3 m without consuming fuel.
The vessel is equipped with four pontoons 30 m in length and width and 15 m in height, and each of them weighs 1,800 t; accordingly, the lower parts of the pontoons sink 2 m into the sea under waveless conditions. When a 3-m-high wave approaches the vessel, the pontoons sink to 5 m, and the buoyancy exerted on each pontoon is calculated as (30 × 30 × 5) t - 1,800 t = 2,700 t. The buoyancy decreases as the pontoons float up, so that a buoyancy of 1,350 t is exerted on each pontoon on average. After the pontoons have been raised by 3 m, if the sea surface drops by 3 m, the position of the pontoons will be at 1 m above the sea surface; while they are left in the air, a gravitational force of 1,800 t will be exerted on each pontoon. Since the buoyancy gradually increases until the pontoons sink back 2 m into the sea after they have reached the sea surface, a gravitational force of 900 t will be exerted on each pontoon on average.
Accordingly, the energy that each pontoon obtains from a wave cycle can be calculated by E = mhg as follows:
E = (1,350 × 3 + 1,800 × 1 + 900 × 2) × 9.8 (gravitational acceleration) = 74,970 kJ.
Since the period of a 3-m-high wave is generally thought to be 8 seconds, the output per second is 7,650 ÷ 8 = 9,371.25 kW; accordingly, the output of the four pontoons is calculated as 37,485 kW in total. However, actual operation will produce losses due to the resistance of water acting on the plate weights and mechanical losses. Therefore, on the assumption of a generating efficiency of 50%, the generating capacity will become 18,742.5 kW.
Electric power generation per day calculated from this value is 449,820 kWh. On the assumption that losses due to maintenance and losses produced during generating operation will be 50 days/year, an annual profit of 3.46 billion yen will be gained at a purchasing price of 23 yen/kWh. This estimate shows that when the annual maintenance costs of the vessel including personnel expenses required for the crew and charges for usage of power transmission cables are 200 million yen with its depreciable life being five years, the vessel will make profit at a construction cost of 16.3 billion yen or less.

  Patent : Japanese patent No.5081331

  If you require more details, please contact us using the information below:

 Makoto Yasukagawa, Director of Morito Senai Hospital
 8-13 Hitokita-nishi, Moniwa, Taihaku Ward, Sendai City, Miyagi Prefecture
E-MAIL  rijityou@midorijuji.or.jp


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Renewable Energy Patents for Sale Makoto Yasukagawa.
8-13 Hitokita-nishi, Moniwa, Taihaku Ward, Sendai City, Miyagi Prefecture,〒982-0263,JAPAN
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