Chinese researchers say ships can become moving wave energy converters, using "undulation oscillators" to harvest energy from the heaving, rolling and pitching motion of ships as they move through the sea, while also acting as motion dampers to improve safety.
There are countless floating wave energy generators currently under development, but not many are used on ships, which spend most of their working time in waves. And energy storage on ships is becoming one of the most difficult obstacles to overcome in the decarbonization process. Where better to generate electricity than on ships?
Researchers at the Shanghai Institute of Ship Transport Science have proposed a twin-body point absorber system that would be installed below the cargo ship's deck to protect the cargo space while also being isolated from seawater by the hull.
The device consists of a frame, the top and bottom of which are firmly fixed to the boat, with an oscillator body on the rails that can move up and down, a spring for suspending the oscillator, and a hydraulic cylinder connected to the floor and the bottom of the oscillator.
As the oscillator slides up and down relative to the boat and fixed frame, the hydraulic cylinder pumps oil through the hydraulic power take-off to create energy. Meanwhile, the oscillator is filled with water, but has a system that adds and subtracts water to change its weight. This is especially convenient in extreme weather, when the weight of the oscillator can be reduced, thereby reducing stress on the hull structure.
The design allows the oscillator to "move along a sliding rod as the ship undergoes heave, roll or pitch motion" - thus generating energy from three different axes of motion, whereas previous designs could only generate energy from one or two axes of motion, the researchers said.
The research team built a system model for simulation testing and conducted a series of tests to determine the system's performance under different speeds, wave angles, etc. Research results show that the energy capture efficiency is highest in the wave sea, where the waves roll at 90 degrees and directly impact the ship's side. In this case, the system "can reach 90.71% of the theoretical maximum absorbed power of the axis-symmetric point absorber within a certain wave period."
The research team told RechargeNews that they are planning to next prototype the system for wave box testing and that the same system is "easily scalable" to other offshore structures.
One question the study did not investigate was how much power the system could deliver on average at a time - this, along with space considerations, will be key to whether such systems can be widely adopted.
The research has been published publicly in the journal Renewable Energy.