AquaHarmonics, one of the teams competing for the Wave Energy Prize challenge, is developing a point absorber wave energy device consisting of power take-off (PTO) system mounted in a cylinder shaped hull with a single mooring line that has a power cable at its core.
The PTO system consists of a sheave fixed to a shaft mounted in bearings within a sealed compartment and directly coupled to a pair of axial flux generators.
The device only generates power on the rise of the wave, and during the fall of the wave the generators are operated as motors to reel in the mooring line for the next wave cycle.
During reel in, the control system of the device can provide additional energy input to achieve phase locking with any wave frequency, and according to Wave Energy Prize, this control method known as ‘de-clutching’, has been shown to effectively increase the operational bandwidth of a wave energy device.
The generated power is greater than that consumed during the wave cycle with some energy stored on board for periods of low wave activity.
The power is conditioned onboard and sent to shore via a slipring on the shaft connected to the power cable located at the core of the mooring line.
Take a look at the video of AquaHarmonics’ 1:50 scaled wave energy device under tests at the University of Michigan’s Marine Hydrodynamic Laboratory.