Inspired by the mechanics of the human heart, a new type of wave energy conversion system developed in Sweden is now bobbing in the waves off Orkney, Scotland. It’s undergoing evaluation for survivability, loads and performance in off-grid operations, in order to validate the business case for full-scale implementation in target markets.
Developed by Swedish startup CorPower Ocean AB, the C3 wave energy converter system is based on research in machine design at KTH Royal Institute of Technology in Stockholm, as well as control technology at NTNU in Trondheim.
The waters near Orkney are said to provide some of the world’s best tidal and wave energy sources, and the region has become a hotbed of renewable energy experimentation.
“We are seeing immense value in working in the Scottish ocean energy ecosystem, where we can benefit from lessons learned from previous wave projects,” Möller says. “Working closely with the Orkney supply chain provides us with unique operational experience to the project, as they have deployed more ocean energy devices than anywhere else in the world.”
Known in the wave energy industry as a point absorber type system, the C3 consists of a buoy that absorbs energy from the waves, plus a drivetrain that converts the buoy motion into electricity. The unit is based on patents by Swedish cardiologist Stig Lundbäck, some of which are inspired by his research into heart pumping and control functions.
To convert the linear motion of the buoy into an energy-generating rotational motion, the system relies on a special rack and pinion gearbox developed at KTH. In concept, it works like a rack and pinion steering system. Rotate a car’s steering wheel and at the end of the steering column is a pinion, or cogwheel, which meshes with a rack aligned with the axle. Turning the wheel then moves the axle in a horizontal motion, from side to side.
In the CorPower wave conversion system, the rack is pushed up and down by the buoy bobbing on the waves. This action then moves eight small gear wheels along the rack. The secret to the cascade gear design is how the pinions and the gears work together along with flexing units. Eight pinions share the force from the rack, which is evenly distributed with the help of a patented system that “ensures extreme levels or robustness required in the harsh operational environment,” Möller says. The system then can handle high forces and high velocities at the same time. The high velocity is transferred to high rotational speeds of the pinions, he says.
, Associate Professor at KTH, says the flex units are a key feature for the cascade gearbox.
“Besides enabling equal load sharing, these make the transmission compliant, which protects against shock loads,” Björklund says.
Möller says the C3’s performance was proven in grid-connected configuration during a dry testing campaign at KTH last year. The system is now connected to a floating microgrid unit provided by the European Marine Energy Centre (EMEC) in Orkney, Scotland. The microgrid enables the C3 device to behave as if it were grid-connected by providing a stable voltage and frequency reference, simulating the impedance of a typical grid connection, which absorbs power from the device under test and provides power to auxiliary systems.
Once the ocean demonstration in Orkney is completed, the next stage is designing, manufacturing and testing the first full-scale converter in a Stage 4 demonstration project that will run from 2018 to 2020, Möller says.
Source : KTH Royal Institute of Technology