Introduction to InfinityWEC

InfinityWEC is the first “smart” wave energy converter to use flywheel energy storage to provide power take-off force control in combination with a constant / time shifted output power. The technology comes from the automotive industry where it is referred to as a Regenerative Braking System (RBS), or Kinetic Energy Recovery System (KERS).

KERS applied in wave energy enables the power take-off (PTO) force to be optimized in every individual wave. Advanced control strategies based on wave prediction (LIDAR), model prediction, AI and machine learning is used to provide the following advantages:

  • Increased power output: By providing advanced phase control capabilities (using energy storage to manage power flowing back and forth through the PTO in every wave).
  • Improved reliability and survivability: By controlling the buoy motion to avoid hard end stops and snap loads in large waves.
  • Reduced cost: By limiting the maximum force, velocity, power and stroke-length in the PTO system.
  • Increased revenues: The inherent energy storage in the system adds the capability to provide flexible / time-shifted output power. This enables the output power to be controlled to assist frequency regulation and other gird stability services, increasing the revenues from produced electricity.

Compared to offshore wind power, InfinityWEC is highly cost competitive, offers >10 times higher capacity per used area, has virtually no visual impact and provides a more stable energy supply with less intermittency.

The challenge for wave power

The general challenges for wave power are similar to those of off-shore wind: cost competitiveness with existing generation forms, grid connection, engagement of a dedicated supply chain and new challenges of working and operating in hostile marine environments.

The fundamental technical challenge with wave power is the slow oscillating motion and random variations in wave size and energy content, making it difficult for WECs to recover wave energy efficiently.

It is also a challenge to design robust and reliable systems for the harsh marine environment. A wave energy converter must be able to perform in a wide range of conditions, survive in storms, and operate unattended.

InfinityWEC solution

InfinityWEC is a point absorbing wave energy converter using six ball screws to convert linear motion into rotary motion. Rotating ball nuts with direct drive motors are located on a platform inside the buoy.

The PTO is held in a fixed vertical position by the mooring system while non-rotating ball screws (fixed to the buoy hull) are pushed up and down through the PTO platform when the buoy is set in motion by the waves.  A lead screw connects the PTO platform to the mooring system and is used to adjust the height of the PTO, to adjust the ball screw system for tidal variation and to submerge the WEC to secure survival in storm conditions.

A riser pipe from the oil & gas sector is used as a mooring system, an arrangement which provides a protected route for the power and communication cables inside the mooring pipe and minimizes the bending of these cables which is an issue with suspending dynamic cables from the hull used by other WECs.

Main sub-systems

  • Kinetic Energy Recovery System (KERS): With direct drive ball nut motors connected electrically to a Teraloop flywheel energy storage
  • PTO platform: Vertically fixed on top of the mooring cylinder with a lead screw
  • Heave actuation system: Non-rotating ball screws moving up and down with the buoy hull
  • Level actuation system: The lead screw is used for adjusting the height of the PTO platform above the mooring cylinder, to: 1) align the PTO when tidal level changes, 2) submerge the WEC to survive in extreme wave conditions
  • The riser pipe mooring system: seals the hull from sea water and provides a protected route for the power cable and minimized bending fatigue

Teraloop flywheel energy storage

The novel Teraloop flywheel is based on an outer-rotor design integrated with a permanent magnet motor / generator. The rotor is supported by a magnetic levitation system and electromagnetically stabilized to handle movements, in a similar way as magnetic high-speed trains.

The Teraloop flywheel energy storage design offers a unique combination of high power, high energy and sufficient charge/discharge cycles to last for the 20-year design life of a wave energy converter.

The outer-rotor design improves the energy-per-unit-mass beyond the capability of existing flywheel designs. This makes more effective use of materials and allows a more compact design.

Specification

  • 500 kW maximum continuous power output
  • 10 kWh useful energy storage
  • 5 meter stroke-length in heave system
  • 8 meter stroke-length in level system
  • 3 MN maximum dynamic PTO force
  • 450 m3 buoy volume
  • 120 ton total weight excluding foundation

Patents

OHT´s patent portfolio comprises 8 patent families and is protected world wide. The patents covers all aspects of the InfinityWEC system in different variations. A special focus is how energy storage technologies can be integrated in the power take-off to provide force control features and power smoothing.

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