Work Package 3

Power take-off  reliability and performance, validation of new turbine


Initial turbine operation tests, Kymaner

Objective: Increase OWC turbine annual mean efficiency 50% and improve reliability of PTO.

In offshore wind, operation and maintenance is about a third of the cost of electricity. Electrical components are those that fail most often and increasing their reliability is vital to reduce cost. For wave energy this will only happen when these components’ real operating conditions are known.

Another challenge for OWCs is the low efficiency of the air turbine, below 50% for current OWCs operating in rapidly reversing flow. Lab results indicate that the novel bi-radial turbine could improve conversion by 50% and the successful validation in open-sea will enable the demonstration of reducing cost of energy by 30%.

For these purposes, this Work Package will:

  • improve reliability of the power take-off: collect and share electrical component operating data, identify failure modes, their root causes and test solutions
  • increase annual mean efficiency 50% by advancing the novel bi-radial turbine to TRL5
  • be developed taking into account the expected working conditions and loads in a real ocean environment
  • include a cylindrical axially-sliding stop valve in series with the turbine, acting as an emergency device in order to improve the protection of the Power Take-off Unit in case of severe storms

Task to be performed

Aerodynamic design of turbine, design and specifications of electrical equipment

Computation fluid dynamics (CFD) software will be used to design the turbine and determine main dimensions and detailed geometry of stator and rotor blades. Design requirements include wave energy absorption hydrodynamics, control strategies and mechanical constraints.  The optimal trade-off between generator cost and lifetime will be determined. Indeed, in wave energy application a smaller generator that may run over rated capacity during short peaks but will function closer to its optimal range most of the time may result in lower cost of energy and the project offers an opportunity to validate this approach in open-sea operation. Options for energy storage (turbine flywheel or supercapacitors) will be assessed in order to reduce components operating requirements and lower costs.

Mechanical design, manufacture and laboratory testing of bi-radial turbine

Applicable rules and standards will be used to ensure appropriate turbine design and manufacture for open-ocean operating conditions. Built-in sensors will measure rpm, pressure differential across rotor, vibration and generator temperature, voltage and current. The bi-radial turbine will be tested in a Turbomachinery Laboratory in varying unidirectional flow. Measurements including pressure differential, flow rate, power output will validate and/or refine CFD simulations results and turbine and generator performance will be assessed.

Testing at-sea operation at the Mutriku shoreline wave power plant

The turbine-generator set, the frequency-converter, an air pressure sensor and an ultrasonic free-surface level sensor will be installed on one of the OWC chambers of the Mutriku shoreline wave power plant. Winter waves at Mutriku will be a stringent test for the turbine and electric components reliability, uncovering inevitable first-off design weaknesses and correcting them at a small fraction of the cost of an offshore maintenance operation. Turbine performance will be assessed. Also, there will be collected extensive data on drivers of components fatigue such as high rpm and accelerations; electrical, temperature and pressure load cycles; humidity in the cabinet (which exacerbates electrical stress damages); rate of salt accumulation and corrosion; and these will be fed to preventive and conditions-based maintenance models. There will be investigated the root cause of fatigue drivers, counter-measures will be proposed, tested and assessed at a fraction of the cost and time of open-sea testing.

Open-sea testing of turbine and power conversion chain on a floating WEC

The bi-radial turbine will retro-fitted to the WEC for open-sea deployment at bimep and equiped with the sensors used at Mutriku to measure rotation speed and torque to assess turbine efficiency. Low-frequency accelerometers will be mounted to assess loads due to gyroscopic effects on the turbine-generator rotor and bearings. As in the previous task, there will analysed data on fatigue drivers of electrical components, implemented control algorithms in the PLC and assessed electrical components performance.

Involved Partners

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 654.444