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Advanced Braking Module with Cyclic Energy Recovery System (CERS) for enhanced reliability and performance of Wave Energy Converters

Periodic Reporting for period 2 - WaveBoost (Advanced Braking Module with Cyclic Energy Recovery System (CERS) for enhanced reliability and performance of Wave Energy Converters)

Reporting period: 2018-05-01 to 2019-10-31

WaveBoost aims at providing a step-change improvement to the reliability and performance of PTOs (Power-TakeOffs), by developing and validating an innovative braking module as part of the advanced waveboost PTO system. While built and tested on the platform of the existing CorPower technology, the advanced waveboost PTO system can be integrated in many types of Wave Energy Converters (WECs). Especially for point absorbers - undisputedly the WEC type with best prospects for large-scale development - WaveBoost will solve a central reliability challenge, the so called 'end-stop' problem (excessive, uncontrolled forces when linear movement reaches end of stroke). Further, dedicated reliability assessment methods will be developed and applied. The advanced waveboost PTO system will allow WECs to absorb more energy from a large bandwidth of wave heights and lengths. Similar systems are being used in other sectors (e.g. automotive) but have not been applied to ocean energy. The additional damping force required to safely stop the motion of WECs in storm waves may be several times larger than the PTO force used to convert wave motion into electricity. By providing the extra damping provided by the advanced waveboost PTO system, system survivability and reliability of critical components are significantly improved. Another consequence is a size reduction of the PTO for the same power rating, and an increase of the Annual Electricity Production (AEP). The technology allows WECS to operate at higher average loading, increasing average conversion efficiency. Further, the grid compliance of electricity produced is significantly improved through enhanced power production control via directly coupled gearbox and generator arrangement allowing greater torque control, reduced complexity and higher reliability. The improvements described above are expected to significantly reduce shock loads on WECs, increase in AEP of 25% and reduce LCOE more than 30% compared to the state of art.
The advanced waveboost PTO system has been evaluated through an initial risk and failure modes analysis, where critical components and functions were identified. These critical components have been further analyzed and evaluated for reliability and robustness, as input to the continued design, prototyping and test program. The system reliability is critical to get to a point where a third party can issue a statement of feasibility, and the test program is designed to secure robustness as well as functionality and efficiency. The time domain model has been developed an iterated through several design proposals to give correct design input in terms of design load cases, component dimensioning and selection and system architecture. The numerical design and parameter tuning is an ongoing activity that will ensure LCOE optimization of the system.

The WaveBoost project has brought together a consortium of sector leaders from Sweden, Portugal and the UK. This deliverable has summarised the key outputs of the WaveBoost project, including key lessons learned and scope for future work. These key project outputs can be summarised as:
• Design of the advanced PTO, including an advanced braking system for greater control of movement and a 98% reduction on overall flow losses.
• Development of HIL-rig and test plans for the advanced PTO.
• FMECA and VMEA analysis of advanced PTO informing design and testing processes.
• Detailed modelling of advanced PTO within multiple wave energy applications.
• Accelerated testing of seals within a bespoke, state-of-the art Seal Test Rig, resulting in a 70% improvement on seal friction.
• Biofouling and corrosion testing in a real sea environment.
• Estimated 21.3% to 26.9% improvement in AEP, based on a target power matrix still undergoing validation.
• LCOE analysis undertaken of three array sizes; 50MW, 300MW and 1GW. Estimated 18.0% to 29.3% reduction in LCOE.
• Lifecycle analysis undertaken of a 50MW array deployed in Scotland, resulting in a carbon intensity of 31.4gCO2e/kWh comparable with other renewable technologies and over 10 times less than conventional gas turbines.
• Socioeconomic analysis undertaken of a 50MW array deployed in Scotland, resulting in €166M GVA and 2088 job years supported.
A) The Advanced Waveboost PTO system for Wave Energy Converters
In response to the R&D needs identified, the WaveBoost project will focus on developing a new subsystem to deliver significant and measurable improvements in reliability and survivability, performance and cost. As an additional benefit, and further contributing to improvements in cost and availability, significant improvements in grid integration will be delivered. The advanced waveboost PTO system consists of building blocks that are well understood in other sectors including automotive, air-planes and rail road infrastructure but has, to date, not been applied to WECs. This provides the opportunity for a new generation of end-of-stroke braking system, delivering improvements of the current state-of-the-art. In many cases, it can be argued that for the wave energy sector no performance benchmarks are yet established. It is the ambition of WaveBoost to fill this gap in key areas for credible future predictions, as well as set higher limits of performance indicators already existing.

B) A new business model
During the development of CorPower Ocean’s WEC technology, the interest from other developers as well as other industries have led to the consideration of a new business model for CorPower Ocean: that the technology development may be better valorized by being a supplier of PTOs or subsystems instead of being a full WEC system supplier. Such shift could allow for better focus and optimization of resources and skills, while reducing the high uncertainty both upstream (technical risks and funding) and downstream (market risks). In the short term however, due to the lack of commercial wave energy systems where the advanced waveboost PTO system could be integrated and due to the lack of verification in full scale, CorPower Ocean is continuing with the development of the entire WEC system. Once proven in first arrays, the opportunity to narrow the focus to the PTO or subsystems may be attractive.

C) An advanced hardware-in-the-loop (HIL) test rig for WECs
Further advance to the sector will be providing new methods and testing infrastructure. By enhancing the HIL test rig with a wet chamber, the project will enable EMEC to provide valuable new services to the industry, providing a new infrastructure to accelerate technology development at a lower cost and risk.

D) New and improved methods for the sector
Also, the application of reliability assessment and improvement methods from other sectors including automotive by RISE (VMEA, see WP 6) and offshore wind by EDP will be established for wave energy converters and first benchmarks provided to the sector, advancing the sector's credibility. Methods and tools on performance assessment (WP5) and LCOE modelling (WP6) will also be enhanced and validated, allowing WAVEC and the University of Edinburgh (UEDIN) improve their services.
WB flyer
WEC deployment
WEC deployment