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PowerKite - Power Take-Off System for a Subsea Tidal Kite

Periodic Reporting for period 2 - PowerKite (PowerKite - Power Take-Off System for a Subsea Tidal Kite)

Période du rapport: 2017-04-01 au 2018-12-31

Tidal streams and ocean currents offer safe, reliable and locally produced renewable energy. They are predictable, global and energy-rich.
The Powerkite project designed, built and deployed a power take-off system (PTO) for a novel tidal energy conversion concept, the Deep Green subsea tidal kite. Deep Green produces electricity from slow tidal and ocean currents by a unique principle. By sweeping a turbine across a large area, at a speed several times the speed of the water current, Deep Green adds a step of energy conversion compared to other tidal energy technologies.
The overall objective of the PowerKite project was to gather experience in open sea conditions to enhance the structural and power performance of the power take-off (PTO) for Deep Green to ensure high survivability, reliability and performance, low environmental impact and competitive cost of energy in the (future) commercial phases.
The Powerkite project was run in parallel with the DG500 project, in which Minesto developed and deployed the first commercial scale prototype of the Deep Green technology.
The Powerkite project
• successfully developed and verified technology in commercial scale kite in Holyhead Deep and in reduced scale in Portaferry
• increased knowledge in many areas crucial for future development of Deep Green technology, notably the design of the tether, which connects the kite to the seabed , and involved the full multi-disciplinary project team
• performed innovative environmental impact studies that can be applied widely in the ocean energy industry
At the time of this report, the PowerKite project had resulted in 17 scientific publications and conference presentations and two new Ph.D. students.
The Powerkite project was portrayed in a video produced and broadcasted by the Euronews´ research, science & technology program Futuris. The Project was also selected to be showcased at the technical exhibition of the Clean Energy Ministerial 8 (CEM8), 6–8 June 2017, Beijing, China.
The core of the Powerkite project were the electro-mechanical design of the PTO, including a concept design for the complete array layout and grid connection. The project built scale models of selected components for the PTO system and integrated them in a test platform for open sea testing in Strangford Lough, Northern Ireland. Component development was guided by modelling using component and system simulation models developed within the project. Open sea trials played a crucial role in the project with extensive testing in ¼ scale and in the case of fairing profiles included into the actual DG500 tether installed in May 2018, a tether which has been used by the DG500 project since then.
PowerKite has focused on key components of the PTO namely turbine, generator, converter, top joint, tether and bottom joint. Other Deep Green sub systems such as wing, struts, rudders, control system and foundation were omitted from the development scope of work, but they are included as input values/constants in all applicable analyses and reports, such as Life Cycle Assessment (LCA) and Annual Energy Yield (AEY) calculations.
To study the complex interactions on the system level, an overall PTO system optimisation model was developed. Including models for turbine, power conversion and tether and linking them to kite dynamics and tidal flows. The model enables the performance of the kite to be studied and the AEY to be predicted.
In addition to hardware development and refinement, PowerKite has addressed important aspects of ocean energy such as interaction with the environment, levelized cost of energy (LCOE), maintenance/serviceability and array configurations.
• In tests the new three-bladed and seven-bladed turbine designs showed an increase mechanical power output of 31% to 35% compared to the baseline turbine.
• A medium voltage converter for the actual tidal kite application was designed, built and tested. The electrical conversion efficiency of a medium-voltage system will be a few percent better than the low-voltage baseline system and facilitate the integration in an array of generators.
• The tether was redesigned using swiveling segments which was critical for the improvement in power quality and predictability of the flight trajectory control.
• The overall improvement of powerplant energy output from the baseline due to the PowerKite project is calculated to between 15% to 21%, representing the combined effect of the improved turbine, the improvement of the low-voltage system and the increased drag of the improved tether.
• A life cycle assessment was performed on Deep Green. For the base case (based on the DG500 prototype) the global warming potential (GWP) per kWhe produced was 26.2 g CO2 eq, comparable to other marine renewable energy technologies
• Noise measurements and acoustics modelling have improved the understanding of the technology in the marine environment. While the largest variation in noise is from the turbine revolution, overall the ¼ scale kite has limited interference with marine fauna. Essentially, seals would have to be within the kite flying volume (within 62 m of the turbine) where their listening space reduction (LSR) would exceed 90%
• The (LSR) method provides a significant advance to the marine renewable energy (MRE) community as not only can the cumulative noise field from an array of turbine devices be modelled using this approach, the LSR method can be applied to any MRE device.
• No impact on benthic communities were detected owing to the operation and deployment of the infrastructure with the kite at the Minesto site.
• To date no collisions of mammals with the ¼ scale or full scale devices have occurred. While the sonar system is not fully operational, significant advancement has been made to develop an autonomous and user-friendly observation system. It is anticipated that re-deployment of the sonar system in 2019 will be able to detect, track, and differentiate marine megafauna.
• The development of the collision risk model (CRM) will be ongoing beyond the end of the project. A fully three-dimensional, transient model of the kite and animal shape has been developed and published. Work on the CRM will remain ongoing via an Interreg funded Bryden Centre PhD that involves academia, industrial and Governmental partners.
• Components have been simplified to reduce complexity and the associated operation and maintenance costs (O&M) as well as capex costs. The bottom joint development is an excellent example where the design was simplified reducing capex costs whilst retaining the required performance and simplifying the O&M procedures when the joint is connected and disconnected.
• The Powerkite project has guided the decision to shift the focus away from surface structures in the array more towards a subsea infrastructure.
• The Powerkite project deepened the understanding of costs associated with different array configurations and the associated kite design requirements
• The Deep Green technology is suitable for installation sites with low velocity currents, where no other technologies are known to be efficient. Improving the technology (turbine, converter, tether, etc…) will not only lead to an improved performance and lower LCOE, but it will also allow the power plants to operate in even lower flow conditions, expanding the potential even more.
Minesto DG500 commissioning, kite lifted from cradle.
Minesto Deep Green quarter-scale testing in Strangford Lough, Northern Ireland
Euronews Futuris TV featuring PowerKite open sea testing on 22 May 2017.