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High Power, high Reliability offshore wind technology

Final Report Summary - HIPRWIND (High Power, high Reliability offshore wind technology)

Executive Summary:
HiPRWind was a project to develop and sea test new structural, component, monitoring and control engineering solutions that would enable very large wind power installations in deeper waters. To gain real sea experience and data, a fully functional floating wind turbine was to be deployed at a European ocean test site.

The first phase of the HiPRwind project involved mostly industrial companies dedicated to designing a floating support structure matching the chosen 1.5 MW wind turbine. This activities covered the detailed design of the floater itself, the mooring system and dynamic cable, the control and operational supervision system. The design process was entirely supported by use of numerical simulation tools.

The results of the design process constituted the working base for fabrication, load out concept development and installation of the whole floating system. In an early phase of the project, the construction of the steel parts of the floater have been started.

However, during the third period of the project, two key partners in the project first announced their suspension of work on HiPRWind and then formally withdrew from the Consortium on 30 June 2013. Therefore, the work plan for the remainder of the project required a complete revision. The focus was now on the replacement of those two key partners (and also of a partner, who left the project within the first year), and the search for new partners who could assume the tasks and contributions (wind turbine hardware, transport services, etc.) of the partners who had left. During the entire third period, even in a suspended period from May 2013 to October 2014, intensive planning and negotiation work has been done by the HiPRwind partners to re-distribute work, budget and tasks.

The project was re-started in October 2014. The amended Work Plan / Consortium included three new Spanish industry partners and collaboration with Norway’s national research infrastructure project on floating wind, FlexWT, with is led by HiPRwind partner NTNU and with which a Letter of Intent had been signed. A new installation site was identified off the coast of Norway, where continued use of the research platform would be possible even after the regular end of the HiPRwind project in 2017, thus guaranteeing continued access to the HiPRWind platform as well as R&D results originating from it.

The circumstances described above required a design review to guarantee safe use of the HiPRwind test floater for an extended test period at the new site in Norway. A detailed analysis of the time constraints and associated risks was performed by both the HiPRwind and FlexWT partners for an extended period until March 2015, including several meetings between the consortia. Unfortunately, in the end, both the FlexWT and the HiPRWind projects identified too high risks for the consortia to continue with the work.

Without having a floating wind turbine for testing purposes, a termination of the HiPRwind project was inevitable. In an extraordinary General Assembly Meeting, the HiPRwind Consortium decided to request the termination of the HiPRwind Project, which has been accepted by the by the Commission taking effect on 30 June 2015

Project Context and Objectives:
The HiPRWind project aimed at advancing the state of the art for multi-MW wind turbines offshore and in particular floating wind turbines. With a consortium of industrial companies, SME’s, R&D organisations and universities, the design, fabrication, installation and operation of a MW-class floating wind turbine for research purposes was to be conducted. The beneficiaries in the HiPRWind consortium are listed below:

- ABB (Switzerland)
- Bureau Veritas (France)
- IDESA (Spain)
- Technip (France)
- Vicinay Cadenas (Spain)
- Ingeteam (Spain)
- ALE-Spain (Spain)

- Micromega (Belgium)
- Dr. techn. Olav Olsen (Norway)
- Wölfel Beratende Ingenieure (Germany)
- 1-Tech (Belgium)
- QiEnergy (Spain)

- NTNU (Norway)
- University Siegen (Germany)

Research Organisations:
- Fraunhofer IWES and IKTS (Germany)
- Narec (now ORE Catapult, UK)
- SINTEF (Norway)
- Tecnalia (Spain)
- TWI (UK)

The first phase of the project was focused on a detailed design for a floating support structure matching a 1.5 MW wind turbine. The results of Work Package (WP) 1 were the base for Work Package 2, where fabrication led by IDESA, load out and installation of the whole floating system should be undertaken. The operation of the floating turbine was the scope of Work Package 3 under Tecnalia’s lead. This was to cover the development, installation and operation of a comprehensive measurement system. Tecnalia would maintain operation of the wind turbine and of the sensor systems for at least one year to the end of the project.
Following commissioning, this unique research tool should be available to researchers also beyond the consortium under a shared access scheme and would provide a huge amount of field test data and valuable experiences for all aspects of floating wind turbines, e. g. the commissioning, the load out / installation, the maritime operation & maintenance. These results would feed into the R&D Work Packages WP4 (Advanced floater and moorings systems), WP5 (Controls, Power and Grid), WP6 (Condition and structural health monitoring) and WP7 (Advanced Rotor Concepts). The developments and theoretical results of these WPs could be evaluated with the field test data. Finally in Work Package WP8 (Turbine concept generation) all findings in the R&D should be summarized as related to 10 MW-class floating platforms.
Along with the scientific and technical work packages WP1 to WP8, the dissemination of the results has been conducted in Work Package 9. This WP9 developed and supported the public web site of the project and bundled all dissemination activities in the project. Work Package 10 conducted all required information management activities (preparation of public scientific reports, support of partners with regard to external information activities, etc.).

Project Results:
1. Floater Design
1.1 Concept selection
From the very beginning of the platform concept development in the HiPRwind project, spreadsheet models have been established to take into account global dimensions, weights and preliminary dynamic behavior of different floating platforms. The main specifications of the designated test wind turbine such as its mass, nacelle and rotor inertia, description of the moment on the structure caused by the electrical torque, forces and moments exerted by the wind under different operating conditions have also been considered.
A parametric model of the concept has been established on a spread sheet. Based on a complete description of the geometry, experience data for steel weights, turbine specifications etc., basic characteristics as static stability and heave period have been calculated. The preliminary design requirements were that the static heel angle under maximum wind trust should be around 5 degrees, and the heave period should be approximately 20 seconds. The static heel angle was calculated based on the stability parameter and the mooring line arrangement and response. There are infinite combinations of main parameters that will satisfy these requirements. However, an additional requirement was to minimize the steel weight. Based on experience and parametric variations a combination of main dimensions was sought to minimize structural weight.
The fundamental requirement, however, was to minimize response with respect to dynamic pitch angles and accelerations on the top of the wind turbine tower. This requirement were relates to dynamic loadings on the turbine and its functionality with respect to power production. Another important issue was fatigue of the tower which is directly related to the top mass acceleration and the dynamic heel angle. For a small turbine this is probably manageable within normal wall thicknesses in the lower part of the tower. For bigger turbines this may become a feasibility issue.
Within HiPRwind, hydro dynamic spread sheet models have been established such that parameter variations can be run very efficiently and quick. This was done by applying a “Python” script. These first spread sheet models have allowed partners to evaluate more than 15 concepts. An evaluation matrix and screening have been proposed defining several evaluation factors like cost (divided into fabrication, material and deployment cost), sea-keeping, size, experience, safety aspect, installation requirements, risks and so on. Finally, a semisubmersible concept was chosen according to this evaluation matrix.

1.2 Dynamic Cable
The aim of the research related to the dynamic cable configuration was to provide a suitable design and configuration to be used, among other things, for power take-off. This was a nontrivial issue as such dynamic cables are prone to fatigue damage, both due to wave action and from induced motions by the floater itself. For an economic and reliable design, the dynamic cable had to be optimized, and among various standard configurations (e.g. lazy wave, lazy S, steep wave, etc.) the most suitable one had to be chosen. Also the connecting point and type of connector had to be designed.
The design of the cable depended on site conditions, on the floater design and on the floater dynamic characteristics. In particular a dynamic analysis of the floater motions was needed, in order to obtain the motions induced in the cable. For the first floater design in project year 1-2 the most important performance requirements for the dynamic cable were fixed. These included constraints on the allowable floater motions in all relevant degrees of freedom, and were to some extent a compromise between reliability considerations and the goal of maximum power production. These requirements were developed by ACCIONA Energia, who also proposed three options of connecting the cable to the floater. At the time of the termination of the HiPRwind project there were still uncertainties regarding the wind turbine to be used finally, its control system, the final floater design and the environmental conditions. Therefore, the final design of the dynamic cable could not be executed.

1.3 Final Design
The Final Design of the HiPRWind floating platform contains several main aspects as the structural design influenced by all relevant aspects from Met-ocean, Geophysical and Geotechnical conditions at the site of employment, to the Mooring, Transport, Sea-keeping and Stability, Load-Out, Marine Operations, Turbine and Control analysis and their respective design implications. The fatigue analysis was done and the required testing of the welds of the structure to ensure the quality of the build was defined. The Design was calculated and the construction drawings were created from the model.
Due to the fact that certain design details needed to be finalized in dependence of the final details of the marine operations and the dynamic cable design that have not been determined before the termination of HiPRwind, there are certain gaps and uncertainties in the proposed design. There was also a second round of turbine loads present that needed to be used to determine the safety concentration factors for the fatigue check in a second iteration to check that the design actually was valid or if minor changes needed to be implemented to enhance the fatigue performance of certain unions.
The following items were covered by the final design when the scientific and technical work of HiPRwind had been suspended:
• Seakeeping calculations (incl. uncoupled modelling and fully coupled modelling)
• Fatigue life assessment
• Load case analysis
• Stress analysis for joints and tower support assembly
• Model description for brace structural calculations (diagonal and lower braces, stress reduction by brackets
• Design check under extreme conditions
• Dampers
• Substructure Brace System and wind turbine tower
• Door opening in tower base
• Hatch opening in bottom plate
• Ballast system
• Access system
• Corrosion protection system
• Mooring System (installation and calculations for the mooring chains)
• Towing
• Dynamic Cable

2. Platform Manufacturing
2.1 Floater
The fabrication of the floating platform (floaters and heave-plates) had started at partner IDESA’s workshop accordingly to a schedule that expected the assembly of the structure at the port of Aviles, Spain, during the summer 2013. The separately manufacturing of each part of the structure (floaters, heave-plates, braces and central tower) continued following this schedule. Just before the suspension of the project in May 2013, the whole manufacturing process was 30% completed.
In October 2014, the construction of the floating platform was restarted and a new planning was developed in order to meet the challenging deadlines included in the amended Document of Work. Due to the huge size of the HiPRWind structure, some parts of the platform had been stored in different places of Idesa´s facilities during the suspension period. So the first tasks after the re-start of the project were an in depth reconsideration of the manufacturing process and a complicated movement of heavy parts across the IDESA’s workshops.
From October 2014 until the end of the period IDESA worked in parallel in the manufacturing of each main part of the structure. This approach complicates the logistic inside the workshop but it was the only way to meet the deadlines. The planning was to manufacture and paint each part of the structure at IDESA’s facilities and then transport all of them to Aviles port (2 Km far from IDESA’s work shop) where the final assembly would be performed next to the harbor bay. The construction could be completed up to approximately 50% till the decision was taken to terminate HiPRWind.
As the main result of the manufacturing process, a complete set of constructional drawings had been produced, covering all main components: the heave plates, the floater columns, the braces and the central tower. In general, the manufacturing process of each of these components consists on the following stages: cutting of the plates, rolling and welding. Additionally some general preparatory works are required before the starting of the manufacturing process regarding, for example, the preparation of the drawings and the definition of the standards and fabrication documents. The manufacturing process was based on the detailed engineering developed in the framework of above described floater design.

2.2 Wind Turbine
During the second period of the HiPRwind project, work to adapt the existing on-shore wind turbine design AW1500/77 to the harsh conditions of off-shore operation had been worked out. This needed to be done by means of modifications to the tower and fitting out with additional components such as sensors, de-humidifier or sealants. During the course of the project, an alternative wind turbine model was planned to be used (General Electric GE 1.5) which implied relevant changes in the control and power electronic cabinets. in the tower base. Thus, Ingeteam, as leader of this task, retrieved and calculated the data required to validate the tower design as a result of the change of the wind turbine model, due to it is a similar power turbine but a significant different technology.
Ingeteam Service joined this project under the Seventh Framework Programme of the European Union on mid-October 2014. For this reason the first actions had to focus on collecting existing information already developed by the consortium partners prior to our entry into the project. Then an action plan was scheduled to achieve the tasks concerning this deliverable on time, and first steps in this direction were on-going, including design minor changes suggestions, in coordination mainly with Olav-Olsen (floater, transition piece and tower designer), IDESA (floater and transition piece manufacturer), Fraunhofer (who were responsible of the acquisition of the turbine to be used), when the project was terminated.
The experienced gained when carrying the above described work were very valuable, especially for Ingeteam Service as, being a very experienced O&M service provider for onshore wind, is nowadays starting to provide services in offshore wind farms and aims to lead O&M activities in floating wind technology. The main results obtained are:
Marinization of an onshore WT: For an offshore use of a standard onshore WT, a “marinization” process was needed, i. e. the control of environmental conditions, improved sensors, pressurization, special coating, sealants and modification of the cooling system with filters and/or de-humidifier.
Components arrangement: The arrangement of all the components had to be well designed to avoid decommissioning problems in case of failure. Built-in tooling had to be foreseen. Design and built-in tooling was found even more important in floating offshore WT compared with onshore WTs and also more critical than in bottom fixed offshore turbines.
Lifting systems: As jack-up vessels are unable to work in such water depths as foreseen for floating wind turbines, more powerful cranes than usual will be needed both at the landing point in the floater and inside the nacelle, for a wider range of parts able to be replaced.
Floater access redundancy: In some weather conditions it may be not possible to access the platform at a unique landing point, but may be possible if there were landing points at the three columns of the floater, or at least at two of them.

2.3 Mooring System
Due to the suspension of the project in May 2014, the hardware production of the mooring system had been stopped. During the suspension period, the planning of the mooring system has been further progressed, aiming at an installation of the floating wind turbine at the EVE field test site (Basque coast). The re-structuring of the project during the suspension period led to the decision to perform the field testing at the Norwegian field test site for Ocean Energy near Trondheim. Therefore, the mooring arrangement would have required a design revision. This design revision had been started right after the lift of the suspension.
The manufacturing time of the mooring lines was expected to be shorter than the finalization of the floating structure itself. For this reason it was decided to prioritize the floating structure manufacturing re-start in the period from the suspension lift to the project termination. Due to the termination of the HiPRwind project with taking effect on the RTD work in late March 2015, the production of the mooring system never has been re-started.
Since the mooring arrangement and anchor design is strongly linked to a specific installation site, the following description of the technical findings with respect to the mooring system represents the status at project termination. This means that all information given are related to the original selected installation site of the HiPRWind floating wind turbine, the bimep test field at the coast of the Spanish Biscay ( ). Nevertheless, the principle approach can be adapted to other sites as well.
Mooring Arrangement: As a basis for the dynamic response simulations performed with the floater model, a three line mooring arrangement has been selected as shown in Figure 4. Seabed conditions have been considered for the selection of the chain parameters as can be summarised as follows:
3 Mixed lines of 84 and 92 mm chain:
• Line A: 175,0m of 84mm + 380m of 92mm
• Line B: 172,5m of 84mm + 230m of 92mm
• Line C: 172,5m of 84mm + 380m of 92mm
Total chain weight: 250 tons
The anchor design with the major parameters can be summarised as follows:
• Type of anchors: Drag embedment anchors
• Potential supplier: Vryhof (The Netherlands)
• Design to be done but based on MK5 Stevpris/Stevshark.
• Lines 1 & 3: 12 - ton anchors (5 m sediment thickness)
• Line 2: 18 - ton anchor (2/3 m sediment thickness)
• Manufacturing time: 8 weeks

3. Platform Operation and Research
3.1 Operation and Maintenance Protocol
A first approach to identify the main issues and requirements to the floater and wind turbine operation and maintenance (O&M) started for the original emplacement and turbine model. The aim of the O&M protocol was to ensure the optimised prototype operation and safety access and maintenance to maximize the working time for research. For this reason, and to ensure that it would be still valid for the revised conditions of the project (i. e. the new test site in Norway), the previous work developed by the original partners has been be reviewed and checked by Ingeteam Service, who had also added some additional comments, suggestions and recommendations, resulting in a reviewed version of the O&M protocol document.
In addition to the O&M activities, a first approach to a market analysis had been included, taking advantage of QI Energy expertise in this field. For this purpose, a top-down approach has been adopted, trying first to benchmark and make use of the discoveries and conclusions of other in-execution projects related to floating offshore technologies. Then, the O&M solutions in such projects where submitted to a SWOT analysis considering economic factors. A tentative Cost analysis was implemented for the best identified solution. The Key blocks of factors affecting the O&M were also announced and a sensibility analysis was planned to be done to determine the impact of those factors in the increase and/or cost reduction. A set of recommendations was compiled and documented.

3.2 Communication and Data Acquisition
The main aim of the work done was to define a common methodology and deployment strategy for the different monitoring structural health monitoring systems to be installed in the HiPRWind floating offshore wind turbine. It was decided to follow V-Model methodology for the instrumentation and control deployment. The initial objective of the work was to summarize the work carried out in Task 3.3: Communication with the test platform, and T3.4: Data collection and assessment of the floating platform. It was expected to deliver D3.3 by the end of the project with the description of the communications system design and the database –sizing, access to the information, description of the information available.
During the second and third periods of the HiPRwind project, the work was focused on the design of the communication system and the database, in close cooperation with WP6 Condition and structural health monitoring. After several discussions to understand the requirements and different communication protocols of all the monitoring systems developed in the framework of WP6, it was decided on the architecture design of the communication system and the database. A report has been produced, which summarized the communication system and database requirements and the consideration that should be taken into account for the practical implementation of both, the SHM systems and the communications system. This was done in order to ensure the proper operation of the wind turbine and guarantee the data collection for the dynamic behavior of the floating prototype. In this sense there was also a close collaboration to WP2, for the installation and commissioning of the sensors and communications devices for each SHM system. The developed communication system has been based and designed around TECNALIA’s DAS system, which is described in a HiPRwind deliverable.

4. Electrical System
4.1 Frequency Converter
The aim of the electrical system tasks of the HiPRwind project was to develop and test new solutions for very large offshore deep water wind turbines at an industrial scale. HiPRwind involved a number of academic and industrial parties working on various aspects of the electrical system. Challenges identified for the electrical system were as follows:
Typically wind turbines are installed on the land or on the coast line, where water is not too deep. Such installations face numerous problems related to environmental protection and approval of the local people. Wind turbine installation in the deep water will allow to reduce the environmental impact and avoid problems related to approval of the local people. Moreover, since further away from the coast winds are more powerful and stable, deep water installations allow for higher energy production. However, going to deep water offshore installation requires new structural concepts of wind turbine construction, where there is no solid structure connected to ground anymore. Deep water offshore installation requires floating wind turbine structures. This could present special requirements to power electronics converter such as: position in the turbine, size/weight, vibration strength, etc.
Deep water offshore installation means significantly longer distances to the power grid. Longer cabling will result in larger energy losses and voltage reflection issues. As a result, longer cabling poses challenges for power electronics converter design and reliable operation. Design aspects affected will be filter design, reactive power compensation capability, etc. This will impact size, weight and cost. Also, to reduce energy losses, alternative distribution architecture based on DC transmission can be considered. This will affect power electronics converter topology selection and design.
Wind turbine’s maximum power rating today is around 7-8 MW. HiPRWind project was to deliver a fully functional floating wind turbine installation at approximately 1:10th scale of future commercial systems, deployed at real sea conditions. HiPRWind will develop and test novel, cost effective approaches to floating offshore wind turbines at a lower 1-MW scale. So, power of future commercial system should be at least 10MW, which significantly exceeds the biggest state-of-the-art systems of today. This fact challenges existing power electronics converter concepts for wind in terms of size, weight, cost and scalability.
Finally, all mentioned above factors will provide large impact the cost of the wind turbine system. Obviously, the cost of power electronics converter is of concern.
In the electrical research part of the HiPRWind project, the emphasis was given to reliability aspects of MW converter for offshore wind turbines. The Modular multilevel converter (MMC) concept was chosen and its reliability aspects were studied. Advantages of MMC were identified with respect to application – scalability, inherent redundancy, competitive efficiency and potential for low cost. Potential for low cost comes from the fact that a MV converter in MMC topology is realized using cells with much lower voltage rating than the input voltage. For example, 6kV input converter can be realized with 1.7kV power semiconductor devices in the cells. MMC topologies could be realized with standard hardware and have different strengths/weaknesses for the application. To provide high reliability for offshore wind application, particular attention has been drawn to the following:
• methodologies to estimate cell reliability and ways to increase individual cell reliability;
• IGBT module (core power processing device in the cell) lifetime in view of application profile;
• cell energy storage reliability verification. Energy storage (DC link capacitor) in MMC cell has considerable current stress. For offshore wind application, film capacitors must be used. It is important to
• verify DC link film capacitor reliability on the component level. This includes comparison of component designs from different suppliers and accelerated lifetime testing.
• operation of MMC under fault. One of the main MMC features is the distributed protection. So, each cell has an element that is activated in case of fault. Reliable and coordinated protection in MMC is the challenge that requires a lot of attention to design of protection concept as well as verification step.

This following results of the research work done in the frame of HiPRWind project on advanced high-power power electronics conversion stage systems for deepwater offshore wind turbine have been achieved:
• reliability methodology analysis and failure rate calculation for MMC cells;
• lifetime estimation for IGBT module in MMC cells for wind application;
• reliability testing consideration for energy storage capacitor in MMC cells;
• evaluation of SiC device application for MMC converter;
• theoretical and experimental results of investigation on MMC converter operation under fault.
• application of ANSI-VITA51.1 quality factors for MMC cell failure rate calaculation allows to focus designer attention on small number of high FIT-rate components (ICs, optocouplers, etc.) and their design rules in relation to reliability;
• based on assumed wind profile, both MMC topologies demonstrate theoretical IGBT module lifetime well above 20 years of operation;
• for reliability testing of energy storage film capacitor, it is important to have tests to check against design flaws as well as accelerated lifetime tests;
• Hybrid solution (SiC active device + Si diode) gives a certain benefit in terms of semiconductor losses for MMC cell at a given specification. However, SiC must really deliver large benefits also on the system level to offset the drastic pricing difference;
• Fault tests demonstrated repetitive 100ms-long operation of the prototype. The results obtained serve as an input for protection design to identify worst-case scenarios and associated margins required.

5.2 Grid Integration
In the frame of the electrical grid research activities, a report has been produced, which provides an overview of grid connection options for large offshore wind farms, and presents detailed investigations of case studies addressing novel solutions for wind turbine converter systems and HVDC transmission systems. Regarding wind turbine and collection grids, Square Wave High Frequency converters have been analysed as a promising alternative to get medium voltage DC power output from wind turbines. The main benefit of such solutions is the potential cost saving promoted by the use of simpler and cheaper DC cables in the collector system, smaller and lighter high frequency transformers and the possibility of removing the offshore substation in those wind farms where this is feasible.
The behaviour of such converters has been analysed. The voltage and current waveforms were described in detail, and the relation between input and output voltage dependency on converter parameters was studied. Four converter prototypes have been implemented and different configurations have been tested in a laboratory setup to validate the concept. The use of the leakage inductance of the transformer as an inherent element of the converter to shape the current waveforms was discussed. The analytical expression of the relation between the converter input voltage and the output current was developed, as a function of the main converter parameters.
The converter has no control parameters and the input converter DC bus voltage varies with the HVDC line voltage and the output current. With conveniently chosen parameters the converter can operate in open loop. The power losses of the proposed Square Wave High Frequency architectures were also analysed, finding reduction in power losses of direct connection of wind turbines to DC transmission lines, or by using an intermediate wind farm DC grid.
Regarding high voltage transmission to shore, HVDC systems have been analysed, in particular a case study of a 1 GW wind farm connected to onshore connection points in two different countries via a multi-terminal HVDC grid. Emphasis was on modelling and analysis of fault detection and fault-ride-through capability for short circuit and ground faults in the wind farm collection grid, in the DC transmission grid and on AC-sides of the two onshore HVDC terminals.
For faults in the HVDC grid, small required clearing times may be a critical issue for fault-ride-through of the healthy part of the system. In order to assure fault ride-through of the un-faulted parts of the system, DC-breakers are required. For faults located on the branch between the wind farm HVDC-terminal and the terminal with constant DC-voltage control, the required disconnection time was found to be very short and critical for DC breaker choice. Another issue is that faults close to the converter stations were seen to cause very large currents in the anti-parallel diodes of the semiconductor switches. To prevent damage, the required disconnection times for phase-to-phase faults were found to be less than 1 ms. for the worst cases, and a few milliseconds for phase-to-ground faults. This appears very difficult to achieve in practice. However, with other topologies, especially the modular multilevel converter, the large current due to discharge of the capacitor in the phase-to-phase fault cases could probably be avoided.
Distance protection appears suited for use in the wind farm collection grid, despite the low short circuit levels of the converter interfaced generators. However, there could potentially be problems with this type of protection in smaller wind farms with converter interfaced turbines. The solution would then be to use differential protection.

5. Structural Health Monitoring
With respect to the structural health monitoring (SHM), a comprehensive concept for the sensor equipment on the platform and on the wind turbine has been worked out. The Sensor networks on test beams, blades, tower and floater was designed to be the backbone for structure-integrated SHM system for rotor blades and critical parts of tower and floater. Starting with base conditions of the blades ensured by NDT-methods, a model-based and integrated SHM system should lead to a condition-dependent and predictive maintenance.
The main aspect of operation a floating wind turbine is the survivability of the entire structure under harsh sea conditions. Due to the movement of the floater under the influence of wind, waves and tidal currents, the wind turbines will be exposed to completely different structural load as when installed on solid ground. Therefore, an extensive SHM system was supposed to be installed on the floating turbine. The dimensions as well as the sea environment were setting advanced requirements to the robustness of the sensors, cable, etc., to the electro-magnetic compatibility (EMC) and the resistance to salty air and humidity, lightning strikes, vibrations, etc.
The SHM system design was composed of a sensor network and different simulation models with the following features:
• A combination of acoustic and vibro-mechanic methods. The sensor system is based on optical (FBG resp. polymer) components, piezo-electric transducers and MEMS-sensors which are integrated into the structure or applied to components during their respective manufacturing.
• Combination of data from SHM system with machine-dynamic load data from gearbox, main bearing and generator coming from CMS to one complex monitoring system.
• Optical based communication and optical energy supply of sensor network (i.e. no copper cabling) to assure lightning protection.
The methods of installation of the sensor systems for surface mounting and embedding have been be refined, resulting in a reproducible controlled process. This included recommendations for adhesives, substrate preparation and fibre protection, ensuring a high quality of strain transfer from the substrate to the fibre. Fibre protection methods have been developed with special consideration given to harsh offshore environmental conditions.
The multi method network sensor system to be implemented in the structural components was based on optical fibres (Fibre Bragg Gratings or polymer), piezo-electric transducers and accelerometers which are integrated in structures or applied to components during their manufacturing. The load monitoring system required a sensor set-up consisting of strain and acceleration sensors. Furthermore, the Operational Modal Analysis (OMA) required distributed sensors along the tower and the blade and knowledge of the environmental and operational conditions.

6. New rotor Concepts
The major focus for the work on new rotor concepts was the investigation of structural design techniques and hardware ‘add-on’ solutions towards tailoring loads on the wind turbine rotor blades but also maintaining the power production. The envisaged load mitigation and therefore material savings on all the turbine structural parts was expected to contribute in the costs reduction of the off-shore wind turbines.
For simulation purposes, a costal high wind speed field was selected in order to comply with the offshore high mean speed values terrenes. These data were one of the few public available wind speed data with a track record for over 20 years. The data were statistically analysed and used as input for the wind turbine blade design evaluation.
Passive bend-twist coupled blades and their implementation was investigated in the literature. An IWES in-house numerical aeroelastic code (Modelica) was extended in order to support the theoretical background for the load calculation on structurally bend-twist coupled blades.
A reference wind turbine was selected i.e. the NREL 5MW and the installed blade design model, based on the WMC-Delft design, was evaluated towards structural integrity according to international standards. In a preliminary analysis the reference design was modified implementing UD off-axis layers in the load carrying girders in order to induce laminate-material driven bend-twist coupling.
Moreover, passive dampers were designed and manufactured in order to be installed in wind turbine rotor blades in order to eliminate the wind induced oscillation amplitudes, contributing in the load mitigation conceptual strategy.
Wind turbine rotor blades are operating under very high fatigue loads. A structurally tailored load mitigation design could conceptually enhance the operational life of the turbine while contributing in the overall mass reduction and thus in the material-installation costs. A passive bend-twist coupling strategy of the rotor blades deflections is investigated including the tools development for the fatigue loads and equivalent damage calculations.
The initial design goal was the generation of load series with a reduced load case set that could be used for fatigue load calculation. The loads analysis for the reference NREL 5-MW turbine is performed with the aero-elastic wind turbine simulation tool FAST (Fatigue, Aerodynamics, Structural & Turbulence) by National Renewable Energy Laboratory. The bend twist coupled structural performance was preliminary simulated with ANSYS FE software and a 3D shell element model analysis. Moreover an advanced beam element was developed based on Timoschenko’s theory in order to be implemented in the IWES aeroelastic code OneWind.

7. Upscaling Boundaries
The high energy demand, requirements for higher power stability and the on shore land ‘saturation’ enhanced offshore wind park projects expecting higher annual energy harvest due to the increased mean wind speeds. The perspective for the annual installed power in 2050 is 50% onshore - 50% offshore. However, at the same time the ‘wind’ project has to be developed in a reliable, cost effective and environmentally friendly, accounting for the technological barriers that have to be overcome. This means that the wind turbine should be optimized in terms of material usage, survive under the applied loads, harvest the most out of the wind power and perform reliable for at least 20 years.
Despite the limited offshore experience, the wind turbines have been developed since 90’s accumulating a great amount of know-how in design, manufacturing, installation and commissioning. Although it is not always possible to project the past into the future, the restrictive factors underlying the development up to know can enhance our understanding and help in answering questions like:
• ‘What are the driving forces?’
• ‘Should we go for larger turbines?’
• ‘Can we upscale?’
• ‘Which are the technical barriers and bottlenecks?’
• ‘Which parameters have to be optimized?’
A basic financial approach was performed, focusing on the effect of the major structural parts on an offshore farm costs along with the operational and maintenance expenses. Technical barriers were discussed in terms of manufacturing, installation, design tools, available manpower, addressing for the future development challenges with respect to:
• Cost of Energy-Upscaling
• Wind turbine blades
• Logistics/Installation
• Pitch system
• Hub
• Drive train: Gearbox – Direct Drive, Generator
• Yaw system
• Tower - Substructures
• Electrical infrastructure
• Operation& Maintenance

Potential Impact:
HiPRWind has made significant achievements despite being unable to complete its platform and the research program it was designed for. Technical areas where exploitable project results have been achieved are:
• The platform design & engineering, which contains a number of technical innovations relative to the state-of-the-art in semi-submersible wind floaters. It allows reducing the amount of steel used by 40% compared to the original estimations. The design can be scaled to 5 and 10 MW and was fully engineered for the Bimep site. The platform was found to be transferable to the new intended site off the coast of Trøndelag (Norway).
• The operational planning, including platform load-out, towing to the installation site, installation of mooring system, anchors and dynamic cable. The planning was almost fully completed for the original site (Bimep, off the Basque Country. Spain) and partly done for the Trøndelag site.
• The multi-MW power converter. This has been fully developed in HiPRWind and is the basis for a next generation of products for large offshore turbines, being commercialised by ABB.
• The floating turbine controller software, which has been defined, presented at a major industry conference and later published as a peer-reviewed article all within HiPRWind.
• The study of grid stability of large VSC-HVDC connected GW-size offshore wind farms, which was fully developed and in a manner similar to item (4.) has been presented and subsequently published as a peer-reviewed paper.
• The condition monitoring system, an SME-developed and IP-protected technology fully designed for the HiPRWind platform, featuring an unprecedented level of integration in the collection, analysis and interpretation of structural health data.
• The Shared Data Access, a set of guidelines outlined in HiPRWind for offering access to field data without risking to compromise EU competitiveness, as might result from full public access that is open also to the competitors of European industry and R&D.

1. Heritage of the HiPRWind platform design & engineering
Positive impacts of HiPRWInd are already affecting other activities in European offshore wind R&D. HiPRWind partners are continuing to innovate and capitalising on the achievements of the project. Here we describe two examples of this “heritage”, namely INFLOW and Nautilus.
The FP7 demonstration project INFLOW, focused on vertical axis floating turbines, started in June 2012. This €21.5m project was led by Technip, a HiPRWind consortium member. The design influence from the HiPRWind floater on the triangular semi-submersible carrying the INFLOW VAWT, is quite direct. Locating the powertrain and other heavy components at the tower base gives a favourable center of gravity compared to a conventional HAWT, resulting in numerous technical advantages for semi-submersible floaters in carrying a vertical axis turbine, if these would one day hit the market.
Tecnalia, also a HiPRWind consortium member, applies experience from HiPRWind in development of its floating platform NAUTILUS. A spin-off company, NAUTILUS Floating Solutions, is dedicated to the development of a floating platform for a 5MW wind turbine. This regional industrial venture is thereby benefiting from lessons learned and experience gained in HiPRWind. In particular, the experience has led to an optimized design of the NAUTILUS floater which has passed through several tank testing campaigns and verifications, and it has also been beneficial in clarifying the permission process for the demonstration at sea.
Outside of Europe, HiPRwind has had extensive interactions with Japanese floating wind developers in the Fukushima Forward consortium, including several bilateral and one EU meeting. Participants from Germany, Norway and Spain are focusing on Japan as a presumed early market for deep water wind solutions. While operational solutions for the Japanese projects are different, it is believed that the input from HiPRWind has been significant and will grow further, with expected substantial export opportunities in the years and decades to come.

2. Further steps to exploitation
The above two examples start from the design and engineering results in the HiPRWind Deliverables 1.1. and 1.3. Two further examples are in component-level innovations, in which power controllers for the offshore wind power sector is a fast growing market segment already worth billions of Euro per year whereas Structural Health Monitoring is a relatively newer market segment but also set to grow very large considering the potential cost savings in O&M.
To continue promoting exploitation of HiPRWind results, members of the HiPRWind consortium will continue to present information about HiPRWind and their role in it to industry and authorities, and to business partners with whom they are discussing new developments to establish new business in the emerging deepwater wind industry. As joint owners of the Foreground, HiPRWind partners enjoy full rights to use it. This is becoming more important as the interest in floating wind is rebounding.
Exploitation of the project results requires addressing the following five basic questions that each joint owner must consider based on their business model and priorities:
• What are the project results that can be exploited?
• Why? What is the aim of each partner’s individual exploitation effort?
• To whom? Which of our business partners are ideal partners? Together with these, we can identify target market(s), target groups and end users suitable for the exploitation.
• By whom? Are there project outcomes can be exploited by the Consortium as a whole, or by a smaller number of former HiPRWind participants working together?
• How? Which exploitation mechanisms are to be used for each type of exploitable result?

The ways and means of IP exploitation will necessarily have to be decided ad hoc in this situation. The HiPRWind participants have remained in collaboration until termination, are active in the same industry, and collaborating in many other funded projects, all of which bodes well for the future.
Consortium members will also integrate HiPRWind developments into their ongoing research, educational and commercial activities. The most important general considerations are:
• Economic impact resulting from industrial activity and commercialisation of products developed based on project results, future sales of derived products and/or services.
• Increase in development/operational efficiency for consortium members with regards to projects/operations deriving from HiPRWind to be developed in the future.
• Business allies/partners who can be helpful in exploitation: The Consortium Agreement allows full commercial use by HiPRWind participants of their jointly owned foreground.
• Use of new findings/technologies/innovations for further R&D and innovation.

3. Contribution to Certification and Standards
Whilst the platform was a one off R&D tool and not intended to be certified as such, the engineering was monitored by the certification company Bureau Veritas as a HiPRWind consortium partner. The HiPRWind work has informed a BV ”Guidance note on floating offshore wind turbines”, no. NI 572, published in 2011.

4. Dissemination of Results
The public web site has been kept updated throughout the duration of the project, including updates to the timeline, work scope and partner descriptions. Stories selected or written to give factual, constructive views of the HiPRWind progress towards achieving the goals were released. All public deliverables can be found under The current planning is to keep the public web site alive for as long as possible after HiPRwind.
In addition to general information broadcast via the web site, the following dedicated dissemination materials have been published (these can also all be downloaded from
• 8 conference presentations
• 2conference posters
• 4 scientific Journal Articles with review
• 7 presentations at meetings or events
(including invited presentations and invitation only events)
• 5 industry or technical (but non specialist) magazine articles
• 3 general interest and mainstream press articles or similar coverage
• 3 other dissemination actions (brochures, flyers etc.)

List of Websites:
Public Project Web Site:
Public HiPRwind deliverables:

Contact information (Coordinator):
Fraunhofer IWES, Germany
Tel: +49 561 7294 0
Fax: : +49 561 7294 100