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Energy from Ocean Waves: Full Scale Experimental Verification of a Wave Energy Converter
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A wave energy converter has been constructed and its function and operational characteristics have been thoroughly investigated and published. The wave energy converter was installed in March of 2006 approximately two kilometers off the Swedish west coast in the proximity of the town Lysekil. Since then the converter has been submerged at the research site for over two and a half years and in operation during three time periods for a total of 12 months, the latest being during five months of 2008. Throughout this time the generated electricity has been transmitted to shore and operational data has been recorded. The wave energy converter and its connected electrical system has been continually upgraded and each of the three operational periods have investigated more advanced stages in the progression toward grid connection. The wave energy system has faced the challenges of the ocean and initial results and insights have been reached, most important being that the overall wave energy concept has been verified. Experiments have shown that slowly varying power generation from ocean waves is possible.

Apart from the wave energy converter, three shorter studies have been performed. A sensor was designed for measuring the air gap width of the linear generator used in the wave energy converter. The sensor consists of an etched coil, a search coil, that functions passively through induction. Theory and experiment showed good agreement.

The Swedish west coast wave climate has been studied in detail. The study used eight years of wave data from 13 sites in the Skagerrak and Kattegatt, and data from a wave measurement buoy located at the wave energy research site. The study resulted in scatter diagrams, hundred year extreme wave estimations, and a mapping of the energy flux in the area. The average energy flux was found to be approximately 5.2 kW/m in the offshore Skagerrak, 2.8 kW/m in the near shore Skagerrak, and 2.4 kW/m in the Kattegat.

A method for evaluating renewable energy technologies in terms of economy and engineering solutions has been investigated. The match between the technologies and the fundamental physics of renewable energy sources can be given in terms of the technology’s utilization. It is argued that engineers should strive for a high utilization if competitive technologies are to be developed.

Place, publisher, year, edition, pages
Uppsala: Universitetsbiblioteket , 2008. , p. 130
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 580
Keywords [en]
wave power, wave energy converter, sea trials, ocean energy, linear generator, point absorber, search coil, wave climate, utilization
National Category
Other Engineering and Technologies
Identifiers
URN: urn:nbn:se:uu:diva-9404ISBN: 978-91-554-7354-9 (print)OAI: oai:DiVA.org:uu-9404DiVA, id: diva2:172943
Public defence
2008-12-12, Polacksbackens aula, Lägerhyddsv. 2, Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2008-11-21 Created: 2008-11-21 Last updated: 2012-11-09Bibliographically approved
List of papers
1. Full-Scale Testing of PM Linear Generator for Point Absorber WEC
Open this publication in new window or tab >>Full-Scale Testing of PM Linear Generator for Point Absorber WEC
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2005 (English)In: Proceedings of the 6th European Wave and Tidal Energy Conference, 2005Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-97841 (URN)
Conference
6th EWTEC conference, Glasgow, August 28-September 3
Available from: 2008-11-21 Created: 2008-11-21 Last updated: 2013-07-31Bibliographically approved
2. Experimental results from sea trials of an offshore wave energy system
Open this publication in new window or tab >>Experimental results from sea trials of an offshore wave energy system
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2007 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 90, no 3, p. 034105-Article in journal (Refereed) Published
Abstract [en]

A full-scale prototype of a wave power plant has been installed off the Swedish west coast and the overall wave energy converter concept has been verified. Initial results have been collected and significant insights discovered. Energy absorption dependency on load as well as output voltage and power is demonstrated. It is shown that great overload capability of the directly driven linear generator is critical, and indicated that, for resistive loads, optimal load does not vary with wave climate. Future grid supplying energy production would necessitate parks of wave power plants in order to reduce power fluctuations.

Keywords
High-current and high-voltage technology: power systems; power transmission lines and cables, Electric motors
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-95683 (URN)10.1063/1.2432168 (DOI)000243582400105 ()
Available from: 2007-03-23 Created: 2007-03-23 Last updated: 2017-12-14Bibliographically approved
3. Wave Energy from the North Sea: Experiences from the Lysekil Research Site
Open this publication in new window or tab >>Wave Energy from the North Sea: Experiences from the Lysekil Research Site
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2008 (English)In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 29, no 3, p. 221-240Article, review/survey (Refereed) Published
Abstract [en]

This paper provides a status update on the development of the Swedish wave energy research area located close to Lysekil on the Swedish West coast. The Lysekil project is run by the Centre for Renewable Electric Energy Conversion at Uppsala University. The project was started in 2004 and currently has permission to run until the end of 2013. During this time period 10 grid-connected wave energy converters, 30 buoys for studies on environmental impact, and a surveillance tower for monitoring the interaction between waves and converters will be installed and studied. To date the research area holds one complete wave energy converter connected to a measuring station on shore via a sea cable, a Wave Rider™ buoy for wave measurements, 25 buoys for studies on environmental impact, and a surveillance tower. The wave energy converter is based on a linear synchronous generator which is placed on the sea bed and driven by a heaving point absorber at the ocean surface. The converter is directly driven, i.e. it has no gearbox or other mechanical or hydraulic conversion system. This results in a simple and robust mechanical system, but also in a somewhat more complicated electrical system.

Keywords
Wave power, Renewable energy, Sea trial, Linear generator, Point absorber, Environmental impact
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-107215 (URN)10.1007/s10712-008-9047-x (DOI)000260967900002 ()
Available from: 2009-07-29 Created: 2009-07-29 Last updated: 2017-12-13Bibliographically approved
4. Catch the wave to electricity: The Conversion of Wave Motions to Electricity Using a Grid-Oriented Approach
Open this publication in new window or tab >>Catch the wave to electricity: The Conversion of Wave Motions to Electricity Using a Grid-Oriented Approach
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2009 (English)In: IEEE Power and Energy Magazine, ISSN 1540-7977, Vol. 7, no 1, p. 50-54Article in journal (Refereed) Published
Abstract [en]

The ocean are largely an untapped source of energy. However, compared to other energies, power fluctuations for ocean waves are small over longer periods of time. This paper present a grid-oriented approach to electricity production from ocean waves, utilizing a minimal amount of mechanical components.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-112949 (URN)10.1109/MPE.2008.930658 (DOI)000262015100004 ()
Available from: 2010-01-22 Created: 2010-01-22 Last updated: 2017-01-25Bibliographically approved
5. Experimental results from an offshore wave energy converter
Open this publication in new window or tab >>Experimental results from an offshore wave energy converter
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2008 (English)In: Volume 6: Nick Newman Symposium on Marine Hydrodynamics; Yoshida and Maeda Special Symposium on Ocean Space Utilization; Special Symposium on Offshore Renewable Energy, 2008, p. 653-657Conference paper, Published paper (Refereed)
Abstract [en]

Anoffshore wave energy converter (WEC) was successfully launched at theSwedish west coast in the middle of March 2006. TheWEC is based on a permanent magnet linear generator locatedon the ocean floor driven by a point absorber. Ameasuring station has been installed on a nearby island whereall measurements and experiments on the WEC have been carriedout. The output voltage from the generator fluctuates both inamplitude and frequency and must therefore be converted to enablegrid connection. In order to study the voltage conversion, themeasure station was fitted with a six pulse diode rectifierand a capacitive filter during the autumn of 2006. Theobject of this paper is to present a detailed descriptionof the existing wave energy system of the Islandsberg project.Special attention will be given to the power absorption bythe generator when it is connected to a non linearload

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-97845 (URN)10.1115/OMAE2008-57415 (DOI)
Conference
ASME 2008 27th International Conference on Offshore Mechanics and Arctic Engineering (OMAE2008) June 15–20, 2008 , Estoril, Portugal
Available from: 2008-11-21 Created: 2008-11-21 Last updated: 2016-04-12Bibliographically approved
6. The Lysekil Wave Power Project: Status Update
Open this publication in new window or tab >>The Lysekil Wave Power Project: Status Update
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2008 (English)Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-97846 (URN)
Available from: 2008-11-21 Created: 2008-11-21 Last updated: 2014-04-29Bibliographically approved
7. On the Physics and Economics of Renewable Electric Energy Sources -- part I utilization
Open this publication in new window or tab >>On the Physics and Economics of Renewable Electric Energy Sources -- part I utilization
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2008 (English)Conference paper, Published paper (Refereed)
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:uu:diva-97847 (URN)
Conference
??
Available from: 2008-11-21 Created: 2008-11-21 Last updated: 2016-04-12Bibliographically approved
8. On the Physics and Economics of Renewable Electric Energy Sources -- part II engineering
Open this publication in new window or tab >>On the Physics and Economics of Renewable Electric Energy Sources -- part II engineering
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2008 (English)Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-97848 (URN)
Conference
??
Available from: 2008-11-21 Created: 2008-11-21 Last updated: 2016-04-13Bibliographically approved
9. Influence of Generator Damping on Peak Power and Variance of Power for a Direct Drive Wave Energy Converter
Open this publication in new window or tab >>Influence of Generator Damping on Peak Power and Variance of Power for a Direct Drive Wave Energy Converter
2008 (English)In: Journal of Offshore Mechanics and Arctic Engineering-Transactions of The Asme, ISSN 0892-7219, E-ISSN 1528-896X, Vol. 130, no 3, p. 031003-Article in journal (Refereed) Published
Abstract [en]

The first offshore prototype of a wave energy converter system has been launched off the Swedish west coast. The concept is based on a point absorber directly coupled to a linear generator located on the ocean floor. The wave energy converter is part of a research project that will study the electric system of ten units forming a small farm of wave power plants as they are linked and connected to an electric grid. A full scale farm will consist of a large number of interconnected units. The chosen direct drive system reduces the mechanical complexity of the converter but has repercussions on the electric system. The output from the generator will vary with the speed of the point absorber, leading to large fluctuations of power on the second scale. This has implications on both the individual generator and on the system as a whole. The hydrodynamic behavior of the point absorber depends, to a large extent, on the damping of the generator. The damping, in turn, can be remotely controlled by changing the load resistance. It has previously been shown that this has a large influence on the power absorbed by the wave energy converter. This paper investigates the peak power, the translator speed, and the variance of the power at different sea states and for different levels of damping. The peak power has an impact on the design of the generator and the required ability, for a single unit, to handle electric overloads. The momentum of the translator is directly proportional to its speed. The speed is thus important for the design of the end stop. The variance of the power of one unit will have an impact on the farm system behavior. The study is based on two and a half months of experimental measurements on the prototype wave energy converter and a wave measurement buoy. The aim is to analyze whether load control strategies may influence the dimensioning criteria for the electric system and the generator. The results are compared to previously investigated relationships between the absorbed mean power and the load resistance as a function of sea state. In the study, it was found that the maximum power is approximately proportional to the average power, while the maximum translator speed and standard deviation decrease as the damping factor is increased.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-97849 (URN)10.1115/1.2905032 (DOI)000257795900003 ()
Available from: 2008-11-21 Created: 2008-11-21 Last updated: 2017-12-14Bibliographically approved
10. Wave power absorption: Experiments in open sea and simulation
Open this publication in new window or tab >>Wave power absorption: Experiments in open sea and simulation
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2007 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 102, no 8, p. 084910-084910-5Article in journal (Refereed) Published
Abstract [en]

A full scale prototype of a wave power plant based on a direct drive linear generator driven by a point absorber has been installed at the west coast of Sweden. In this paper, experimentally collected data of energy absorption for different electrical loads are used to verify a model of the wave power plant including the interactions of wave, buoy, generator, and external load circuit. The wave-buoy interaction is modeled with linear potential wave theory. The generator is modeled as a nonlinear mechanical damping function that is dependent on piston velocity and electric load. The results show good agreement between experiments and simulations. Potential wave theory is well suited for the modeling of a point absorber in normal operation and for the design of future converters. Moreover, the simulations are fast, which opens up for simulations of wave farms.

Keywords
Hydroelectric, hydrothermal, geothermal and wind power, Ocean energy extraction, Ocean waves and oscillations
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-95684 (URN)10.1063/1.2801002 (DOI)000250589300146 ()
Available from: 2007-03-23 Created: 2007-03-23 Last updated: 2017-12-14Bibliographically approved
11. Wave energy conversion system -– experimental results from offshore operation
Open this publication in new window or tab >>Wave energy conversion system -– experimental results from offshore operation
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In: IEEE Journal of Oceanic EngineeringArticle in journal (Refereed) Accepted
Identifiers
urn:nbn:se:uu:diva-97854 (URN)
Available from: 2008-11-21 Created: 2008-11-21Bibliographically approved
12. Power Absorption of a Wave Energy Converter
Open this publication in new window or tab >>Power Absorption of a Wave Energy Converter
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In: IEEE Journal of Oceanic EngineeringArticle in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-97851 (URN)
Available from: 2008-11-21 Created: 2008-11-21Bibliographically approved
13. Wave Power Absorption as a Function of Water Level and Wave Height: Theory and Experiment
Open this publication in new window or tab >>Wave Power Absorption as a Function of Water Level and Wave Height: Theory and Experiment
2010 (English)In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 35, no 3, p. 558-564Article in journal (Refereed) Published
Abstract [en]

This paper investigates the sensitivity of a wave power system to variations in still water levels and significant wave heights. The system consists of a floating point absorber connected to a linear generator on the seabed. Changing still water levels are expected to affect the power absorption, since they will displace the equilibrium position for the generator translator. Similarly, changing significant wave heights will affect the rate at which the translator leaves the stator. Both these effects will in some cases result in a smaller active area of the stator. A theoretical expression to describe this effect is derived, and compared to measured experimental values for the wave energy converter at the Lysekil research site. During the time of measurements, the still water levels at the site were in the range of [-0.70 m, +0.46 m], and the significant wave heights in the range of [0 m, 2.7 m]. The experimental values exhibit characteristics similar to those of the theoretical expression, especially with changing significant wave heights.

Keywords
Energy capture, experimental results, linear generator, power absorption, wave power
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-97852 (URN)10.1109/JOE.2010.2052692 (DOI)000283226500008 ()
Available from: 2012-01-09 Created: 2008-11-21 Last updated: 2017-12-14Bibliographically approved
14. Offshore experiments on a direct-driven Wave Energy Converter
Open this publication in new window or tab >>Offshore experiments on a direct-driven Wave Energy Converter
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2007 (English)Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-14172 (URN)
Conference
Proceedings of the 7th European Wave and Tidal Energy Conference, 11-13 September 2007, Porto, Portugal.
Available from: 2008-04-25 Created: 2008-04-25 Last updated: 2016-04-22
15. Measuring air gap width of permanent magnet linear generators using search coil sensor
Open this publication in new window or tab >>Measuring air gap width of permanent magnet linear generators using search coil sensor
2007 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 2, p. 024518-Article in journal (Refereed) Published
Abstract [en]

A concept for a wave power plant is being developed at the Centre for Renewable Electric Energy Conversion at the A˚ngström Laboratory at Uppsala University. The concept is based on a permanent magnet linear generator placed on the seabed, directly driven by a surface following buoy. Critical for the survival of the generator is that the air gap between the moving and static parts of the generator is constantly fixed at the designed width to prevent the moving and static parts from connecting during operation. This paper shows the design and evaluation of an inductive sensor for measuring the air gap width during generator operation. In order to survive during years on the seafloor inside the wave power plants, the sensor has deliberately been chosen to be a passive component, as well as robust and compact. A coil etched on a printed circuit board, i.e., a search coil, was the chosen basis for the sensor. The sensor has been tested on an existing test rig of a wave power plant and the results have been compared with finite element simulations.The results show that a search coil magnetic sensor etched on a printed circuit board is a suitable concept for measuring the air gap width. Experimentally measured and theoretically calculated sensor signals show very good agreement. The setup has a sensitivity of +/-0.4 mm in the range of 4-9.5 mm air gap. The potential for future improvements of the sensitivity is considerable.

Keywords
High-current and high-voltage technology: power systems; power transmission lines and cables, Electric motors, Spatial dimensions, Sensors ; remote sensing, Finite-element and Galerkin methods
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-94990 (URN)10.1063/1.2403964 (DOI)000243890800148 ()
Available from: 2006-10-20 Created: 2006-10-20 Last updated: 2017-12-14Bibliographically approved
16. Wave Climate off the Swedish West Coast
Open this publication in new window or tab >>Wave Climate off the Swedish West Coast
2009 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 34, no 6, p. 1600-1606Article in journal (Refereed) Published
Abstract [en]

This paper presents and discusses the wave climate off the Swedish west coast It is based on 8 years (1997-2004) of wave data from 13 sites, nearshore and offshore, in the Skagerrak and Kattegat. The data is a product of the WAM and SWAN wave models calibrated at one site by a wave measurement buoy. It is found that the average energy flux is approximately 5.2 kW/m in the offshore Skagerrak, 2.8 kW/m in the nearshore Skagerrak, and 2.4 kW/m in the Kattegat. One of the studied sites, i.e. site 9, is the location of a wave energy research site run by the Centre for Renewable Electric Energy Conversion at Uppsala University. This site has had a wave power plant installed since the spring of 2006, and another seven are planned to be installed during 2008. Wave energy as a renewable energy source was the driving interest that led to this study and the results are briefly discussed from this perspective.

Keywords
Wave climate, Wave power, Sea state, Extreme waves, Skagerrak, Kattegat
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-97856 (URN)10.1016/j.renene.2008.11.016 (DOI)000264306500024 ()
Available from: 2008-11-21 Created: 2008-11-21 Last updated: 2017-12-14Bibliographically approved

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