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Adaptation of wave power plants to regions with high tides
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The wave energy converter (WEC) developed at Uppsala University is based on the concept of a heaving point absorber with a linear generator placed on the seafloor. The translator inside the generator oscillates in a linear fashion and is connected via a steel wire to a point absorbing buoy. The power production from this device is optimal when the translator’s oscillations are centered with respect to the stator. However, due to the tides, the mean translator position may shift towards the upper or lower limits of the generator’s stroke length, thereby affecting the power production. This effect will be severe if the WEC operates in an area characterized by a high tidal range. The translator may be stuck at the top or rest at the bottom of the generator for a considerable amount of time daily.

One of the solutions to this problem is to develop a compensator that is able to adjust the length of the connecting line. With an estimated weight of 10 tonnes of the connecting line and the translator, the use of a pocket wheel wound with steel chain was deemed suitable. Not being connected to an external power supply, the device needs a alternative local power supply to charge batteries that run the system. A hybrid system of solar photovoltaics (PV) and a small WEC was proposed to power the device and, based on the simulations for two different sea states, the hybrid system was found suitable for powering the device all year round. The experimental work carried out in the lab environment has shown that the compensator was able to lift the estimated load of the translator and to position the chain so that it follows the variations in the sea level from meteorological websites.

The second part of the thesis is a study on the wave energy potential in the Nordic synchronous grid. A model for the allocation of wave farms for four energy scenarios was developed, linearly weighted to the intensity of the wave energy flux. As an extension to this study, a net load variability study for a highly or a fully renewable Nordic power system was conducted. It involved four different intermittent renewable energy (IRE) sources: solar PV, wind, tidal power, and wave. The study shows that an optimal combination of IRE sources to replace fossil fuels and nuclear energy is possible from the perspective of net load variability.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 53
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1795
Keywords [en]
Wave energy, Tides, Wave Hub, Lysekil research site, Control system, Tidal compensator, Wave energy converter.
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
URN: urn:nbn:se:uu:diva-381169ISBN: 978-91-513-0627-8 (print)OAI: oai:DiVA.org:uu-381169DiVA, id: diva2:1302534
Public defence
2019-05-22, Room 2001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Available from: 2019-04-26 Created: 2019-04-05 Last updated: 2019-06-17
List of papers
1. Wave Energy Research at Uppsala University and The Lysekil Research Site, Sweden: A Status Update
Open this publication in new window or tab >>Wave Energy Research at Uppsala University and The Lysekil Research Site, Sweden: A Status Update
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2015 (English)Conference paper, Published paper (Refereed)
Abstract [en]

This paper provides a summarized status update ofthe Lysekil wave power project. The Lysekil project is coordinatedby the Div. of Electricity, Uppsala University since 2002, with theobjective to develop full-scale wave power converters (WEC). Theconcept is based on a linear synchronous generator (anchored tothe seabed) driven by a heaving point absorber. This WEC has nogearbox or other mechanical or hydraulic conversion systems,resulting in a simpler and robust power plant. Since 2006, 12 suchWECs have been build and tested at the research site located atthe west coast of Sweden. The last update includes a new andextended project permit, deployment of a new marine substation,tests of several concepts of heaving buoys, grid connection,improved measuring station, improved modelling of wave powerfarms, implementation of remote operated vehicles forunderwater cable connection, and comprehensive environmentalmonitoring studies.

Keywords
Wave energy, point absorber, experiments, arrays, generators, ROVs
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Ocean and River Engineering
Identifiers
urn:nbn:se:uu:diva-265218 (URN)
Conference
Proceedings of the 11th European Wave and Tidal Energy Conference. Nantes, France, September 2015
Available from: 2015-10-26 Created: 2015-10-26 Last updated: 2019-08-19Bibliographically approved
2. Tidal Effect Compensation System Design for High Range Sea Level Variations
Open this publication in new window or tab >>Tidal Effect Compensation System Design for High Range Sea Level Variations
2015 (English)Conference paper, Poster (with or without abstract) (Refereed)
Abstract [en]

The working principle of the wave energy converter (WEC) from Uppsala University is a heaving point absorber with directly driven linear generator placed on the seabed. The heave motion of the buoy is transmitted to the generator via a steel cable. When tides occur, the sea level changes, and thus making the WEC works below optimal condition. This system is designed so that the WEC is able to work at sea level variation up to 8 meters. A compensation system is designed to continuously make the WEC work in its optimal condition even at different sea levels. We present a mechanical system and its control algorithm that monitor and control the length of the connecting line. The connecting line is consist of a steel wire and a steel chain connected together. The mechanical part of the system is the winch that retracts or releases the steel chain that connects the translator and the buoy at the water surface. The rotation of the winch is controlled by a motor with the help of microcontrollers and several sensors for accuracy and feedback. The result from simulation showed that the system works fine. The approach of compensating the wire length connecting the buoy and the translator allow more flexibility to WEC to work in the area with high sea level variation.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-286598 (URN)
Conference
Proceedings of the 11th European Wave and Tidal Energy Conference 6-11th Sept 2015, Nantes, France
Available from: 2016-04-21 Created: 2016-04-21 Last updated: 2019-04-05
3. Small-Scale Renewable Energy Converters for Battery Charging
Open this publication in new window or tab >>Small-Scale Renewable Energy Converters for Battery Charging
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2018 (English)In: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 6, no 1, article id 26Article in journal (Refereed) Published
Abstract [en]

This paper presents two wave energy concepts for small-scale electricity generation. In the presented case, these concepts are installed on the buoy of a heaving, point-absorbing wave energy converter (WEC) for large scale electricity production. In the studied WEC, developed by Uppsala University, small-scale electricity generation in the buoy is needed to power a tidal compensating system designed to increase the performance of the WEC in areas with high tides. The two considered and modeled concepts are an oscillating water column (OWC) and a heaving point absorber. The results indicate that the OWC is too small for the task and does not produce enough energy. On the other hand, the results show that a hybrid system composed of a small heaving point absorber combined with a solar energy system would be able to provide a requested minimum power of around 37.7W on average year around. The WEC and solar panel complement each other, as the WEC produces enough energy by itself during wintertime (but not in the summer), while the solar panel produces enough energy in the summer (but not in the winter).

Place, publisher, year, edition, pages
MDPI, 2018
Keywords
small wave energy converter, oscillating water column, heaving point absorber
National Category
Energy Engineering
Identifiers
urn:nbn:se:uu:diva-357765 (URN)10.3390/jmse6010026 (DOI)000428558900025 ()
Funder
Swedish Energy AgencySwedish Research Council, 2015-04657ÅForsk (Ångpanneföreningen's Foundation for Research and Development)StandUpCarl Tryggers foundation
Available from: 2018-08-22 Created: 2018-08-22 Last updated: 2019-04-05Bibliographically approved
4. Control Strategy for a Tidal Compensation System for Wave Energy Converter Device
Open this publication in new window or tab >>Control Strategy for a Tidal Compensation System for Wave Energy Converter Device
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2018 (English)Conference paper, Oral presentation with published abstract (Refereed)
National Category
Ocean and River Engineering Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-363349 (URN)978-1-880653-87-6 (ISBN)
Conference
The 28th International Ocean and Polar Engineering Conference, 10-15 June, Sapporo, Japan
Available from: 2018-10-17 Created: 2018-10-17 Last updated: 2019-04-05Bibliographically approved
5. A remotely controlled sea level compensation system for wave energy converters
Open this publication in new window or tab >>A remotely controlled sea level compensation system for wave energy converters
2019 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, no 10, article id 1946Article in journal (Refereed) Published
Abstract [en]

The working principle of the wave energy converter (WEC) developed at Uppsala University (UU) is based on a heaving point absorber with a linear generator. The generator is placed on the seafloor and is connected via a steel wire to a buoy floating on the surface of the sea. The generator produces optimal power when the translator's oscillations are centered with respect to the stator. However, due to the tides or other changes in sea level, the translator's oscillations may shift towards the upper or lower limit of the generator's stroke length, resulting in a limited stroke and a consequent reduction in power production. A compensator has been designed and developed in order to keep the generator's translator centered, thus compensating for sea level variations. This paper presents experimental tests of the compensator in a lab environment. The wire adjustments are based on online sea level data obtained from the Swedish Meteorological and Hydrological Institute (SMHI). The objective of the study was to evaluate and optimize the control and communication system of the device. As the device will be self-powered with solar and wave energy, the paper also includes estimations of the power consumption and a control strategy to minimize the energy requirements of the whole system. The application of the device in a location with high tides, such as Wave Hub, was analyzed based on offline tidal data. The results show that the compensator can minimize the negative effects of sea level variations on the power production at the WEC. Although the wave energy concept of UU is used in this study, the developed system is also applicable to other WECs for which the line length between seabed and surface needs to be adjusted.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
wave energy converter, tidal compensation, control system, tides, Wave Hub
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-381166 (URN)10.3390/en12101946 (DOI)000471016700125 ()
Funder
Swedish Energy Agency, 2016-002062
Available from: 2019-04-05 Created: 2019-04-05 Last updated: 2019-08-06Bibliographically approved
6. Wave energy potential and 1-50 TWh scenarios for the Nordic synchronous grid
Open this publication in new window or tab >>Wave energy potential and 1-50 TWh scenarios for the Nordic synchronous grid
2017 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 101, p. 462-466Article in journal (Refereed) Published
Abstract [en]

This study estimates the wave energy potential along the coasts of the Nordic countries with the Nordicsynchronous grid as a chosen boundary. A model for wave farm allocation was developed and applied to achieve annual energy production targets of 1 TWh, 3 TWh, 10 TWh and 50 TWh. The study is based on 10 years of data, from 2005 to 2014, from the European Center for Medium-Range Weather Forecasts. Data from a total of 728 coordinate points along the Nordic countries, with a 0.125° x 0.125° spatial resolution, were considered. An algorithm was developed to generate the scenarios, to estimate the installed capacity of wave farms at different locations along the coasts, and to measure the physical space required by the farms. This analysis of the four energy target scenarios resulted in a required installed capacity of 337 MW, 1.02 GW, 3.42 GW and 17.09 GW, covering a stretch of the total coast of 0.4, 1.2, 3.8 and 18.9% respectively. The total annual wave energy resource for the Nordic countries is determined at 590 TWh, most of which is available along the Norwegian coast.

Keywords
wave energy, wave farm, installed power, scenarios, Nordic synchronous grid
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Environmental Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-307177 (URN)10.1016/j.renene.2016.09.004 (DOI)000388775700044 ()
Funder
Swedish Energy AgencyÅForsk (Ångpanneföreningen's Foundation for Research and Development)StandUpCarl Tryggers foundation
Available from: 2016-11-10 Created: 2016-11-10 Last updated: 2019-04-05Bibliographically approved
7. Net load variability in Nordic countries with a highly or fully renewable power system
Open this publication in new window or tab >>Net load variability in Nordic countries with a highly or fully renewable power system
Show others...
2016 (English)In: Nature Energy, ISSN 2058-7546, Vol. 1, p. 1-8, article id 16175Article in journal (Refereed) Published
Abstract [en]

Increasing the share of intermittent renewable energy (IRE) resources such as solar, wind, wave and tidal energy in a power system poses a challenge in terms of increased net load variability. Fully renewable power systems have previously been analysed, but more systematic analyses are needed that explore the effect of different IRE mixes on system-wide variability across different timescales and the optimal combinations of IRE for reducing variability on a given timescale. Here we investigate these questions for the Nordic power system. We show that the optimal mix of IRE is dependent on the frequency band considered. Long-term (>4 months) and short-term (<2 days) fluctuations can be similar to today’s, even for a fully renewable system. However, fluctuations with periods in between will inevitably increase significantly. This study indicates that, from a variability point of view, a fossil- and nuclear-free Nordic power system is feasible if properly balanced by hydropower.

National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-302836 (URN)10.1038/NENERGY.2016.175 (DOI)000394793000001 ()
Funder
StandUpStandUp for Wind
Available from: 2016-09-11 Created: 2016-09-11 Last updated: 2019-04-05

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Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
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Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
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  • asciidoc
  • rtf