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Artificial reef effect and fouling impacts on offshore wave power foundations and buoys: a pilot study
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2009 (English)In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 82, no 3, 426-432 p.Article in journal (Refereed) Published
Abstract [en]

Little is known about the effects of offshore energy installations on the marine environment, and further research could assist in minimizing environmental risks as well as in enhancing potential positive effects on the marine environment. While biofouling on marine energy conversion devices on one hand has the potential to be an engineering concern, these structures can also affect biodiversity by functioning as artificial reefs. The Lysekil Project is a test park for wave power located at the Swedish west coast. Here, buoys acting as point absorbers on the surface are connected to generators anchored on concrete foundations on the seabed. In this study we investigated the colonisation of foundations by invertebrates and fish, as well as fouling assemblages on buoys. We examined the influence of surface orientation of the wave power foundations on epibenthic colonisation, and made observations of habitat use by fish and crustaceans during three years of submergence. We also examined fouling assemblages on buoys and calculated the effects of biofouling on the energy absorption of the wave power buoys. On foundations we demonstrated a succession in colonisation over time with a higher degree of coverage on vertical surfaces. Buoys were dominated by the blue mussel Mytilus edulis. Calculations indicated that biofouling have no significant effect in the energy absorption on a buoy working as a point absorber. This study is the first structured investigation on marine organisms associated with wave power devices

Place, publisher, year, edition, pages
2009. Vol. 82, no 3, 426-432 p.
Keyword [en]
biodiversity, benthos, fish, shellfish, renewable energy, wave power, Sweden
National Category
Biological Sciences Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-107217DOI: 10.1016/j.ecss.2009.02.009ISI: 000265573400007OAI: oai:DiVA.org:uu-107217DiVA: diva2:228337
Available from: 2009-07-29 Created: 2009-07-29 Last updated: 2016-04-18Bibliographically approved
In thesis
1. Wave energy conversion and the marine environment: Colonization patterns and habitat dynamics
Open this publication in new window or tab >>Wave energy conversion and the marine environment: Colonization patterns and habitat dynamics
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A wave energy park has been established on the Swedish west coast outside Lysekil and pioneer work about its interactions with the marine environment has been conducted. So far, little is known about the effects of offshore energy installations on the marine environment, and this thesis assists in minimizing environmental risks as well as in enhancing potential positive effects on the marine environment. The Lysekil research site is situated about two kilometres offshore and has been under development since 2005. During this time 26 “environmental devices”, without generators, consisting of a steel buoy attached via a wire to a foundation on 25 m depth have been placed out for ecological studies on macrofauna in surrounding sediments and on colonization of the foundations and the buoys. Sediment samples to examine macrofauna in the seabed have been taken during five seasons. Biomass, abundance and diversity of infauna in the test site were generally low, but higher than in a nearby control site. The species composition was typical for the area and depth.

In addition to sediment analysis, the effect of wave power concrete foundations on the marine environment has been investigated by scuba diving. The surface orientation and its effect on colonization by sessile organisms was examined on the first five foundations, placed out in 2005, and observations of habitat use by fish and crustaceans were made. The results show a succession of colonization over time (three years of investigation) with a higher cover by sessile organisms on vertical surfaces. Mobile fauna abundance on and around the foundations was generally low.

Three months after the deployment of the 21 new foundations in 2007, assemblages of mobile organisms were examined visually. Also here, mobile species exhibit a low density, but still higher than on surrounding soft bottoms. The edible crab used artificial holes in the foundations frequently. The foundations were placed in two different clusters, north and south, and the degree to which early recruits covered the foundations and the succession of epibenthic communities were documented during two years. Sessile organisms colonized the northern foundations more rapidly, producing a higher diversity which suggests that the placement of wave energy devices affects colonization patterns.

Biofouling on buoys was examined and blue mussels, Mytilus edulis, dominated with a cover about 90%. Wave exposed buoys were particularly favoured by M. edulis which there had a higher biomass and larger shells compared to those on sheltered buoys. Biofouling on wave power buoys, independent whether these had a cylindrical or toroidal shape, was insufficient to markedly affect their energy production.

Finally, the thesis incorporates a review describing wave power projects in general pointing out the need of future research on for instance no-take zones, marine bioacoustics and electromagnetic fields. The main conclusions are that large-scale renewable wave energy conversion will cause ecological impact primarily by adding new hard substrate to an area but not by harming organisms or decreasing biodiversity within wave power parks.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 50 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 663
Keyword
artificial reefs, benthos, biodiversity, biofouling, colonization, environmental impact, fish, shellfish, Mytilus edulis, renewable energy, wave power
National Category
Biological Sciences
Research subject
Animal Ecology
Identifiers
urn:nbn:se:uu:diva-107193 (URN)978-91-554-7581-9 (ISBN)
Public defence
2009-10-02, Friessalen, Norbyvägen 14, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2009-09-03 Created: 2009-07-27 Last updated: 2016-05-02Bibliographically approved
2. Hydrodynamic Modelling for a Point Absorbing Wave Energy Converter
Open this publication in new window or tab >>Hydrodynamic Modelling for a Point Absorbing Wave Energy Converter
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Surface gravity waves in the world’s oceans contain a renewable source of free power on the order of terawatts that has to this date not been commercially utilized. The division of Electricity at Uppsala University is developing a technology to harvest this energy. The technology is a point absorber type wave energy converter based on a direct-driven linear generator placed on the sea bed connected via a line to a buoy on the surface.

The work in this thesis is focused mainly on the energy transport of ocean waves and on increasing the transfer of energy from the waves to the generator and load. Potential linear wave theory is used to describe the ocean waves and to derive the hydrodynamic forces that are exerted on the buoy. Expressions for the energy transport in polychromatic waves travelling over waters of finite depth are derived and extracted from measured time series of wave elevation collected at the Lysekil test site. The results are compared to existing solutions that uses the simpler deep water approximation. A Two-Body system wave energy converter model tuned to resonance in Swedish west coast sea states is developed based on the Lysekil project concept. The first indicative results are derived by using a linear resistive load. The concept is further extended by a coupled hydrodynamic and electromagnetic model with two more realistic non-linear load conditions.

Results show that the use of the deep water approximation gives a too low energy transport in the time averaged as well as in the total instantaneous energy transport. Around the resonance frequency, a Two-Body System gives a power capture ratio of up to 80 percent. For more energetic sea states the power capture ratio decreases rapidly, indicating a smoother power output. The currents in the generator when using the Two-Body system is shown to be more evenly distributed compared to the conventional system, indicating a better utilization of the electrical equipment. Although the resonant nature of the system makes it sensitive to the shape of the wave spectrum, results indicate a threefold increase in annual power production compared to the conventional system.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 91 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 878
Keyword
Ocean wave energy, Point absorber, Wave energy converter, Wave energy transport, Polychromatic wave, Linear generator, Resonance, Finite depth, Modelling
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Marine Engineering Oceanography, Hydrology, Water Resources
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-160319 (URN)978-91-554-8214-5 (ISBN)
Public defence
2011-12-09, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2011-11-17 Created: 2011-10-21 Last updated: 2011-11-23Bibliographically approved

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