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Tidal current phasing along the coast of Norway
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2016 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Tidal currents provide an intermittent source of renewable energy. A high degree of intermittency is unfavorable in the existing power system. However, by aggregating tidal power from sites with variable tidal phase a more firm power outpu tmay be achieved. In this paper, the tidal current phasing between 114 potential tidal energy sites along the Norwegian coast is investigated. Time series of tidal currents are generated with a model that considers the variation in current strength due to the variability in the semi-diurnal tidal cycle (spring to neap, flood to ebb, first to second daily tide etc.). From these, available kinetic energy in the natural flow is calculated. A constant conversion rate is then applied to give the power output at each site. Three scenarios, with varying number of sites and energy extraction, are investigated. The variability in each scenario is quantified on different time scales by filtering the aggregated power and calculate standard deviation and step change. It is found that the variability can be lowered by choosing sites with an advantageous time lag and limit the power output from the most energetic sites. As expected, smoothing is most distinct on short time scales.

Place, publisher, year, edition, pages
2016.
Keyword [en]
Tidal energy, tidal phasing, variability optimization, significant impact factor, model scenarios
National Category
Ocean and River Engineering Marine Engineering Oceanography, Hydrology, Water Resources
Identifiers
URN: urn:nbn:se:uu:diva-307495OAI: oai:DiVA.org:uu-307495DiVA: diva2:1056146
Conference
3rd International Asian Wave and Tidal Energy Conference (AWTEC), Singapore 24-28 oct, 2016
Funder
StandUpÅForsk (Ångpanneföreningen's Foundation for Research and Development), 16-196
Available from: 2016-12-14 Created: 2016-11-16 Last updated: 2017-04-04
In thesis
1. Resource characterization and variability studies for marine current power
Open this publication in new window or tab >>Resource characterization and variability studies for marine current power
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Producing electricity from marine renewable resources is a research area that develops continuously. The field of tidal energy is on the edge to progress from the prototype stage to the commercial stage. However, tidal resource characterization, and the effect of tidal turbines on the flow, is still an ongoing research area in which this thesis aims to contribute.

In this thesis, measurements of flow velocities have been performed at three kinds of sites. Firstly, a tidal site has been investigated for its resource potential in a fjord in Norway. Measurements have been performed with an acoustic Doppler current profiler to map the spatial and temporal characteristics of the flow. Results show that currents are in the order of 2 m/s in the center of the channel. Furthermore, the flow is highly bi-directional between ebb and flood flows. The site thus has potential for in-stream energy conversion. Secondly, a river site serves as an experimental site for a marine current energy converter that has been designed at Uppsala University and deployed in Dalälven, Söderfors. The flow rate at the site is regulated by an upstream hydro power plant, making the site suitable for experiments on the performance of the vertical axis turbine in a natural environment. The turbine was run in steady discharge flows and measurements were performed to characterize the extent of the wake. Lastly, at an ocean current site, the effect that transiting ferries may have on submerged devices was investigated. Measurements were conducted with two sonar systems to obtain an underwater view of the wake caused by a propeller and a water jet thruster respectively.

Furthermore, the variability of the intermittent renewable sources wind, solar, wave and tidal energy was investigated for the Nordic countries. All of the sources have distinctly different variability features, which is advantageous when combining power generated from them and introducing it on the electricity grid. Tidal variability is mainly due to four aspects: the tidal regime, the tidal cycle, local bathymetry causing turbulence, asymmetries etc. and weather effects. Models of power output from the four sources was set up and combined in different energy mixes for a “highly renewable” and a “fully renewable” scenario. By separating the resulting power time series into different frequency bands (long-, mid-, mid/short-, and short-term components) it was possible to minimize the variability on different time scales. It was concluded that a wise combination of intermittent renewable sources may lower the variability on short and long time scales, but increase the variability on mid and mid/short time scales.

The tidal power variability in Norway was then investigated separately. The predictability of tidal currents has great advantages when planning electricity availability from tidal farms. However, the continuously varying tide from maximum power output to minimum output several times per day increases the demand for backup power or storage. The phase shift between tidal sites introduces a smoothing effect on hourly basis but the tidal cycle, with spring and neap tide simultaneously in large areas, will inevitably affect the power availability.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 64 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1499
Keyword
Marine current energy, tidal currents, wake, variability, renewable energy, ADCP, flow measurement
National Category
Ocean and River Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-319033 (URN)978-91-554-9881-8 (ISBN)
Public defence
2017-05-31, Häggsalen, Ångströmlaboratoriet, Uppsala, 09:15 (English)
Opponent
Supervisors
Funder
StandUpSwedish Energy AgencyÅForsk (Ångpanneföreningen's Foundation for Research and Development)Carl Tryggers foundation
Available from: 2017-05-05 Created: 2017-04-04 Last updated: 2017-05-08

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