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Resource characterization and variability studies for marine current power
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Uppsala University.
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 [en]
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: urn:nbn:se:uu:diva-319033ISBN: 978-91-554-9881-8 (print)OAI: oai:DiVA.org:uu-319033DiVA: diva2:1086925
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
List of papers
1. Measurements of tidal current velocities in the Folda fjord, Norway, with the use of a vessel mounted ADCP
Open this publication in new window or tab >>Measurements of tidal current velocities in the Folda fjord, Norway, with the use of a vessel mounted ADCP
2014 (English)In: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 8A: Ocean Engineering, 2014Conference paper, Presentation (Refereed)
Abstract [en]

Measurements of tidal current water velocities is an important first step in evaluating the potential for a tidal site to be used as a renewable energy resource. For this reason, on site measurements are performed at the inlet of a fjord situated at the coast of Norway. The site has an average width of 580 m and adepth of 10-15 m which is narrow and shallow enough to give rise to water velocities that can be of use for energy conversion. With the use of an Acoustic Doppler Current Profiler (ADCP) cross-section measurements are conducted along four transects. The measurements covered flood and ebb currents around one tide and the data give a first approximation of the magnitude and distribution of the flow field. Depth averaged mean current velocities are calculated along the transects for horizontal bins with sizes in the order of 50 x 50 m. Maximum mean velocity for the flood currents were 1.31 m/s and 1.46 m/s for the ebb currents. The measurements show that even a small amount of data can give an indication of the potential and characteristics ofthe site.

Keyword
Acoustic Doppler Current Profiler (ADCP), tidal energy resource
National Category
Marine Engineering Ocean and River Engineering Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-230659 (URN)000363498500053 ()978-0-7918-4550-9 (ISBN)
Conference
33rd International Conference on Ocean, Offshore and Arctic Engineering (OMAE2014), San Francisco, California, USA, June 8-13, 2014
Available from: 2014-08-27 Created: 2014-08-27 Last updated: 2017-04-04Bibliographically approved
2. Tidal resource characterization in the Folda Fjord, Norway
Open this publication in new window or tab >>Tidal resource characterization in the Folda Fjord, Norway
2016 (English)In: International Journal of Marine Energy, ISSN 2214-1669, Vol. 13, 27-44 p.Article in journal (Refereed) Published
Abstract [en]

For tidal-stream energy industry to be fully realized, lower velocity sites and fjords should be developed. Finding new prospective sites for in-stream energy extraction from tidal currents is an area of ongoing research. In this paper, the tidal flow at a fjord inlet has been characterized using acoustic Doppler current profiler (ADCP) measurements. This work is based on two survey measurement techniques: transect measurements to map the spatial variability, and seabed measurements to map the temporal variability. The data was analyzed in terms of characterizing metrics, to ensure they are comparable with other resource assessments. Results show that currents exceed 1 m/s for 38% of the time with peak currents of 2.06 m/s at hub height (middle of the water column) and the directional asymmetry is less than 1° between ebb and flood, indicating a truly bi-directional flow. A simple prediction model is proposed which allows peak current speeds to be accurately predicted in the channel center from tidal range data using a linear relationship. The relationship is shown to be strong, with a correlation coefficient of 0.98 at hub height, and a standard variation typically less than 10 cm/s. Furthermore, it is show that a minimum of 9 days of measurements are required to set up the model, although it takes 29 days to reduce the error in peak speed to less than 1%. However, the error is expected to vary depending on where in the monthly tidal cycle the survey begins, it is thus recommended to measure around spring tide if the measurement period is short.

Keyword
Tidal resource assessment, ADCP, Characterizing metrics
National Category
Engineering and Technology Ocean and River Engineering Oceanography, Hydrology, Water Resources
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-266674 (URN)10.1016/j.ijome.2016.01.001 (DOI)000381687600003 ()
Funder
StandUpCarl Tryggers foundation
Available from: 2015-11-10 Created: 2015-11-10 Last updated: 2017-04-04Bibliographically approved
3. The Söderfors Project: Experimental Hydrokinetic Power Station Deployment and First Results
Open this publication in new window or tab >>The Söderfors Project: Experimental Hydrokinetic Power Station Deployment and First Results
Show others...
2013 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The Division of Electricity at Uppsala University recently deployed an experimental hydrokinetic power station for in-stream experiments at a site in a river. This paper briefly describes the deployment process and reports some initial results from measurements made at the test site.

Keyword
Marine Current Power, Renewable energy, Söderfors, Strömkraft, Förnybar energi, Söderfors
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-209220 (URN)
Conference
10th European Wave and Tidal Energy Conference (EWTEC), 2-5 september, 2013, Aalborg, Denmark
Projects
Marine Current Power
Funder
StandUpSwedish Research Council, 621-2009-4946
Available from: 2013-10-15 Created: 2013-10-15 Last updated: 2017-04-04Bibliographically approved
4. Studying the Wake of a Marine Current Turbine Using an Acoustic Doppler Current Profiler
Open this publication in new window or tab >>Studying the Wake of a Marine Current Turbine Using an Acoustic Doppler Current Profiler
2015 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Wake characteristics of marine current turbines are of significant importance to the development of the marine current power source. Turbine wake recovery determines spacing of turbines in arrays, and environmental impact on e.g. the seabed is heavily influenced by wake behaviour. The majority of previous studies on wakes has been performed on flow-aligned (horizontal) axis turbines and mainly carried out as scale model experiments or numerical simulations.

This paper describes the performance of wake measurements at the Söderfors test site, where an experimental marine current power station is operated in a river. The turbine is of the cross-flow (vertical) axis type, and the measurements are performed using an Acoustic Doppler Current Profiler (ADCP) towed on the surface by a boat. Positioning data is taken from a high-accuracy Global Navigation Satellite System. The paper discusses various aspects of the methodology employed and provides examples of taken measurements.

National Category
Energy Engineering Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-265358 (URN)
Conference
11th European Wave and Tidal Energy Conference, EWTEC15, 6-11 September 2015, Nantes, France
Available from: 2015-10-27 Created: 2015-10-27 Last updated: 2017-04-04Bibliographically approved
5. Observation of cavitating flow using multibeam and dual-beam sonar systems: A comparison of wake strength caused by propeller vs waterjet thrusted vessels. In a marine renewable energy perspective (Part-a)
Open this publication in new window or tab >>Observation of cavitating flow using multibeam and dual-beam sonar systems: A comparison of wake strength caused by propeller vs waterjet thrusted vessels. In a marine renewable energy perspective (Part-a)
(English)In: Article in journal (Refereed) Submitted
Abstract
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-307239 (URN)
Available from: 2016-11-11 Created: 2016-11-11 Last updated: 2017-04-04
6. Variability Assessment and Forecasting of Renewables: A Review for Solar, Wind, Wave and Tidal Resources
Open this publication in new window or tab >>Variability Assessment and Forecasting of Renewables: A Review for Solar, Wind, Wave and Tidal Resources
Show others...
2015 (English)In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 44, 356-375 p.Article in journal (Refereed) Published
National Category
Energy Engineering Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity; Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-225870 (URN)10.1016/j.rser.2014.12.019 (DOI)000351324300025 ()
Available from: 2014-06-09 Created: 2014-06-09 Last updated: 2017-04-04
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, 1-8 p., 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 ()
Available from: 2016-09-11 Created: 2016-09-11 Last updated: 2017-04-04Bibliographically approved
8. Tidal current phasing along the coast of Norway
Open this publication in new window or tab >>Tidal current phasing along the coast of Norway
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.

Keyword
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:nbn:se:uu:diva-307495 (URN)
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

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