Estimating the ocean currents in the Berlengas – Peniche channel as a contribute for stream energy site assessment, using the Atlantic-Iberian Biscay Irish- Ocean Physics Analysis and Forecast data
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1
MARE - IPLeiria, Portugal
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2
CiTUR - IPLeiria, Portugal
Ocean Energy has the potential to contribute for clean and renewable energy goals in a near future, although much work is in initial or pilot phase the 2014 JRC Ocean Energy Status Report foresees about 40 MW of tidal and 26 MW of wave energy to be installed by 2018. Some of the work to be done is related to site assessment, which is needed in order to quantify the site energy and the possibility to convert some into electrical energy. In Portugal western coast the Berlengas – Peniche channel is a site with enough interest to be considered for tidal stream energy assessment. Some references were made in the past to an amplification effect in the Berlengas region, near to Cabo Carvoeiro – Peniche. Marta-Almeida and Dubert (2006) stated that velocities in this region are relatively higher when compared to other regions of the Portuguese continental shelf. Almeida and Guedes Soares (2015) also mention that “The most prominent feature in the tidal stream energy occurs due to the costal geometry in the region of the Cape Carvoeiro, where semi-diurnal and diurnal tides ellipse amplification occurs, leading to an increasing tidal potential region”. This stream amplification effect in the Berlengas – Peniche channel is evidently related to the local bathymetry, as mentioned by Vasconcelos and Gamboa (2009) because in it has an average depth around 40 m, while in the North direction it increases drastically due to the Nazare Canyon and in the south direction the depth also increases in an average slope of 10m per kilometer.
Energy assessment is generally made by two complementary ways, with direct measurements and with modeling numerical studies. The measurements should be made in a region wide enough and during sufficient time in order to reflect the resource seasonal variability, but sometimes the resources are not enough to allow for such studies. One other issue is that the field trips to make ocean measurements generally occur in good weather and sea conditions, that means low wind and low ocean currents that are not representative for the ocean conditions. This reflection lead to the idea of estimate the ocean currents in the Berlengas – Peniche channel using the Atlantic-Iberian Biscay Irish- Ocean Physics Analysis and Forecast (IBI MFC) data.
The IBI MFC includes high frequency processes to characterize regional scale marine processes, like tidal forcing, surges and high frequency atmospheric forcing, fresh water river discharge, etc. The system is based on a (eddy-resolving) NEMO model application (Madec, 2008) run at 1/36 degree, with horizontal resolution near 2km. It is composed by 3D daily means fields of Temperature, Salinity, Sea Surface Height, Zonal Velocity and Meridional Velocity, as well as by hourly means of surface fields, to obtain a better understanding of the ocean dynamic in the IBI Atlantic waters (Sotillo et al., 2015). The vertical mixing is parameterized according to Umlauf and Burchard (2003) latent sensible heat fluxes, evaporation and surface stress are calculated according to (Large and Yeager, 2004). Solar penetration is parameterized with data from Seawif satellite ocean color imagery. Lateral open boundary data (temperature, salinity, velocities and sea level) are interpolated from the daily outputs complemented by 11 tidal harmonics (M2, S2, N2, K1, O1, Q1, M4, K2, P1, Mf, Mm) according to (Lyard et al., 2006) and (Egbert and Erofeeva, 2002) tidal models solutions.
To validate the approach velocity measurements were used and compared with the model results for the same time and location. In this case the velocity was measured in April 28, 2011 between 11h44m and 15h10m in several points within the Berlengas – Peniche channel with a PASCO Flow Meter PA-2130 at approximately 3 meters depth resulting values between 21 cm/s and 26 cm/s as presented by Cecílio (2011). Consulting the model for the same time and similar location the values presented are between 15 and 22 cm/s which was considered acceptable.
To estimate the ocean currents in the Berlengas – Peniche channel the data from the Atlantic-Iberian Biscay Irish- Ocean Physics Analysis and Forecast was downloaded from the Copernicus web site for the channel region for 2013, 14 and 15 for each hour. From the velocity maps evolution with time it could be seen that the channel presented generally the higher velocity values in the vicinity, but the maximum absolute values for the velocity were always below 100 cm/s. A representative region for the stream current in the channel was chosen, on the area where the maximum values for the velocity were higher, centered on the coordinates 39,389 N and 9,444 E was selected. The values for the absolute velocity were then calculated for that location over the hours of each year, reaching to the following conclusions:
2013: Average=29,1 cm/s, Max=100,5 cm/s, SD=17,6; H30=5463h; H50=2017h; H70=471h
2014: Average=30,3 cm/s, Max= 92,2 cm/s, SD=16,4; H30=5870h; H50=1168h; H70=575h
2015: Average=23,2 cm/s, Max= 94,8 cm/s, SD=14,2; H30=5372h; H50=1696h; H70=290h
Where Average represents the average throughout the year, Max the maximum velocity obtained and SD the standard deviation. The number of hours where velocity is greater than 30cm/s is represented by H30, number of hours wherevelocity is greater than 50cm/s H50, and H70 greater than 70 cm/s.
Has mentioned earlier the velocity is generally below 100 cm/s that is generally considered a low value for extracting energy from the stream. In fact most of the turbines are designed for values above 1 m/s and not below. To collect energy from the stream in this channel low speed turbines should be considered (Shiono et al., 2002) and careful economical calculations should be made, although this results are only a first estimative and can be improved with better resolution calculations and velocity measurements at surface and along the water column. As conclusion of this work we may state that the stream velocity is not enough to advice the development of ocean stream energy projects in the Berlengas – Peniche channel.
Acknowledgements
This work was only possible with the access to the Copernicus Marine Environment Monitoring Service products and services for which the authors are grateful.
References
Marta-Almeida M, Dubert J., 2006. The structure of tides in the Western Iberian region. Continental Shelf Research 26: 385 – 400.
Almeida M.M., Guedes Soares C., 2015. Numerical investigation of the tidal Energy potential in the Portuguese continental shelf. Renewable Energies Offshore – Guedes Soares (Ed.) Taylor & Francis Group, London, ISBN: 978-1-138-02871-5.
Vasconcelos, J and Gamboa, R., 2009. BOP – Berlengas Ocean Power, the possibility for electrical power production from the submarine ocean current water flow in the Berlengas – Peniche channel. Main steps to investigate the BOP production possibility, proceedings of IMMR09 - International Meeting on Marine Resources, Peniche, Portugal.
Cecílio, C. J., 2011. A Energia dos Oceanos ao largo de Peniche, Master Thesis in Energy and Environment – Instituto Politécnico de Leiria, Portugal.
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Keywords:
Ocean energy,
Site assessment,
Surface velocity,
Oceanography,
Stream energy
Conference:
IMMR | International Meeting on Marine Research 2016, Peniche, Portugal, 14 Jul - 15 Jul, 2016.
Presentation Type:
Poster presentation
Topic:
Oceanography and Maritime Technology
Citation:
Gamboa
RM,
Vasconcelos
JV,
Leandro
S and
Maranhão
P
(2016). Estimating the ocean currents in the Berlengas – Peniche channel as a contribute for stream energy site assessment, using the Atlantic-Iberian Biscay Irish- Ocean Physics Analysis and Forecast data.
Front. Mar. Sci.
Conference Abstract:
IMMR | International Meeting on Marine Research 2016.
doi: 10.3389/conf.FMARS.2016.04.00013
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Received:
14 May 2016;
Published Online:
13 Jul 2016.
*
Correspondence:
PhD. Roberto M Gamboa, MARE - IPLeiria, Peniche, I am not in the U.S. or Canada, 2520-641, Portugal, roberto.gamboa@ipleiria.pt