Energy Postgraduate Conference 2013 Resource Assessment of the Agulhas Current to determine Feasibility for Marine Energy Extraction Centre for Renewable.

Energy Postgraduate Conference 2013

Resource Assessment of the Agulhas Current to determine Feasibility for Marine Energy Extraction Centre for Renewable and Sustainable Energy StudiesStellenbosch University

Presenter: Josh ReineckeResearchers: I. Meyer, J. Reinecke & Prof J. L Van Niekerk

Ocean Current Energy Ocean Current Energy around South Africaaround South Africa

Agulhas Current is South Africa’s strongest ocean

current resource

Viability for energy extraction?

• Water mass contribution of the Agulhas Current:– Agulhas Current retroflection – largest source– Mozambique Current– East Madagascar Current

• Poleward flowing Under Current

• The continental shelf narrows between Durban and Port Edward

– causing the current to flow near the shore with a high velocity

– also helps stabilize the Agulhas Current in this region and no regular wide meanderings are present.

• Destabilizing Region: The Natal Bight

– Situated between Durban and Richards Bay

– This area has a wider continental shelf and the shelf’s morphology change destabilizes the current, resulting in infrequent formation of Natal Pulses

Agulhas Current: Agulhas Current: CharacteristicsCharacteristics

} The contributions from these two sources are mostly in the form of eddies or rings

Agulhas Current: Previous Agulhas Current: Previous ResearchResearch

Mean structure of the Agulhas Current presented by Bryden et al (Bryden, et al., 2005)

Velocity structure [cm/s] (Beal & Bryden, 1999)

• Bryden et al (2005) took the variability into account when examining the mean characteristics of the Agulhas Current through the use of composite spectral analysis

• It was concluded in the study that a transport of -69.7 Sv ± 4.3 Sv is achieved by the Agulhas Current at 31o S

Beal and Bryden discovered that the core of the current is situated 20 km from the coastline at the surface and it is 70 km wide

Agulhas Current: Data Agulhas Current: Data AnalysedAnalysed

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Kei Mouth

East London

Port Alfred

Port Edward

Mbashe estuary

Mdumbi estuary

Port Elizabeth

Port St. Johns

Waterfall Bluff

Cape St. Francis

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Cape Morgan%U

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200 m

500 m

1000 m

Eskom ADCP deployments

Location of ADCP deployment of data

collected

Data analyses on shore due to restrictions in

morning depth of available technology

Factors impacting Factors impacting deployment site deployment site choicechoice

•External factors that can impact the depth, location and available resource:

− Shipping routes− Existing infrastructure that can

utilize the generated energy − Marine Protected Areas

•Technology specific factors:− Operational depth − Turbine Capacity factor− Array configuration and spacing− Instrumentation used for data

capturing

Distance from the assessment sites to closest substation

Parameter Value

Mean [m/s] 1.46Median [m/s] 1.6Mode [m/s] 1.76Standard Deviation [m/s]

0.59

Minimum [m/s] 0Maximum [m/s] 2.82

Agulhas Current: Results from 18 Agulhas Current: Results from 18 month analysismonth analysisCape MorganCape Morgan

Probability of exceedance

Velocity [m/s]

P50 1.6P75 1.15P90 0.44P99 0.1

Natal Pulses

Agulhas Current: Results from 18 Agulhas Current: Results from 18 month analysismonth analysisCape MorganCape Morgan

Turbine specifications

SeaGen Turbine (Siemens, 2012)

Numerical Turbine

Cut in speed 0.8 m/s 0.6 m/sCut out speed 2.5 m/s 2.0 m/sCp 0.45 0.4

Diameter 16 m 16 m

Agulhas Current: Results from 18 Agulhas Current: Results from 18 month analysismonth analysisCape MorganCape Morgan

The capacity factor also gives a good indication of the variability of the site

The achieved capacity factors are considerably lower than expected. This can be accounted for by the lower velocities experienced in ocean currents in comparison to tidal applications which the technology is designed for and

the variability of the Agulhas Current.

Site Capacity factor %

Cape Morgan 50.9East London location 1 50.8East London location 2 47.5

The plot shows the power plot which has averaged over a five day period. This five day averaged power presents a smoother trend plot and highlights where the distinct drop in power occurs

Agulhas Current: Results from 18 Agulhas Current: Results from 18 month analysismonth analysisCape MorganCape Morgan

• Site 1 and site 2 lie 45 km and 25 km respectively from the nearest low voltage station.

• It can be argued that Cape Morgan is the better choice to the East London location 2 for marine turbine deployment due to the improved velocities and lower variability at this chosen site.

• The difference in capacity factor is approximately 3.3% between the two locations, but a techno-economic analysis will have to be carried out in order to see if the greater capacity power produced will compensate for the costs incurred for the longer distance of sea cabling.

Agulhas Agulhas Current: Current: ConclusionConclusion

East London 2

Cape Morgan

1

2

Distance from the assessment sites to closest substation