Transcript Reinecke_J_Meyer_I - Energy Postgraduate Conference 2013

Resource Assessment of the
Agulhas Current to determine
Feasibility for Marine Energy
Extraction
Centre for Renewable and Sustainable Energy Studies
Stellenbosch University
Presenter: Josh Reinecke
Researchers: I. Meyer, J. Reinecke & Prof J. L Van Niekerk
Energy Postgraduate Conference 2013
Ocean Current Energy around
South Africa
Agulhas Current is South
Africa’s strongest ocean
current resource
Viability for energy
extraction?
Agulhas Current: Characteristics
•
Water mass contribution of the Agulhas Current:
–
–
–
Agulhas Current retroflection – largest source
Mozambique Current
The contributions from these two sources
are mostly in the form of eddies or rings
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: Previous Research
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
Mean structure of the Agulhas Current presented by Bryden et al (Bryden, et al., 2005)
•
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
Velocity structure [cm/s] (Beal & Bryden, 1999)
Agulhas Current: Data Analysed
Location of ADCP
deployment of data
collected
Port Edward
Eskom ADCP deployments
#
%
U
%
U
%
U
Waterfall Bluff
#
Port St. Johns
#
Mdumbi estuary
#
Mbashe estuary
#
Kei Mouth
#
Data analyses on shore
due to restrictions in
morning depth of
available technology
Port Elizabeth
%
U
%
U
%
U
%
U
U
T
$
%
U
%
U
%
U
%
U
Port Edward
%
U
East London
200 m
T
$
Nortek
500 m
%
U
Cape Morgan
1000 m
%
U
Fish River
%
U
East London
#
%U
%
%
%
U
U
U
Port Alfred
#
%
U
%
U
Factors impacting
deployment site choice
• 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
Agulhas Current: Results from 18 month analysis
Cape Morgan
Parameter
Value
Mean [m/s]
1.46
Median [m/s]
1.6
Mode [m/s]
1.76
Standard Deviation [m/s]
0.59
Minimum [m/s]
0
Maximum [m/s]
2.82
Probability of
exceedance
P50
P75
P90
P99
Velocity
[m/s]
1.6
1.15
0.44
0.1
Agulhas Current: Results from 18 month analysis
Cape Morgan
Natal Pulses
Agulhas Current: Results from 18 month analysis
Cape Morgan
Turbine
specifications
Cut in speed
Cut out speed
Cp
Diameter
SeaGen Turbine
(Siemens, 2012)
0.8 m/s
2.5 m/s
0.45
16 m
Numerical Turbine
0.6 m/s
2.0 m/s
0.4
16 m
Site
The capacity factor also
Cape Morgan
gives a good indication of
East London location 1
the variability of the site
East London location 2
Capacity factor %
50.9
50.8
47.5
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.
Agulhas Current: Results from 18 month analysis
Cape Morgan
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:
Conclusion
•
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.
Distance from the assessment sites
to closest substation
1
Cape Morgan
2
East London 2