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Offshore wind energy resources
Gaetano Gaudiosi
21 MARCH 2007
After the introductory session of the Offshore Wind Energy
on the 1st March 2007
today
How to choose the offshore wind farm areas and evaluate the
offshore potential
Offshore wind farm Siting and energy potential
Offshore Wind Resources
Technical , economic, environmental limit
Constraints of the sea space utilizations
Waves
Currents
Bathimetry
Sea bed morphology and geology
Offshore wind potential
Offshore wind farm approuved areas
An application
A typical offshore wind farm
Offshore turbines are mounted on a tower, in turn
mounted on a platform
connected to the foundations.
•
The foundations may be a monopile sunk into the
seabed, an anchored tripod, or a caisson (basket)
filled with aggregate. Foundations may be
surrounded by rocks for protection from scouring
action of currents.
A network of cables connects individual turbines to
a separate platform with electrical switchgear and
transformers which condition the power ready for
transmission, along a cable to an onshore substation.
From the sub-station the power is conveyed directly
into the onshore network. Other marine renewables
may share similar electrical infrastructure as shown
Offshore Wind Farm
Piles (1) are driven into the seabed . Erosion protection, similar to sea defences, are placed at the base to
prevent damage to the sea floor. The top of the foundation is painted a bright colour to make it visible to
ships and has an access platform to allow maintenance teams to dock.
Once the turbine is assembled, sensors on the turbine detect the wind direction and turn the head, known as
the nacelle , to face into the wind, so that the blades can collect the maximum amount of energy. The
movement of the wind over the aerodynamically shaped blades (2) makes them rotate around a horizontal
hub, which is connected to a shaft inside the nacelle (3). This shaft, via a gearbox, powers a generator to
convert the energy into electricity. Subsea cables (4) take the power to an offshore transformer (5) which
converts the electricity to a high voltage (33kV) before running it back 5 -10 miles to connect to the grid at
a substation on land (6)
Foundation of turbines in various water depths
Floating turbine Platform and ocean environmental
parameters
Technical , economic, environmental limit
- Larger water depth is a technical and economic limit to
wind farm installation due to the foundation increasing cost .
-Small distance from the coast is a landscape limit for visual
impact of the offshore wind farm, large distance is an
economic limit for the cable connection to the onshore
electric grid.
The current global satellite network
.
Cup anemometer with vane
Weather stations aboard buoys in the Atlantic Ocean,
Offshore wind measurements
Wind measurements –Meteo Mast Offshore MeteorologyThe instrumentation
of the meteorological
mast consists of cup and
ultrasonic anemometers
and wind vanes in all
heights ranging from
33 m up to 100 m
above sea level.
The arrangement of the
instruments can be seen
on the photo.
Offshore Wind Resources-Surface pressure forecast
Offshore wind characteristics
European Offshore Wind Map
The Offshore Wind Resources and Constraints
• The size of the offshore wind resource is impressive. A
study carefully examined all the relevant offshore
constraints excluded all the following areas from the
resource assessment:
• everything closer to the shore than 5 km
• shipping lanes
• military exercise areas
• regions where dredging concessions existed
• known dumping grounds for ammunition, explosives and
other hazardous materials
• areas with sea depth less than 10m or greater than 50m
The Offshore Resource-a
The last three constraints would be considered less valid in
future years. The distance to the shoreline may depend upon
the planning classification of the land in question and
existing sea uses. Regions with dredging concessions may be
considered, depending upon the depth of water and draught
of vessels used. Technological development relating to the
foundations upon which turbines stand mean that water
depth can now be well under 10 metres. Part of the area of
the proposed Scroby Sands wind farm is a sand bank at low
tide.
US offshore Wind Resources
Oceanographic measurements
Oceanographic measurements cover
the monitoring of waves, currents, sea
level, salinity and oxygen content.
Record time series of parameters
are measured to document a large
number of offshore conditions.
Meteorological and oceanographic
measurements provide important data
for designing offshore foundations
and wind turbine constructions as
well as for project profitability
calculations. Besides, they enable
the improvement of atmosphericphysical and oceanographic models
and serve the marine environmental
monitoring.
Wave
Wave map as set out by Dr Tom Thorpe (ETSU
1998 ,Wave Energy Commentary).
The highest energy waves are concentrated off the
western coasts in the 40o–60o latitude range north
and south. The power in the wave fronts varies in
these areas between 30 and 70 kW/m with peaks to
100kW/m in the Atlantic SW of Ireland, the
Southern Ocean and off Cape Horn.
Global Distribution of Deep Water Wave Power Resources
Ocean Circulation –Currents-a
The circulation of the world's oceans is important in the latitudinal
redistribution of energy. Warm ocean currents are corridors of warm water
moving from the tropics poleward where they release energy to the air.
Cold ocean currents are corridors of cold water moving from higher latitudes
toward the equator. They absorb energy received in the of ocean currents and
the air circulation above them can be made.
The major ocean currents are wind-driven currents, though some ocean
currents result from density and salinity tropics thus cooling the air above. A
distinct correlation between the pattern variations of water. The subtropical
high pressure cells are responsible for many of the Earth's great ocean
currents.
Ocean Circulation –Currents-b
Examine the location of the subtropical highs and then place their
position on the map of world ocean currents. Notice how the position of
the subtropical highs and the circulation around them coincide with the
circulation of many of the world's ocean currents.
Take the Gulf Stream for example. As air blows out of the western side of
the subtropical high it flows over a warm pool of subtropical water
dragging it northward creating a warm ocean current. Approaching the
eastern seaboard of the United States it is deflected toward the northeast
flowing towards the north Atlantic and Europe. After crossing the Atlantic
it turns into the North Atlantic Current (Drift). The Gulf Stream enhances
instability and the likelihood for precipitation as air passes over it. The
warmth of the North Atlantic Drift moderates the climate of British Isles.
Major ocean currents
The legal continental shelf
Under the law of the sea a
nation can extend its territorial
claim of the ocean floor if the
surrounding continental area
extends more than 200 nautical
miles offshore. The maximum
limit of this additional area is
350 nautical miles offshore. In
2005 New Zealand was
preparing a submission to
extend its legal jurisdiction to
the maximum limit
Sea bed morphology and geology
Sea bed morphology and structural configuration
are very important for the type of foundation tobe
used for the support platform of the wind turbine.
Water depth is a structural and economic limiting
factor for foundation . Increasing the water depth
the size of the wind turbine should increase .
A geological evaluation should be carried out in
the design phase of the wind farm to choose the
correct type of foundation
Bathimetry
Bathimetry and a wind farm
Nordsee: Offshore-Windparks
Baltic Offshore-Windparks
OFFSHORE WIND POTENTIAL
After the identification of all areas of wind farm application
according water depth , distance from the coast and other
constraints their total gives the usable sea surface.
Assuming a surface wind farm power density ( MW/ Kmq) it
is possible to evaluate the potential in GW.
The surface power density results from the size and mutual
distance of turbines according their wind interference.
Assuming a mean value of equivalent hours/ year of
Electricity generation for the standard turbine nominal power
it is possible to evaluate the TWh/year of regions or countries.
Horns Rev Wind Farm-Denmark
Application (Example)
An Assessment of Offshore
Wind Energy Potential
Using Mesoscale Model and
GIS
Atsushi YAMAGUCHI
Takeshi ISHIHARA
Yozo FUJINO
University of Tokyo, Japan
Economical criteria
Social criteria
Mesoscale Model-a
Annual mean wind speed
Available Potential
Available potential for each water depth class-a
Available potential for each water depth class-b
Available potential for each water depth class-c
Most of the available potential is located at the east offshore
of Chiba and Ibaraki especially at the offing of Choshi while
available area is limited around Sagami Bay because of the
sea bed topography.
Considering all the economical and social criteria, the total
available energy potential in this area is 94TWh/year,
accounting for 32% of the annual demand of TEPCO.
Weather forecasting
Accurate forecasts have the potential
for the following benefits:
-Improved market trading
- Optimised scheduled maintenance
- Enhanced plant scheduling by
system operators
Forecast programs have predicted the
long term energy production of wind
farms on a commercial basis for more
than 20 years, and have analysed more
than 50,000 MW of projects.
Techniques on short term forecasting
have been built on the experience
gained from this work.