Offshore wind energy resourcesGaetano 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 ResourcesTechnical , economic, environmental limitConstraints of the sea space utilizationsWavesCurrentsBathimetrySea bed morphology and geologyOffshore wind potentialOffshore wind farm approuved areasAn 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

S c o p eC o d e C o m p a r i s o n s f o r :

• W a v e l o a d i n g

• S u p p o r t s t r u c t u r e s

• G e o t e c h n i c a l

• C o u p l e d s y s t e m d y n a m i c s

G o a l1 . Q u a n t i f y o f f s h o r e

l o a d p r e d i c t i o n c a p a b i l i t y

2 . I d e n t i f y c r i t i c a l m o d e l i n g d e f i c i e n c i e s c o m m o n t o a l l c o d e s .

L e a d : S a n d y B u t t e r f i e l d - U S D O E / N R E L

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

Offshore wind measurements

Weather stations aboard buoys in the Atlantic Ocean,

Wind measurements –Meteo Mast Offshore Meteorology-

The 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

W h a t i s t h e W i n d S p e e d = ? ?

N e u t r a l B o u n d a r y L a y e r

C o n v e c t i v e B o u n d a r y L a y e r

S t a b l e B o u n d a r y L a t e r w i t h L o w L e v e l

J e t

G r a p h i c C r e d i t : B r u c e B a i l e y A W S T r u e w i n d

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

atmospheric-physical 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 thewestern coasts in the 40o–60o latitude range northand south. The power in the wave fronts varies inthese areas between 30 and 70 kW/m with peaks to100kW/m in the Atlantic SW of Ireland, theSouthern 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 ofthe subtropical highs and the circulation around them coincide with thecirculation of many of the world's ocean currents. Take the Gulf Stream for example. As air blows out of the western side ofthe 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 applicationaccording water depth , distance from the coast and otherconstraints 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 mutualdistance 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 PotentialUsing Mesoscale Model and GIS

Atsushi YAMAGUCHITakeshi ISHIHARA Yozo FUJINOUniversity 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 forecastingAccurate forecasts have the potentialfor the following benefits: -Improved market trading

- Optimised scheduled maintenance- Enhanced plant scheduling by

system operators

Forecast programs have predicted thelong term energy production of windfarms on a commercial basis for morethan 20 years, and have analysed morethan 50,000 MW of projects.Techniques on short term forecastinghave been built on the experiencegained from this work.