REASSESSMENT OF LILLGRUND OFFSHORE WIND FARM USING

WINDPRO

“A Project”

by

HASEEB AHMAD

Submitted to the Office of Graduate Studies of

Gotland University

in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE IN WIND POWER PROJECT MANAGEMTENT

June, 2012

Major Subject: "Energy Technology"

“Master of science in Wind Power Project Management”

2012

REASSESSMENT OF LILLGRUND OFFSHORE WIND FARM USING

WINDPRO

“A Project”

by

HASEEB AHMAD

Submitted to the Office of Graduate Studies of

Gotland University

in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE IN WIND POWER PROJECT MANAGEMENT

Examiner: Dr. Bahri Uzunoglu

June, 2012

Major Subject: "Energy Technology"

ABSTRACT

The objective of this project is to reassess the Lillgrund Offshore Wind Farm using WindPRO as

a design tool. In this project, current layout of Lillgrund Wind Farm is used along with available

wind resources. The project consists of brief description of the project in terms of location,

components of the wind farm, their specifications and different calculation modules using

WindPRO. The project is reassessed in terms of Environmental Impact (noise, shadow and

visual impact) Annual Energy Production and Electrical Losses. The results obtained from the

calculations are compared with actual results and the difference between calculated and actual

results is discussed.

NOMENCLATURE

GWh Giga Watt hour

Km Kilometer

MW Mega Watt

MWh Mega Watt hour

GPS Global Positioning System

kV Kilo Volt

mm2

Sq. Millimeter

MVA Mega Volt Ampere

kVA Kilo Volt Ampere

WAsP Wind Atlas Analysis and Application Program

NCAR National Center for Atmospheric Research

Contents

LIST OF FIGURES …………………………………………………………………………….…i

LIST OF TABLES ……………………………………………………………………………….ii

Chapter 1 Introduction ................................................................................................................ 1

Project Description ..................................................................................................................... 1

History ........................................................................................................................................ 2

Chapter 2 Wind Farm Components ............................................................................................. 2

Foundations ................................................................................................................................ 2

Turbines ...................................................................................................................................... 4

Substations .................................................................................................................................. 9

Chapter 3 Calculations .............................................................................................................. 10

Noise ..................................................................................................................................... 10

Shadow ................................................................................................................................. 11

Visual Impact ........................................................................................................................ 11

Annual Energy Production ................................................................................................... 13

Electrical Losses ................................................................................................................... 14

Conclusion .................................................................................................................................... 15

VITA ............................................................................................................................................ 16

Bibliography ................................................................................................................................. 17

i

LIST OF FIGURES

Figure 1. Lillgrund Offshore Wind Farm Location ........................................................................ 1

Figure 2. A tug takes the barge with four foundations from Poland to Lillgrund .......................... 3

Figure 3. Eide Barge 5 .................................................................................................................... 6

Figure 4. The Sea Power Vessel ..................................................................................................... 6

Figure 5. Lillgrund Wind Farm Cable Layout ................................................................................ 7

Figure 6. View from Klagshamn harbour 5.3 km ......................................................................... 12

Figure 7. View from Klagshamn harbour 5.3 km using WindPRO ............................................. 12

ii

LIST OF TABLES

Table 1. Specifications of Wind Turbines ...................................................................................... 5

Table 2. Characteristics of vessel used for foundation and turbine installation (Eide Barge 5) ..... 5

Table 3.Characteristics of vessels used for cable installation (CS Pleijel) (Nautilus Maxi) .......... 8

Table 4. Noise Calculations of Lillgrund Wind Farm .................................................................. 10

Table 5. Shadow Calculations of Lillgrund Wind Farm ............................................................... 11

Table 6. Annual energy production results comparing different wake models and wind

distributions .................................................................................................................................. 13

Table 7. Actual production of Lillgrund wind farm ..................................................................... 14

Table 8. Electrical losses of Lillgrund wind farm ........................................................................ 14

1

Chapter 1 Introduction

Project Description

The Lillgrund wind farm is the largest offshore wind farm of Sweden designed to meet the

electricity demand of more than 60,000 homes. The wind farm consists of 48 Siemens 2.3 Mk II

wind turbines. The total wind power plant capacity is 110 MW and an approximate annual

generation is 330 GWh. The wind power plant includes an offshore substation, an onshore

substation and 130 kV sea and land cable for connection to the shore. The Lillgrund offshore

wind farm is located in a shallow area of Öresund, 7 km off the coast of Sweden and 9 km off

the coast of Denmark. The wind power plant is situated 7 km south of the Öresund Bridge,

which connects Copenhagen and Malmö. (Joakim Jeppsson, Poul Erik Larsen, Åke Larrson,

September 2008 )

Figure 1. Lillgrund Offshore Wind Farm Location

2

History

The conditions were quite favorable to establish an offshore wind farm at Lillgrund. The

southern shallow part of Öresund is blessed with good wind speeds which results high energy

production. The closeness to the shore made the access for construction, operation and

maintenance really easy. Water depth is only 4 to 12 meters so cost of foundation was controlled.

(Flodérus, Experiences from the Construction and Installation of Lillgrund Wind Farm, May

2008)The transportation of materials including turbines was easily facilitated and shipped

directly to the site. Weather plays a vital role for developing an offshore wind farm. Proper

monitoring and daily log weather log was kept to make it possible to identify the weather

conditions at any given time.

Chapter 2 Wind Farm Components

Foundations

There are 49 foundations at Lillgrund wind farm. The foundations of 48 turbines and one

offshore substation are made up of gravity reinforced concrete. The Pihl-Hochtief consortium

rented a part of the harbor in Swinoujscie, Poland, to manufacture the foundations. A ready- mix

concrete plant was installed very close to the quay to facilitate concrete production, pouring and

transport. (Flodérus, Experiences from the Construction and Installation of Lillgrund Wind

Farm, May 2008)

The dredging work at seabed was done to achieve the sufficient bearing capacity of seabed. The

excavated area was filled with a 50 cm thick cushion layer of crushed stones, to form a

horizontal base for the foundation. (Flodérus, Experiences from the Construction and Installation

of Lillgrund Wind Farm, May 2008) The diver inspection continued during foundation

3

placement to ensure high quality of work. Four foundations were cast on each individual barge.

As the bolt tolerances were very tight, the bolts were placed in fixing plates before the concrete

was poured into the shutter boarding. The total weight of a foundation is 2000 MT including 500

MT of ballast material on the base plate. (Flodérus, Experiences from the Construction and

Installation of Lillgrund Wind Farm, May 2008) After completion of required work on barge, a

tug pulled the barge from Poland to Lillgrund.

Figure 2. A tug takes the barge with four foundations from Poland to Lillgrund

A crane barge was used to lift the foundations from barge and place them on the specific

location. The exact position of each foundation was mapped precisely with the aid of a four-

anchor system and a global positioning system (GPS) and the crane barge was pulled to each

new location with the aid of a tug and anchors. The whole area of the seabed around the

foundation was covered with a rock-fill scour protection to prevent the ocean currents from

moving seabed material and thus undermining the stability of the foundation.

4

Turbines

The Siemens 2.3 MW Mk II variable speed wind turbines are used. The turbines were

manufactured by Siemens. The rotor and nacelle were made in Jutland, Denmark. The

subcontractors located in Jutland, Denmark made the towers. All the equipment was transported

by lorries to the harbor of Nyborg, Denmark.

The towers (upper and lower sections), the nacelles and the rotors were loaded onto a special

ship by a large crane. The total average time for installing the load of three wind turbines took

five days: One day for the journey from Nyborg to Lillgrund, two days to erect three wind

turbines, one day for the return journey to Nyborg and finally one day to load three more wind

turbines. As long as weather permitted, these activities were carried out 24 hours a day, seven

days a week. (Flodérus, Experiences from the Construction and Installation of Lillgrund Wind

Farm, May 2008)

Rotor type 3-bladed, horizontal axis

Rotor position Upwind

Rotor diameter 93 m

Swept area 6800 m2

Rotor speed 6 to 16 rpm

Aerodynamic regulation Pitch regulation

Yaw system Active

Controller type Microprocessor

SCADA system WPS

Tower Cylindrical

Rotor weight 60 ton

5

Nacelle weight 82 ton

Tower weight (70 m) 134 ton

Table 1. Specifications of Wind Turbines

Wind turbines were installed by the Sea Power with the help of large a crane. The operation took

place 15 meters away from the foundations; the vessel raised itself by two meters by means of

four jack-up legs to stabilize the hull for waves. The elevated deck provided stable platform for

work The Sea Power is capable of operating in marine conditions with wave heights of up to one

meter. Installation of towers and nacelles can be carried out in a wind speed of up to 10 m/s

whilst installation of rotors is limited to a wind speed of maximum 7 m/s. (Flodérus, Experiences

from the Construction and Installation of Lillgrund Wind Farm, May 2008)

Name Eide Barge 5

Owner and Operator Eide Marine Services A/S

Vessel type Heavy Lift Barge

Construction Company Germany

Overall Length 76 m

Breath 37 m

Maximum Draft 3.615 m

Maximum Lifting Capacity 1850 MT

Table 2. Characteristics of vessel used for foundation and turbine installation (Eide Barge 5)

6

Figure 3. Eide Barge 5

Figure 4. The Sea Power Vessel

7

Cables

The Lillgrund offshore wind farm electrical network consists of a series of inter-array cables and

an export cable. Voltage levels are 36 kV for inter-array cables and 145 kV for the export cable.

The inter-array cables connect the wind power generators with the transformer platform

(offshore substation). The inter-array cables are supplied in three different cross sectional sizes

95 mm2, 185 mm

2 and 240 mm

2. (Unosson, January 2009) The thickness of cable increases with

as it goes close to substation. There are 48 inter array cables in total. The length of the cables

varies, with 15 of the cables each approximately 350 meters, 28 of the cables approximately 450

meters and 5 cables up to 1500 meters. (Unosson, January 2009) The export cable connects the

transformer platform with the substation in Bunkeflo. The export cable is divided into a 7 km

submarine cable with a size of 400 mm2 and a 1.7 km land cable with a size of 630 mm

2. The

submarine cables include an integrated optic cable. The onshore cable includes a total of 4

separate cables, three AXLJ 1x 630 mm2 as well as an optic cable. (Unosson, January 2009)

Figure 5. Lillgrund Wind Farm Cable Layout

8

The inter array cable installation was performed with the help of two vessels, C/S Pleijel and

M/S Peter Madsen, and their workboats. C/S Pleijel was responsible for laying down the inter-

array cable between the foundations and M/S Peter Madsen was used as the base for the divers

during the cable pull-in and the post-lay inspection. M/S Peter Madsen also transported ABB

team, tools and material between the foundations. (Unosson, January 2009)

The offshore part of the export cable installation consisted of trenching, laying, pull-in and

burying. The last 300 meters of the export cable, which was to connect to the transformer

platform, was installed on the seabed temporarily until the transformer platform had been

positioned.

The offshore export cable installation was carried out using the barge Nautilus Maxi. First, the

cable was pulled to shore from the barge. Then, all but the last 300 meters of the cable was laid

into the trench. The remaining was to be connected to the transformer platform. (Unosson,

January 2009)

Name C/S Pleijel Nautilus Maxi

Owner and Operator Baltic offshore Seløy under water services AS

Vessel type Cable laying ship Multipurpose/ cable lay barge

Construction Company Denmark Norway

Overall Length 72.4 m 47 m

Breath 13 m 20 m

Accommodation 20 Persons

1st and 2

nd crane capacity 7 tons and 3 tons 400 tons and 150 tons

Carousel and Turntable Capacity 900 tons

Table 3.Characteristics of vessels used for cable installation (CS Pleijel) (Nautilus Maxi)

9

Substations

The offshore substation at Lillgrund is designed to visually harmonize with the marine

environment. The cylindrical substation has a diameter of 22 meters and reaches approximately

25 meters above sea level. The steel framework of the transformer platform was made in Poland.

It was transported to Århus, Denmark, where all electrical equipment was installed, along with

the internal and external walls. The completed transformer station was transported on a barge to

the Copenhagen harbor, where a marine crane lifted it directly to its planned location at

Lillgrund. (Flodérus, Experiences from the Construction and Installation of Lillgrund Wind

Farm, May 2008) The substation consists of the following electrical systems (Joakim Jeppsson,

Poul Erik Larsen, Åke Larrson, September 2008 )

138/33 kV main transformer, 120 MVA, with tap changer

33 kV switchgear for each feeder and the local power supply

33 kV/0.4 kV transformer for local power supply, 150 kVA

0.4 kV switchgear system for local power supply

Emergency diesel for back-up, 110 kVA

Control/monitoring system

Mechanical vibration protective device (which trips all electrical equipment in case of a

ship collision)

Lillgrund offshore wind power plant is connected to E.ON’s 130 kV onshore station Bunkeflo,

near Malmö. The main circuit breaker is located here.

10

Chapter 3 Calculations

WindPRO is employed to make calculations about environment and visual effects, electrical

losses and annual energy production of the Lillgrund wind farm.

Environmental Report

Environmental monitoring measures performed for the Lillgrund offshore wind farm will be

described in the section and the results will be summarized.

Noise

According to environmental court, the equivalent noise level in the areas closest to the beach

shall not exceed 35 db. (Davy, 2009) However, the equivalent noise level measured varied

between 31-46 dB at wind speeds between 2-8 m/s when the initial noise measurement were

performed. The project was still approved by the authorities. (Davy, 2009) Following are the

measurements performed by WindPRO, different noise levels of Siemens 2.3 MW Mk II were

investigated. Eight noise sensitive areas are designated all along the beach.

No.

Noise Sensitive

Areas

Noise

Limit WindPRO Results

Level

0

Level

1

Level

2

Level

3

Level

4

Level

5

1 A 35 44.8 44 42.8 41.8 40.9 40.1

2 B 35 43.6 42.9 41.6 40.6 39.8 39

3 C 35 42.1 41.5 40.2 39.3 38.5 37.7

4 D 35 40 39.5 38.1 37.3 36.6 35.9

5 E 35 39.1 38.6 37.2 36.4 35.7 35

6 F 35 40.7 40.1 38.8 38 37.2 36.5

7 G 35 37.6 37.1 35.7 35 34.3 33.7

8 H 35 41.2 40.6 39.3 38.4 37.7 36.9 Table 4. Noise Calculations of Lillgrund Wind Farm

11

Shadow

Shadow is not generally the point of concern for offshore wind farm developers because these

are situated quite away from the beaches or residential areas. However, shadow calculations are

made by using WindPRO. Nine different shadow receptors are placed along the beach to

measure the effect of wind turbines. Following are the results:

No. Receptors Shadow

hr/year days/year hr/day

1 A 0 0 0

2 B 0 0 0

3 C 0 0 0

4 D 0 0 0

5 E 0 0 0

6 F 0 0 0

7 G 0 0 0

8 H 0 0 0

9 I 0 0 0 Table 5. Shadow Calculations of Lillgrund Wind Farm

Visual Impact

The visualization of the impact of a wind farm on surrounding landscape is an important task

during permitting process. WindPRO is employed to fulfill this task. A view point “Klagshamn

harbour, 5.3 km” is selected and results are calculated using Photomontage module of

WindPRO.

12

Figure 6. View from Klagshamn harbour 5.3 km

Figure 7. View from Klagshamn harbour 5.3 km using WindPRO

13

Annual Energy Production

Wake Model Wind Distribution

Result

Park

MWh/y

Result

-10%

Park

Efficiency

%

Capacity

%

Mean

Wind

Speed

m/s

N.O.Jensen

(Riso/EMD)

Weibull_NCAR_BASIC

_N55.0_E12.5_42 m 229511 206560 69 21.3 6.8

N.O.Jensen

(Riso/EMD)

Measure_NCAR_BASIC

_N55.0_E12.5_42 m 235691.7 212123 70.4 21.9 6.8

N.O.Jensen

(Riso/EMD) WAsP Interface 429089.6 386181 78.1 39.9 9.2

N.O.Jensen

(Riso/EMD) ATLAS 416931.5 375238 78.2 38.3 9.1

Eddy Viscosity

Model

Weibull_NCAR_BASIC

_N55.0_E12.5_42 m 284751.1 256276 85.6 26.5 6.8

Eddy Viscosity

Model

Measure_NCAR_BASIC

_N55.0_E12.5_42 m 288689.7 259821 86.2 26.8 6.8

Eddy Viscosity

Model WAsP Interface 495307.5 445777 90.3 46.1 9.1

Eddy Viscosity

Model ATLAS 482424.6 434182 90.4 44.9 9.1

EWTS

II(G.C.Larsen)

Weibull_NCAR_BASIC

_N55.0_E12.5_42 m 270537 243483 81.3 25.2 6.8

EWTS

II(G.C.Larsen) WAsP Interface 480753.6 432678 87.5 44.7 9.3

Table 6. Annual energy production results comparing different wake models and wind distributions

Initially the measurements taken on a tower located at Lillgrund in Öresund, about 10 km west

of the Swedish coastline, have been analyzed from 1st September 2003 to 28

th February 2006.

The observed mean wind speed was found to be 8.4 m/s at 65 m height. (Bergström, March

2009) The actual production figures from 2008 to 2011 are taken from http://www.vindstat.nu

data base and compared with WindPRO results. Different wind distributions were used in

WindPRO including met mast data (Falsterborev) and NCAR data as shown above. The actual

production results are shown below.

14

Year Av. Production GWh

2008 326.78312

2009 319.97166

2010 303.90538

2011 347.88777

Table 7. Actual production of Lillgrund wind farm

As it can be seen that the results obtained from NCAR data are much closer to the actual

production figures in Table.7. The eddy viscosity wake model gives better solution than other

models. The height of NCAR data is 42 m, and wind speed obtained from NCAR data at 42 m is

6.5 m/s. As described above, the observed wind speed near the site is 8.4 m/s. If we extrapolate

the production, obtained from WindPRO, at 6.8 m/s to 8.4 m/s, the figure come close to the

actual production. So it can be concluded that eddy viscosity model using NCAR data gives

reliable results in this case.

Electrical Losses

Reassessment of electrical losses is done using egrid module of WindPRO.

Table 8. Electrical losses of Lillgrund wind farm

15

These results are calculated using annual energy production of 259821 MWh/year. The losses

are calculated using ambient temperature 20oC. The climate under sea is taken as moderate.

Conclusion

The reassessment of lillgrund wind farm is done using software WindPRO. The results are

obtained using different modules of WindPRO. The results are quite similar to the ones

calculated at the start of the project. While calculating annual energy production, the met mast

located at Falsterborev gave abnormal results possibly due to errors in the data base and also it is

short term data. The NCAR data is more reliable because it is long term. Rest of the modules

calculated accurate results.

16

VITA

Name: Haseeb Ahmad

Address: Gotland University

Cramérgatan 3, 621 67 Visby, Sweden

Email Address: haseeba@mail.hgo.se

Education: Bachelor’s in Chemical Engineering. The University of Engineering and

Technology Lahore, Pakistan, 2003

Certified Professional Manager in Health, Safety and Environment, Pakistan

Institute of Modern Studies, 2011

Masters in Wind Power Project Management, Gotland University Sweden,

2012

17

Bibliography

Bergström, H. (March 2009). Meteorological Conditions at Lillgrund. Sweden: The Swedish

Energy Agency.

CS Pleijel. (n.d.). Retrieved March 14, 2012, from

http://www.4coffshore.com/windfarms/vessel-cs-pleijel-vid5.html

Davy, T. (2009). Environmental Monitoring- Lillgrund Offshore Wind Farm. Sweden: The

Swedish Energy Agency.

Eide Barge 5. (n.d.). Retrieved March 13, 2012, from 4coffhore:

http://www.4coffshore.com/windfarms/vessel-eide-barge-5-vid55.html

Flodérus, A. (May 2008). Experiences from the Construction and Installation of Lillgrund Wind

Farm. Sweden: The Swedish Energy Agency.

Flodérus, A. (May 2008). Experiences from the Construction and Installation of Lillgrund Wind

Farm. Sweden: The Swedish Energy Agency.

Joakim Jeppsson, Poul Erik Larsen, Åke Larrson. (September 2008 ). Technical Description

Lillgrund Wind Power Plant. Sweden: The Swedish Energy Agency .

Nautilus Maxi. (n.d.). Retrieved March 14, 2012, from

http://www.4coffshore.com/windfarms/vessel-nautilus-maxi-vid28.html

Unosson, O. (January 2009). Offshore Cable Installation - Lillgrund. Sweden: The Swedish Energy

Agency.