AckermannTh. (ed) Wind Power in Power Systems

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Introduction

Thomas Ackermann

Wind energy is gaining increasing importance throughout the world. This fast develop-

ment of wind energy technology and of the market has large implications for a number

of people and institutions: for instance, for scientists who research and teach future wind

power, and electrical engineers at universities; for professionals at electric utilit ies who

really need to understand the complexity of the positive and negative effects that wind

energy can have on the power system; for wind turbine manufacturers; and for devel-

opers of wind energy projects, who also need that understanding in order to be able to

develop feasible, modern and cost-effective wind energy projects.

Currently, five countries – Germany, USA, Denmark, India and Spain – concentrate

more than 83 % of worldwide wind energy capacity in their countries. Here, we also find

most of the expertise related to wind energy generation and its integration into the

power system in those countries. However, the utilisation of this renew able source of

power is fast spreading to other areas of the world. This requires the theoretical know-

ledge and practical experience accumulated in the current core markets of wind energy

to be transferred to actors in new markets. A main goal of this book is to make this

knowledge available to anybody interested and/or professionally involved in this area.

The utilisation of wind energy has a tradition of about 3000 years, and the technology

has become very complex. It involves technical disciplines such as aerodynamics,

structural dynamics and mechanical as well as electrical engineering. Over past years a

number of books on aerodynamics and the mechanical design of wind power have been

published. There is, however, no general publication that discusses the integration of

wind power into power systems. This books aims to fill this gap.

I first realised the need for such a book in 1998, shortly after arriving at the Royal

Institute of Technology in Stockholm. There I met Lawrenc e Jones who wrote his PhD

Wind Power in Power Systems Edited by T. Ackermann

Ó 2005 John Wiley & Sons, Ltd ISBN: 0-470-85508-8 (HB)

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on high-voltage direct-current (HVDC) technology. We had long discussions on pos-

sible applications of HVDC technology for offshore wind farms. The more we discussed,

the more questions there were. As a result, in 2000 we organised a workshop on the topic

of ‘HVDC Transmission Networks for Offshore Wind Farms’. This workshop turned

out to be a successful forum for the discussion of this subject, resulting in the decision to

hold workshops on the same subject in 2001 and 2002. The discussions during these

workshops became broader and so did the subject of the workshop. Hence, in 2003 the

workshop was entitled the ‘Fourth International Workshop on the Large-Scale Integra-

tion of Wind Power and Transmission Networks for Offshore Wind Farms’. That time,

the co-organiser was Eltra, the transmission system operator of Western Denmark, and

175 participants from academia and industry attended the workshop.

(1)

During the workshops it became clear that the subject of wind power in power

systems met an increased general interest. In order to satisfy this interest, the initial

idea was simply to summarise the papers from the workshop. This turned out to be more

complicated than initially assumed. Designing a publication that can be of interest to a

wider readership, including professionals in the industry, authorities and students, was

not easy. Another ch allenge was to keep the content to a large extent consistent. Finally,

I wanted to include not only papers from the workshop but also contributions from

other authors who are renowned researchers in this field.

The final version of the book now comprises four parts. Part A aims to present basic

theoretical background knowledge. Chapter 2 gives a brief overview of the historical

development and current status of wind power, and Chapter 3 provides a brief introduc-

tion to wind power in power systems. Here, Chapter 4, which was written by Anca-Daniela

Hansen, is central to the entire book as it presents an overview of current wind turbine

designs. Throughout the book, the authors refer to wind turbine designs (types A, B, C and

D) from Chapter 4 and do not describe them in the individual chapters again. In addition,

this part of the book presents power quality standards (Chapter 5), power quality mea-

surements (Chapter 6), network interconnection standards (Chapter 7) as well as a general

discussion of power system requirements regarding wind power (Chapter 8) and of the

value that wind power contributes to a power system (Chapter 9).

Part B showcases practical international experience regarding the integ ration of wind

power. It starts with contributions from Eltra, the transmission system operator (TSO)

in Western Denmark (Chapter 10) and the German TSO E.on Netz (Chapter 11). These

(1)

Thanks to the members of the International Advisory Committee of the first four workshops: Go

ran

Andersson (Swiss Federal Institute of Technology, Zurich, Switzerland), Gunnar Asplund (ABB, Sweden),

Peter Christensen (NVE, Denmark), Paul Gardner (Garrad Hassan , Siegfried Heier (University of Kassel,

ISET, Germany), Hans Knudsen (Danish Energy Agency), Lawrence Jones (University of Washington,

Seattle, USA), James Manwell (University of Massachusetts, Amherst, USA), Patrice Noury (Alstom, France)

and Lennart So

der (Royal Institute of Technology, Stockholm, Sweden).

Thanks also to the following persons, who helped with or supported the organisation of the workshop in

various ways over the years: Peter Bennich, Lillemor Hyllengren, Lawrence Jones, Valery Knyazkin, Magnus

Lommerdal, Jonas Persson, Julija Matevosyan, Lennart So

der, Erik Thunberg (at the time all members of the

Department of Electrical Engineering, Royal Institute of Technology, Stockholm, Sweden), Jari Ihonen

(Royal Institute of Technology, Stockholm, Sweden), Lawrence Jones (University of Washington, Seattle,

USA), Jens Hobohm (Prognos AG, Germany), Ralf Leutz (at that time with the Tokyo University of

Agriculture and Technology) and Peter Børre Eriksen, Gitte Agersæk and John Eli Nielsen (all at Eltra,

Denmark).

2 Introduction

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are the TSOs that probably have to deal with the largest wind power penetration

worldwide. The discussion of the situation in California (Chapter 12) and on the Swedish

island of Gotland (Chapter 13) focuses on the integration of comparatively simple wind

turbines. Practical experience from wind power in isolated systems is presented in

Chapter 14 and from developing countries such as India in Chapter 15. A more general

discussion on practical experience regarding power quality and wind power is presented

in Chapter 16. Part B also includes chapters on current issues regarding wind power

forecasting (Chapter 17). Finally, we present economic issues that have arisen in the

integration of wind power in the deregulated electricity industry (Chapter 18).

Part C discusses future concepts related to an increasing penetration level of wind

power in power systems. The issues cover voltage control (Chapter 19), transmission

congestion (Chapter 20) and the active management of distribution systems (Chapter

21). Additionally, this part discusses transmission solutions for offshore wind farms

(Chapter 22) and the use of hydrogen as an alternative means of transporting wind

power (Chapter 23).

Finally, Part D shows how dynamic modelling is used to study the impact of the large-

scale integration of wind power. As a start, general wind power modelling issues are

presented and discussed (Chapter 24). This is followed by chapters on low-order models

(Chapter 25) and high-order models (Chapter 26) for wind turbines as well as on the full

verification of dynamic wind turbine models (Chapter 27). The impact of wind power on

power system dynamics is presented in Chapter 28, and the last chapter of the book

(Chapter 29) discusses aggregated wind turbine models that represent a whole wind

farm rather than a single wind turbine.

Owing to the large number of contributors it has not always been pos sible to avoid

overlaps between chapters. Even though I have tried to limit them, the existing overlaps

show that there may be diverging opinions regarding individual subjects. The careful

reader will certainly notice these overlaps and sometimes even contradictions. There

remains a substantial amount of research to be done and experience to be gathered in

order to arrive at a more consistent picture.

Initially, it was my intention to win contributors not only from academia and TSOs

but also from wind turbine manufacturers, as these have valuable experience to share.

However, with the exception of one wind turbine manufacturer, the design of this book

was considered to be too ‘academic’ by those I approached. In my opinion, wind turbine

manufacturers have been developing and introducing interesting solutions for the

integration of wind power into power systems and should present such solutions in

any possible future edition of this book.

I would like to thank all authors of the individual chapters for supporting this time-

consuming project. I would also like to thank Kathryn Sharples, Simone Taylor, Emily

Bone, Lucy Bryan, Rachael Catt and Claire Twine from Wiley for their continuous

support and great patience, and Do

rte M u

ller from Powerwording.com for her language

editing, which has improved the book’s general readability. I would also like to thank

Professor Lennart So

der and the entire Department of Electrical Engineering at the

Royal Institute of Technology, Stockholm, Sweden. Special thanks go also to Go

ran

Andersson, now with the Swiss Federal Institute of Technology, Zurich, Switzerland, who

was very open to the initial idea of holding workshops on these subjects. He also provided

valuable comments on the workshops and this book.

Wind Power in Power Systems 3

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I hope that the book proves to be a useful source of information and basis for

discussion for readers with diverse backgrounds.

In connection with this publication, the editor wi ll introduce a website (http://

www.windpowerinpowersystems.info) with more information regarding this book, a

discussion group and information on forthcoming workshops an d other events.

4 Introduction

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Part A

Theoretical

Background and

Technical

Regulations

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Historical Development and

Current Status of Wind Power

Thomas Ackermann

2.1 Introduction

The power of the wind has been utilised for at least 3000 years. Until the early twentieth

century wind power was used to provide mechanical power to pump water or to grind

grain. At the beginning of modern industrialisation, the use of the fluctuating wind

energy resource was substituted by fossil fuel fired engines or the electrical grid, which

provided a more consistent power source.

In the early 1970s, with the first oil price shock, interest in the power of the wi nd

re-emerged. This time, however, the main focus was on wind power providing electrical

energy instead of mechanical energy. This way, it became possible to provide a reliable

and consistent power source by using other energy technologies – via the electrical grid –

as a backup.

The first wind turbines for electricity generation had alrea dy been developed at the

beginning of the twentieth century. The technology was improved step by step from the

early 1970s. By the end of the 1990s, wind energy has re-emerged as one of the most

important sustainable energy resources. During the last decade of the twentieth century,

worldwide wind capacity doubled approximately every three years. The cost of elec-

tricity from wind power has fallen to about one sixth of the cost in the early 1980s.

And the trend seems to continue. Some experts predict that the cumulative capacity

will be growing worldwide by about 25 % per year until 2005 and costs will be

dropping by an ad ditional 20 to 40 % during the same time period (Wind Power

Monthly 1999).

Wind Power in Power Systems Edited by T. Ackermann

Ó 2005 John Wiley & Sons, Ltd ISBN: 0-470-85508-8 (HB)

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Wind energy technology itself also moved very fast in new dimensions. At the end of

1989 a 300 kW wind turbine with a 30-meter rotor diameter was state of the art. Only 10

years later, 2000 kW turbines with a rotor diameter of around 80 meters were available

from many manufacturers. The first demonstration projects using 3 MW wind turbines

with a rotor diameter of 90 meter were installed before the turn of the century. Now, 3 to

3.6 MW turbines are commercially available. By the time of writing (early 2004),

4–5 MW wind turbines a re under development or have already been tested in demon-

stration project s (see also Table 2.1), and 6–7 MW turbines are expected to be built in

the near future.

In Section 2.2 a more detailed historical overview of wind power development is

provided; in Section 2.3 the current status is presented and in Section 2.4 a brief introduc-

tion to different wind turbine designs is given. The current status regarding network

integration (e.g. penetration levels in different countries) will be presented in Chapter 3.

2.2 Historical Background

The following historical overview divides the utilisation of the natural resource

wind into the generation of mechanical power and the production of electricity

(The historical development of wind turbine technology is documented in many pub-

lications, for instance see Ancona, 1989; Gipe, 1995; Heymann, 1995; Hill, 1994;

Johnson, 1985; Kealey, 1987; Koeppl, 1982; Putnam, 1948; Righter, 1996; Shepherd,

1990, 1994).

2.2.1 Mechanical power generation

The earliest windmills recorded were vertical axis mills. These windmills can be

described as simple drag devices. They have been used in the Afghan highlands to grind

grain since the seventh century

BC.

The first details about horizontal axis windmills are found in historical documents

from Persia, Tibet and China at about 1000

AD. This windmill type has a horizontal

Table 2.1 Development of wind turbine size between 1985 and

2004 (Reproduced by permission of John Wiley & Sons, Ltd.)

Year Capacity (kW) Rotor diameter (m)

1985 50 15

1989 300 30

1992 500 37

1994 600 46

1998 1500 70

2003 3000–3600 90–104

2004 4500–5000 112–128

8 Historical Development and Current Status

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shaft and blades (or sails) revolving in the vertical plane. From Persia and the Middle

East, the horizontal axis windmill spread across the Mediterranean countries and

Central Europe. The first horizontal axis windmill appeared in England around 1150,

in France in 1180, in Flande rs in 1190, in Germany in 1222 and in Denmark in 1259.

This fast development was most likely influenced by the Crusaders, taking the know-

ledge about windmil ls from Persia to many places in Europe.

In Europe, windmill performance was constantly improved between the twelfth and

nineteenth centuries. By the end of the nineteenth century, the typical European wind-

mill used a rotor of 25 mete rs in diameter, an d the stocks reached up to 30 meters.

Windmills were used not only for grinding grain but also for pumping water to drain

lakes and marshes. By 1800 about 20 000 modern European windmills were in operation

in France alone, and in the Netherlands 90 % of the power used in the industry was

based on wind energy. Industrialisation then led to a gradual decline in windmills, but in

1904 wind energy still provided 11 % of the Dutch industrial energy and Germany had

more than 18 000 installed units.

When the European windmills slow ly started to disappear, windmills were introduced

by settlers in Nort h Ame rica. Small windmills for pumping water to livestock became

very popular. These windmills, also known as American W indmills, operated fully self-

regulated, which means they could be left unattended. The self-regulating mechanism

pointed the rotor windward during high-speed winds. The European style windmills

usually had to be turned out of the wind or the sailing blades had to be rolled up during

extreme wind speeds, to avoid damage to the windmill. The popularity of windmills in

the USA reached its peak between 1920 and 1930, with about 600 000 units installed.

Various types of American Windmills are still used for agricultural purposes all over the

world.

2.2.2 Electrical power generation

In 1891, the Dane Poul LaCour was the first to build a wind turbine that generated

electricity. Danish engineers improved the technology during World Wars 1 and 2 and

used the technology to overcome energy shortages. The wind turbines by the Danish

company F. L. Smidth built in 1941–42 can be considered forer unners of modern wind

turbine generators. The Smidth turbines were the first to use modern airfoils, based on

the advancing knowledge of aerodynamics at this time. At the same time, the American

Palmer Putnam built a giant wind turbine for the American company Morgan Smith

Co., with a diameter of 53 meters. Not only was the size of this machine significantly

different but also the design philosophy differed. The Danish philosophy was based on

an upwind rotor with stall regulation, operating at slow speed. Putnam’s design was

based on a downwind rotor with variable pitch regulation. Putnam’s turbine, however,

was not very successful. It was dismantled in 1945. See Table 2.2 for an overview of

important historical wind turbines.

After World War 2, Johannes Juul in Denmark developed the Danish design phil-

osophy further. His turbine, installed in Gedser, Denmark, generated about 2.2 million

kWh between 1956 and 1967. At the same time, the German Hu

tter developed a new

approach. His wind turbine comprised two slender fibreglass blades mounted downwind

of the tower on a teetering hub. Hu

tter’s turbine became known for its high efficiency.

Wind Power in Power Systems 9

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Despite the early success of Juul’s and Hu

tter’s wind turbines, the interest in large-

scale wind power generation decli ned after World War 2. Only small-scale wind turbines

for remote-area power systems or for battery charging received some interest. With the

oil crises at the beginning of the 1970s, the interest in wind power generation returned.

As a result, financial support for research and development of wind energy became

available. Countries such as Germany, the USA and Sweden used this money to develop

large-scale wind turbine prototypes in the megawatt range. Many of these prototypes,

however, did not perform very successfully most of the time (see Table 2.3) because of

various technical problems (e.g. with the pitch mechanisms).

Table 2.2 Historical wind turbines

Turbine and country Diameter

(m)

Swept

Area

)

Power

(kW)

Specific

Power

(kW/m

)

Number

of blades

Tower

height

(m)

Date in

service

Poul LaCour, Denmark 23 408 18 0.04 4 — 1891

Smith-Putnam, USA 53 2231 1250 0.56 2 34 1941

F. L. Smidth, Denmark 17 237 50 0.21 3 24 1941

F. L. Smidth, Denmark 24 456 70 0.15 3 24 1942

Gedser, Denmark 24 452 200 0.44 3 25 1957

tter, Germany 34 908 100 0.11 2 22 1958

Source: Gipe, 1995, page 18 (Reproduced by permission of John Wiley & Sons, Ltd.).

Table 2.3 Performance of the first large-scale demonstration wind turbines

Turbine and country Diameter

(m)

Swept area

)

Capacity

(MW)

Operating

hours

Generated

GWh

Period

Mod-1, USA 60 2827 2 — — 1979–83

Growian, Germany 100 7854 3 420 — 1981–87

Smith-Putnam, USA 53 2236 1.25 695 0.2 1941–45

WTS-4, USA 78 4778 4 7 200 16 1982–94

Nibe A, Denmark 40 1257 0.63 8 414 2 1979–93

WEG LS-1, GB 60 2827 3 8 441 6 1987–92

Mod-2, USA 91 6504 2.5 8 658 15 1982–88

sudden I, Sweden 75 4418 2 11 400 13 1983–88

Mod-OA, USA 38 1141 0.2 13 045 1 1977–82

Tjæreborg, Denmark 61 2922 2 14 175 10 1988–93

cole, Canada 64 4000 3.6 19 000 12 1987–93

Mod-5B, USA 98 7466 3.2 20 561 27 1987–92

Maglarp WTS-3, Sweden 78 4778 3 26 159 34 1982–92

Nibe B, Denmark 40 1257 0.63 29 400 8 1980–93

Tvind, Denmark 54 2290 2 50 000 14 1978–93

Source: Gipe, 1995, page 104.

10 Historical Development and Current Status