Swedish Wind Pioneers Make a Come-back

by S Engström, Ägir konsult AB, Sweden

Introduction

It is twenty years since the modern development of wind power started in the aftermath of the oil crisis in the mid 1970s. Sweden was one of the early pioneers in this development and there is a large effort currently under way to develop large size, two-bladed, flexible designs with improved economic potential.

Pioneer in MW Wind Turbines

Sweden was one of the early pioneers in modern wind power development. The first 60 kW test unit was erected in 1977 and the decision to build MW-sized units was taken the following year. The Maglarp 3 MW unit was the most successful one built. Between its start-up in 1982 and its demolition in 1993 - ironically in excellent working condition and making a profit - it produced a total of 38 GWh, more than any other wind turbine in the world so far. It also produced a lot of data and experience regarding the two-bladed, light-weight, flexible design concept.
 An environmental bonus of currently SEK0.10/kWh (where SEK is the Swedish krona) further increased interest and made the market expand by as much as 90% in 1995. In may 1996, a total of almost 70 MW and 220 wind turbines had been realised, putting Sweden sixth in the European wind league.

Green Power for the Railway

"Green power" - power produced by wind, hydro (in old plants) and biomass - is now being introduced by environmentalists. In a few years it may not be possible to sell electricity generated by other means. This environmental lobby has encouraged the utility Sydkraft to sign a contract with the Swedish Railways to provide wind power. This is promising, as Sydkraft today has no wind power, except for a small off-shore pilot plant, and it is only a few years since the company axed the Maglarp turbine.

Siting Problems

Environmental arguments are also used by groups that oppose the introduction of wind power because of visual impact and noise. They also they claim the electricity production is negligible. In some areas all building permit applications are opposed and the authorities do not give much support. On Gotland, home of most wind turbines in Sweden, the provincial council recently found that the interest of a neighbour to have his view unobscured was just as important as the interest of the Vattenfall utility to erect some wind turbines, and thus cancelled the building permit. This may be logical, since parliament has not yet set a goal for wind power development.
 A particular problem in Sweden is that the military claim that wind power will blind their radar and passive radio signal intelligence activities. In a 1988 investigation of wind power siting, they succeeded in withdrawing areas corresponding to more than 10,000 MW. Today, this is the single major obstacle to siting.
 Off-shore wind power may be the major solution to the siting problems. Fishermen, a small but highly vocal group, have demonstrated some opposition, but the impact on the fish population (and thus in the long run on fishing) may be positive rather than negative. Other environmental constraints can be handled, and out at sea there is plenty of wind.
 Off-shore wind power, however, demands quite large units, since the cost for foundation and grid connection is high and little dependent on the size of the turbine. These larger wind turbines have begun to appear on the market. This may be where the emerging Swedish wind turbine industry will find its main role in the future.

Two-blade Design

Since the beginning of modern wind power development it has been well known that a two-bladed wind turbine has a potential cost benefit of 10-20% compared with a three-bladed design - since it produces about the same output (for the same blade diameter), but requires less material. But it is much harder to design, since the two-bladed turbine is less symmetrical, compared with the three-blader.
 In Sweden today there are three manufacturers developing wind turbines. All the turbines are two-bladed, flexible designs, resulting from the Swedish tradition of research in this area and the knowledge that, when entering the market today, it is necessary to have a solution which offers the best economical potential.
 Kvaerner Turbine AB started designing the first Näsudden 2 MW unit in 1978 (under the name of KMW). In 1993, in co-operation with MBB, the company erected a 3 MW unit in Germany and furnished the existing Näsudden concrete tower with the latest machinery including new blades. Both the Swedish and German units are being evaluated as part of the CEC-sponsored WEGA II programme.
 The operational record of the new Näsudden unit has been excellent after two years it has produced more than the old turbine did in its six years. But it is still too expensive to compete commercially. An extensive study has looked at the possibilities for reducing the costs to the level of today's commercial but smaller wind turbines. The results are encouraging and the problem now is to find the financing for a new project.

Learning from Maglarp

A new development line, initiated some years ago by Nordic Windpower AB, aimed to fully exploit the Swedish tradition of flexible, two-bladed designs. The result became the Nordic 500 and 1000 kW units. The development of both turbines has been supported by Vattenfall AB and NUTEK. The Nordic 1000 is also sponsored by the CEC Joule II programme. The 400 kW prototype of the Nordic 500 wind turbine was erected at Lysekil in 1992. It weighs about 40% less than comparable commercial wind turbines. Before marketing on a larger scale, an initial series of ten units is planned.
 The prototype Nordic 1000 was erected in April 1995 at Näsudden, close to the Kvaerner 3 MW unit. After commissioning, a two-year evaluation will be performed to the standard of the other Joule II and WEGA II projects. Compared to the Nordic 500, the Nordic 1000 turbine is a little less flexible, which means that the fatigue strength is better utilised. The addition of some new load cases in the provisional IEC standard also pushed the design in this direction.
 Both turbines exhibit an extremely low specific weight, ie the weight of the machinery and turbine divided by the turbine swept area (see Table). The low weight and a simple, highly integrated design give both turbines a good commercial potential.

Passive Pitch Design

Zephyr Energy AB is a company in Falkenberg on the West coast of Sweden. During 1989-92 it produced three units of its 250 kW wind turbine model that is based on a proprietary passive pitch regulation developed by the inventor Sven Svenning. The turbines are quite unique in that they possess blades with individual flapping hinges. A series of 3 units will be built in 1996. Zephyr is also working on a 750 kW version with variable speed.

Table: Parameters of Swedish wind turbines

 

Zephyr 250

Nordic 500

Zephyr 750

Nordic 1000

Kvaerner 3 MW

Type of design

Flexible

Flexible

Flexible

Flexible

Rigid

Control principle

Passive pitch

Stall

Passive pitch

Stall

Passive pitch

Hub

Flapping

Teeter

Flapping

Teeter

Flapping

Orientation

Upwind

Upwind

Upwind

Upwind

Upwind

Turbine diameter (m)

28

36

49

53

80

Rotational speed (rpm)

36/54

27/41

var. 13-35

17/25

14/21

Tip speed (m/s)

53/79

51/76

33-90

46/69

59/88

Tower type

Steel shell

Steel shell

Steel shell

Steel shell

Concrete

Hub height (m)

32

40

50

58

77

Gear box

Helical par. shaft

Planetary

Planetary/he lical

Planetary

Planetary

Generator type

Induction

Induction

Synchronou s

Induction

Induction

Generator power (kW)

250/75

500/125

750

1,000/250

3,000/1,000

Weights
Machinery, turbine (tonne)
Total excl. foundation (tonne)

25

 

13
 

30

 

13.5
 

72

 

43

89

 

42

170

 

1,670

Specific weight
(kg/m2 swept area)

21

13

23

19

34

Conclusion

It is now 20 years since the start of the modern development of wind power. As of January 1996, the world total of installed wind power had passed 5,000 MW, and it is increasing by about 30% per year. It is an important time in the development of the wind power market, when siting difficulties must be solved and design improvements are leading to more cost-effective solutions. It will be interesting to follow the development of turbine design and improvements in the economics over the coming years.


For more information contact the CADDET Swedish National Team in Stockholm.

The CADDET Renewable Energy Newsletter is a quarterly magazine published by the CADDET Centre for Renewable Energy at ETSU, UK.

The articles published in the Newsletter reflect the opinions of the authors. They do not necessarily reflect the official view of CADDET.

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Pauline Toole, Editor, CADDET Centre for Renewable Energy, ETSU, Harwell, Oxfordshire OX11 0RA, United Kingdom. Tel: +44 1235 432968, Fax: +44 1235 433595.