3.6 Characteristic wind turbine data
This section compares characteristic data of different commercial wind turbines available in the past 10 years in Germany [27]. The data base comprises approx.
300 wind turbine types with a rated power above 30 kW for grid-connected opera- tion. In the diagrams, the discussed characteristic data is mostly plotted against the rated power or the rotor diameter since these two attributes characterize best the wind turbine size.
Wind turbine size has developed rapidly in the past 20 years, as discussed in chapter 1. Fig. 3-63 shows the growth of grid-connected wind turbines in these two decades. The increase in the rated power by the factor of 10 is an exceptional success in the area of mechanical engineering. In the past, a comparable stimu- lated development occurred only in the fields of computer and information tech- nology.
Since the 1990s, rotor diameter has grown by a factor of 8, the hub height has increased by a factor of 5.
Looking at the rated power versus the rotor diameter in Fig. 3-64, site-related influences have to be taken into account. The wind turbine should have its best- efficiency point close to the wind speed of maximum energy density, cf. chapter 4.
Wind turbines designed for coastal sites with a higher mean wind speed already achieve the same rated power with a smaller swept rotor area which results in a higher area-specific power (ratio of rated power and swept rotor area) of up to 520 W/m² producing the upper limiting curve. The lower limiting curve of 290 W/m² represents the design with a bigger rotor suitable for inland sites with a lower mean wind speed. For example, the 2 MW wind turbine MM82 of the com- pany REpower with a rotor diameter of 82 m, designed for inland sites has an area-specific capacity of 378 W/m², whereas its sister machine MM70 with the same rated power but designed for the windy coastal sites reaches 520 W/m2 due to the smaller rotor of 70 m.
0 1.000 2.000 3.000 4.000 5.000
1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004
Nennleistung in kW .
0 25 50 75 100 125
Rotordurchmesser in m .
Nennleistung Durchmesser
D = 15 m P = 55 kW H = 25 m
D = 20 m P = 75 kW H = 30 m
D = 30 m P = 300 kW H = 40 m
D = 45 m P = 600 kW H = 60 m
D = 70 m P = 1.500 kW H = 80 m
D = 125 m P = 5.000 kW H = 120 m
Rated power in kW Rotor diameter in m
Diameter
Power 0
1.000 2.000 3.000 4.000 5.000
1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004
Nennleistung in kW .
0 25 50 75 100 125
Rotordurchmesser in m .
Nennleistung Durchmesser
D = 15 m P = 55 kW H = 25 m
D = 20 m P = 75 kW H = 30 m
D = 30 m P = 300 kW H = 40 m
D = 45 m P = 600 kW H = 60 m
D = 70 m P = 1.500 kW H = 80 m
D = 125 m P = 5.000 kW H = 120 m
0 1.000 2.000 3.000 4.000 5.000
1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004
Nennleistung in kW .
0 25 50 75 100 125
Rotordurchmesser in m .
Nennleistung Durchmesser
D = 15 m P = 55 kW H = 25 m
D = 20 m P = 75 kW H = 30 m
D = 30 m P = 300 kW H = 40 m
D = 45 m P = 600 kW H = 60 m
D = 70 m P = 1.500 kW H = 80 m
D = 125 m P = 5.000 kW H = 120 m
D = 15 m P = 55 kW H = 25 m
D = 20 m P = 75 kW H = 30 m
D = 30 m P = 300 kW H = 40 m
D = 45 m P = 600 kW H = 60 m
D = 70 m P = 1.500 kW H = 80 m
D = 125 m P = 5.000 kW H = 120 m
Rated power in kW Rotor diameter in m
Diameter
Power
Fig. 3-63 Size and power of commercially produced wind turbines over time (cf. Fig. 1-1)
0 500 1.000 1.500 2.000 2.500 3.000 3.500 4.000 4.500 5.000
0 20 40 60 80 100 120
Rotordurchmesser in m
Nennleistung in kW
0 20 40 60 80 100 120 Seewind 22/110
REpower MM70
290 W/m2 520 W/m2
REpower MM82 E70, 2,3 MW
581 W/m2 5000
4500 4000 3500 3000 2500 2000 1500 1000 500 0
Rated powerin kW
Rotor diameter in m
0 20 40 60 80 100 120 Seewind 22/110
REpower MM70
290 W/m2 520 W/m2
REpower MM82 E70, 2,3 MW
581 W/m2 5000
4500 4000 3500 3000 2500 2000 1500 1000 500 0
Rated powerin kW
Rotor diameter in m Fig. 3-64 Rated power versus rotor diameter
3.6 Characteristic wind turbine data 108
Another characteristic number of the wind turbines which changed with the increasing turbine size are the mass of nacelle and rotor. As discussed in relation to Fig. 3-62 already, lightweight design reduced the required mass compared to the values calculated according to the similarity laws. In addition, Fig. 3-65 shows the area-specific nacelle mass, i.e. the ratio of nacelle mass and swept rotor area.
A temporal resolution of the data reveals that with the years the gradient of the regression line was reduced. It can be concluded that due to the gained know-how and the further development of the (computer-aided) design methods a specific weight reduction was attained despite the growing wind turbine size. Nevertheless, the values spread widely, because most of the manufacturers supply for the same rated power a “coastal type” with a smaller and a “inland type ” with a bigger rotor diameter, as mentioned before.
Fig. 3-66 shows the mass-specific torque (ratio of rotor torque and nacelle mass) versus the rotor diameter used to discuss the increasing power density of the wind turbines. The torque is calculated from rated power and maximum rotor speed. With larger rotor diameters, it increases not only due to the growing rated power but also due to smaller rotor speed (limiting criterion from maximum blade tip speed). There is a significant increase of the specific torque with the years; in 1996 the range covered 5-10 Nm/kg whereas in 2002 it reached 15-20 Nm/kg for the MW class wind turbines of more than 60 m rotor diameter. This shows that the stress gets closer to the admissible material strength, the design is more stress- optimized (instead of high safety factors in the beginning) and also that new materials are applied. Moreover, the power density increases if generators and gearboxes are more compact because of e.g. better cooling and advanced power electronics. The wind turbines are becoming (specifically) lighter and more cost- effective.
0 5 10 15 20 25 30 35 40
0 20 40 60 80 100 120
Rotordurchmesser in m
spezifische Gondelmasse in kg / m2
1996
1999
2002
0 5 10 15 20 25 30 35 40
0 20 40 60 80 100 120
Rotordurchmesser in m
spezifische Gondelmasse in kg / m2
1996
1999
2002
Rotor diameter in m
Specific nacelle mass in kg/ m²
0 5 10 15 20 25 30 35 40
0 20 40 60 80 100 120
Rotordurchmesser in m
spezifische Gondelmasse in kg / m2
1996
1999
2002
0 5 10 15 20 25 30 35 40
0 20 40 60 80 100 120
Rotordurchmesser in m
spezifische Gondelmasse in kg / m2
1996
1999
2002
Rotor diameter in m
Specific nacelle mass in kg/ m²
Fig. 3-65 Specific nacelle mass versus rotor diameter
0 5 10 15 20 25
0 20 40 60 80 100 120 140
Rotordurchm esser in m
spezifisches Drehmoment in Nm/kg
1996 1999 2002 Linear (2002) Linear (1996)
Rotor diameter in m
Specific torque in Nm/kg
0 5 10 15 20 25
0 20 40 60 80 100 120 140
Rotordurchm esser in m
spezifisches Drehmoment in Nm/kg
1996 1999 2002 Linear (2002) Linear (1996)
Rotor diameter in m
Specific torque in Nm/kg
Fig. 3-66 Specific torque versus rotor diameter
The energy yield of wind turbines is basically site-specific. In order to get compa- rable values, the reference yield is introduced and defined by the wind conditions specified in the German Renewable Energy Sources Act (EEG) from April 2002 as follows [28]:
x Mean wind speed in 30 m height: 5.5 m/s
x Roughness length z0: 0.1 m
x Wind frequency distribution according to Rayleigh: k = 2 The law establishes a virtual average German site with approx. 1,700 annual full load hours as the basis for wind turbine comparison. This is equivalent e.g. to moderately windy sites in the German federal state of Brandenburg. Fig. 3-67 shows that with the increasing turbine size (i.e. with the years) the area-specific reference yield (ratio of reference yield and swept rotor area) grew by more than 50%, from approx. 600 kWha/m² to approx. 1000 kWha/m². The spreading of the values depends not only on turbine type and manufacturer but also per type on the different available hub heights, see section 3.4. The achieved increase is mainly due to the growing hub heights providing better wind conditions for the turbine operation.
3.6 Characteristic wind turbine data 110
0 200 400 600 800 1.000 1.200
0 500 1.000 1.500 2.000 2.500 3.000
Nennleistung in kW
Flọchenertrag in kWh / m2
Coastal sites (smaller rotors)
Inner land sites (bigger rotors)
0 500 1000 1500 2000 2500 3000 Rated power in kW
1200
1000
800
600
400
200
0 Specific referenceyield in kWha/m²
0 200 400 600 800 1.000 1.200
0 500 1.000 1.500 2.000 2.500 3.000
Nennleistung in kW
Flọchenertrag in kWh / m2
Coastal sites (smaller rotors)
Inner land sites (bigger rotors)
0 500 1000 1500 2000 2500 3000 Rated power in kW
1200
1000
800
600
400
200
0
Specific referenceyield in kWha/m² Coastal sites (smaller rotors)Coastal sites (smaller rotors)
Inner land sites (bigger rotors) Inner land sites (bigger rotors)
0 500 1000 1500 2000 2500 3000 Rated power in kW
1200
1000
800
600
400
200
0 Specific referenceyield in kWha/m²
Fig. 3-67 Area specific annual reference yield versus rated power
Considering in Fig. 3-68 the best efficiency of the wind turbines, i.e. the power coefficient cP.max , drawn from the power curves measured for type approval, a wide spreading of the values can be observed. The reason for this is the broad operating range of wind turbines. Hence, the manufacturers optimize the entire machine for a wide range of relatively high efficiency. This is needed especially for inland sites in order to maximize the annual energy yield: on one hand the very frequent weak winds have to be harvested efficiently, but on the other a good effi- ciency should also bring a high yield share from rarer strong winds (P~v³!).
The final consideration, Fig. 3-69 discusses available commercial wind turbines concerning the two classical concepts of power limitation: stall and pitch. It shows a clear tendency to depart from a domination of stall-controlled turbines (without blade pitching) until the mid 1990s to a preference for pitch-controlled wind tur- bines evident in today’s MW class turbines. In Germany, hardly any stall wind turbines have been recently installed, mainly due to strict grid codes, cf. chapter 14. In the first half of 2005, e.g. only pitch-controlled wind turbines were erected, of which 10% had an active stall control.
But in other countries with a different market situation and more restricted transport and erection conditions, there is a high demand for the robust and well- proven stall turbines. Even the company ENERCON, a classical manufacturer of gearless pitch-controlled wind turbines, now tests a 20 kW prototype with power limitation by stall. And also the 5 kW wind turbine Aerosmart 5, Fig. 3-57 left, re- cently developed for stand-alone systems and developing countries, has a down- wind rotor with stall control.
0 0,1 0,2 0,3 0,4 0,5 0,6
0 500 1000 1500 2000 2500
Nennleistung in kW
Bestwirkungsgrad cP.max
0,6
0,5
0,4
0,3
0,2
0,1
0 Maximum power coefficient cP.max
0 500 1000 1500 2000 2500 Rated power in kW
0 0,1 0,2 0,3 0,4 0,5 0,6
0 500 1000 1500 2000 2500
Nennleistung in kW
Bestwirkungsgrad cP.max
0,6
0,5
0,4
0,3
0,2
0,1
0 Maximum power coefficient cP.max
0 500 1000 1500 2000 2500 Rated power in kW
Fig. 3-68 Maximum power coefficient cP.max of a wind turbine versus rated power (from power curve measurements)
0 10 20 30 40 50 60 70 80
Number of available W. T. types
1991 1993 1995 1997 1999 2001 2003 2005
Rated power > 150 kW
Pitch
Stall
0 10 20 30 40 50 60 70 80
Number of available W. T. types
1991 1993 1995 1997 1999 2001 2003 2005
Rated power > 150 kW
Pitch
Stall
Fig. 3-69 Number of available stall and pitch wind turbine types on the German market [27]
3.6 Characteristic wind turbine data 112
References
[1] The editors are grateful for the photos and figures provided by wind turbine manufac- turers and suppliers.
[2] Kửrber F., Besel G. (MAN), Reinhold H. (HEW): Messprogramm an der 3MW- Windkraftanlage GROWIAN (Test program on the 3 MW wind turbine GROWIAN), Report on the research project 03E-4512-A of the German Federal Ministry of Tech- nology, München, Hamburg 1988
[3] According to information of Sydkraft; Malmử (S) 1991
[4] N.N.: What we have learnt about wind power at Maglarp and Nọsudden, Statens ener- gieverk, Stockholm (S) 1990
[5] Wachsmuth R. (MBB): Rotorblatt in Faserverbundbauweise für Windkraftanlage AEOLUS II (Rotor blade in fibre composite construction for the wind turbine AEOLUS II), Report on the research project 032-8819-A/B in the status report wind energy 1990 of the German Federal Ministry of Technology, KFA Jülich (Ed.) 1990 [6] Hau E.: Windkraftanlagen - Grundlagen, Technik, Einsatz, Wirtschaftlichkeit (Wind
power plants – Basics, technology, application and economics), Springer-Verlag, Berlin, Heidelberg, New York 1988 / 2003
[7] Maurer J.: Wind turbinen mit Schlaggelenkrotoren, Baugrenzen und dynamisches Verhalten (Wind turbines with a flapping hinge rotor, design limits and dynamic characteristics), PhD thesis, TU Berlin; VDI Reports, series 11, No. 173, Düsseldorf 1992
[8] Wortmann F.X. (Institut für Aerodynamik und Gasdynamik der Uni Stuttgart): Neue Wege zur Windenergie (New approaches to wind energy), Imprint of the DFG series:
Forschung in der Bundesrepublik Deutschland - Beispiel, Kritik, Vorschlọge, Verlag Chemie, Weinheim 1983
[9] Person M.: Zur Dynamik von Wind turbinen mit Gelenkflỹgeln - Stabilitọt und erzwungene Schwingungen von Ein- und Mehrflüglern (On the dynamics of wind turbines with flapping hinge blades – stability and forced vibrations of one and multi- bladed turbines), PhD thesis at the Institut für Luft- und Raumfahrt of TU Berlin, VDI Fortschritt-Berichte (Progress reports) Series 11, No. 104, Düsseldorf 1988
[10] Franke, J.B.: Erarbeitung eines Konzeptes zur Berechnung der Lebensdauer von Getriebeverzahnungen unter Berỹcksichtigung der Betriebszustọnde von Windenergieanlagen (A concept for the lifetime calculation of the gear tooth system considering the operating conditions in wind turbines), TU Berlin/Germanischer Lloyd WindEnergie GmbH, 2004
[11] DUBBEL, Beitz W. und Küttner K.-H.: Taschenbuch für den Ingenieur (Handbook of Mechanical engineering), Springer-Verlag Berlin, Heidelberg, New York, 2002 [12] Deutsches Institut fỹr Normung: DIN 3990, Tragfọhigkeitsberechnung von Stirnrọdern
(Calculation of load capacity of spur gears), Beuth-Verlag, Berlin, 1987
[13] International Organization of Standardisation (ISO): Calculation of load capacity of spur and helical gears, ISO 6336, Genf, 1996
[14] Boiger, P.: Die Aerogear-Baureihe soll für mehr Sicherheit und Ruhe bei Getrieben sorgen (The Aerogear product line will improve safety and reduce noise of gearboxes), Windkraft Journal, 2002
[15] Germanischer Lloyd WindEnergie GmbH: Richtlinien für die Zertifizierung von Windkraftanlagen I...IV (Guideline for the Certification of Wind Turbines), Hamburg 1993 to 2003
[16] Haibach, E.: Betriebsfestigkeit, Verfahren und Daten zur Bauteilberechnung (Fatigue analysis, procedure and data for component desig ), VDI-Verlag, 1989
[17] Schlecht, B., Schulze, T., Demtrửder, J.: Modelle zur Triebstrangsimulation von Multi- Megawatt Windenergieanlagen (Models for the drive train simulation of Multi-MW
wind turbines), Tagungsband Dresdener Maschinenelemente Kolloquium 2003, S.
351-362, Verlagsgruppe Mainz, Aachen, 2003
[18] Thửrnblad, P.: Gears for Wind Power Plants, 2nd Int. Symposium on Wind Energy Systems, Amsterdam, 1978
[19] N.N.: Betriebsanleitung für die Allgaier Windkraftanlage (Operating manual for the Allgaier wind turbine) System Dr. Hütter, Type WE 10/G6, Uhingen
[20] Institut für Solare Energieversorgungstechnik e. V. (ISET): EU-Projekt NEW ICETOOL (deutsches Teilprojekt), http://www.iset.uni-kassel.de/icetool/
[21] BINE Informationsdienst: Blitzschutz für Windenergieanlagen (Lightning protection for wind turbines), Projektinfo 12/00, Fachinformationszentrum Karlsruhe, http://bine.info
[22] Fửrdergesellschaft Windenergie e.V. und Bundesministerium fỹr Wirtschaft und Technologie (Hrsg.): Blitzschutz von Windenergieanlagen(Lightning protection for wind turbines), Abschlussbericht, BMWi-Forschungsvorhaben 0329732, Juli 2000 [23] Deutsches Windenergie-Institut (DEWI): Studie zur aktuellen Kostensituation 2002
der Windenergienutzung in Deutschland (Study on the costs of wind energy utilization in 2002 ), Wilhelmshaven 2002
[24] Germanischer Lloyd WindEnergie GmbH: Richtlinie für die Zertifizierung von Condition Monitoring Systemen für Windenergieanlagen (Guideline for the Certification of Condition Monitoring Systems for Wind Turbines), Edition 2003 [25] Heilmann, C., Liersch, J., Melsheimer, M.: Rotorunwuchten sind vermeidbar (Rotor
unbalance is avoidable), Sonne, Wind und Wọrme 4/2006
[26] Huò G. (MAN): Modifizierung des Anlagenkonzepts WKA-60 im Hinblick auf eine Leistungssteigerung, Landaufstellung und eine Verbesserung der Wirtschaftlichkeit, (Report on the concept modifications of the WKA-60 wind turbine concerning performance improvement, onshore installation and improvement of cost- effectiveness) Report on the research project 032-8824-A in the status report wind energy 1990 of the German Federal Ministry of Technology, KFA Jülich (Ed.) 1990 [27] Bundesverband WindEnergie e.V., BWE Service GmbH (Hrsg.): Windenergie 2005
Marktübersicht (Wind energy market 2005), and previous editions starting 1996 [28] Erneuerbare-Energien-Gesetz (EEG) der Bundesregierung (German Renewable
Energy Sources Act (EEG)), 2000, 2003, 2004 http://www.erneuerbare-energien.de/
[29] Kửrber, F.: Baureife Unterlagen fỹr GROWIAN (Documentation for the construction of GROWIAN), Final report on the research project of the German Federal Ministry of Technology, München, 1979
R. Gasch and J. Twele (eds.), Wind Power Plants: Fundamentals, Design, Construction 114 and Operation, DOI 10.1007/978-3-642-22938-1_4, © Springer-Verlag Berlin Heidelberg 2012
4 The wind