Feed Laws

Reviews of Engineering & Technical Books

January 19, 2004
Paul Gipe

Wind Power Plants: Fundamentals, Design, Construction and Operation by R. Gasch, J. Twele

The book, edited by Robert Gasch, began as course notes for Gasch's popular course on wind turbine design for engineering students at the Technische Universität in Berlin. Many of the book's 15 authors are either graduates of or were members of TU-Berlin's Aerospace Institute. Though professor Gasch has retired, many of the other authors work today in the German wind industry.

Wind Power Plants originally appeared in German as Windkraftanlagen. The literal translation of windkraftanlagen is "wind power plants." However the term wind power plant has a different meaning in English than in German, that is, a collection or array of wind turbines. Windkraftanlagen is more akin to "wind generator" or "wind turbine" in English.

Disclosure: I initially proposed this book to MIT Press but later withdrew my participation. It was subsequently published in Germany.

While it's difficult to pick one of the new engineering texts (there are two by John Wiley & Sons alone) as "best in the class," Gasch's book is clearly one of the best. Wind Power Plants includes numerous illustrations and drawings found nowhere else. This is in part due to the authors' location in northern Europe where the modern wind industry has its roots, and the authors long association with the early wind industry.

The introductory chapter alone should be required reading for anyone entering the renewables field. It sets the stage for why wind energy is both important, and why wind is not the sole solution. Unlike many contemporary books on energy Wind Power Plants opening chapter looks squarely at population growth and growth in consumption of electricity. And on both accounts the USA compares poorly with other developed countries. The USA--the world's third most populous country with one of the world's highest per capita consumption of electricity--has a population growth rate rivaling that of China, and the USA's growth in consumption is nearly three times that of Germany. In fact Germany cut its per capita consumption from 1985 through 1995. Sobering. I'd go so far as to say that this chapter should be widely circulated among environmentalists, energy planners, and politicians in North America.

The introductory chapter also provides a useful summary of the difference between environmentally-driven markets for wind energy and energy-driven markets, as well as a brief explanation of Electricity Feed Laws such as used in Germany and Spain.

In a sign-of-the-times, this English-language version drops the chapter on vertical-axis wind turbines, adding instead a chapter on off-shore wind.

Wind Power Plants is one the few if not the only engineering text with a chapter on wind pumping. And in the chapter on electrical generators is a section not only describing battery-charging wind turbines--the neglected sibling of professional designers--but also electrical resistance heating as in the University of Massachusetts Wind Furnace.

The principal weakness of the book is the absence of any discussion of siting issues, such as noise or aesthetics.

Wind Power Plants: Fundamentals, Design, Construction and Operation by R. Gasch, J. Twele, et al., 385 pages, 245 x 170 MM (~6 x 9 inches) paper: ISBN 3-934595-23-5 €39; cloth: ISBN 1-902916-37-9 €60; 2002. Available from both James & James, 8-12 Camden High Street, London, NW1 0JH, United Kingdom, Phone: +44 20 7387 8558, Fax: + 44 20 7387 8998,,; and Solarpraxis, Torstrasse 177, Berlin, D-10115, Germany, Phone: 49 30 726 296 300, Fax: 49 30 726 296 309 ,,


Table of Contents


1 Introduction to wind energy

1.1 Wind energy at the beginning of 2002

1.2 The demand for electricity

1.3 Energy policy and governmental instruments

1.4 Technological development

2 Historical background on windmills

2.1 Vertical axis windmills

2.2 Horizontal axis windmills

2.2.1 From post mills to American farm windmills

2.2.2 Technological innovations

2.2.3 Beginning and end of the wind power era in the Occident

2.3 The physics of utilizing wind energy

2.3.1 Wind power

2.3.2 Drag devices

2.3.3 Lift devices

2.3.4 Comparison of drag and lift devices


3 Wind turbines - design and components

3.1 Brief description of different wind turbines

3.1.1 Research prototypes

3.1.2 The Danish concept

3.1.3 Development on the German market

3.1.4 Stand-alone power systems

3.2 Main issues regarding the design of a wind turbine

3.2.1 Applications and supervisory systems

3.2.2 Design wind speed

3.2.3 Principal data

3.3 Rotor

3.4 Rotor blade design and materials

3.5 Hub and blade attachment

3.6 Design of the drivetrain and the bed plate

3.7 Yawing

3.8 Overs peed control and secondary protection systems

3.9 Limiting power output

3.10 Tower and foundation


4 The wind

4.1 Wind sources

4.1.1 Global Circulations

4.1.2 Local compensation winds

4.2 Surface wind

4.2.1 The sources of the surface wind

4.2.2 Vertical wind speed gradient and surface roughness

4.2.3 Obstacles on the ground

4.3 Wind measurements and their evaluation

4.3.1 Measuring the wind

4.3.2 Analysis, wind histograms,yield prediction

4.4 Idealised wind histograms- Rayleigh and Weibull distribution

4.5 Site evaluation


5 Wind turbine dimensioning according to Betz and Schmitz

5.1 How much power can be extracted from the wind?

5.1.1 Rankine-Froude theorem

5.2 Aerofoil theory

5.3 Air flow conditions and aerodynamic forces at the rotating blade

5.3.1 Triangle of velocities

5.3.2 Aerodynamic forces at the rotating blade

5.4 The Betz optimum dimensioning

5.5 Losses

5.5.1 Profile losses

5.5.2 Tip losses

5.5.3 Losses due to wake rotation

5.6 The Schmitz dimensioning taking into account the rotational wake

5.6.1 Losses due to wake rotation

5.7 Wind turbine designing in practice


6 Calculation of performance characteristics and partial loads behaviour

6.1 Method of calculation (blade element method)

6.2 Dimensionless presentation of the characteristic curves

6.3 Dimensionless characteristic curve of a turbine with a high tip speed ratio

6.4 Dimensionless characteristic curves for turbines with a low tip speed ratio

6.5 Turbine performance characteristics

6.6 Stream conditions

6.6.1 Turbines with high vs low tip speed ratio: A summary

6.6.2 Apparent wind at a turbine with a lowtip speed ratio of design

6.6.3 Apparent wind at a turbine with a high tip speed ratio of design

6.7 Behaviour of turbines with high tip speed ratios during change of pitch

6.8 Extending the calculation method

6.8.1 The range of (cascade effects, tip losses)

6.8.2 The range of (the Glauert empirical formula)

6.8.3 The profile drag

6.8.4 The extended iteration

6.9 Limits of the blade element theory and advanced calculation methods

6.9.1 Lift distribution and three-dimensional effects

6.9.2 Dynamic stall


7 Structural loads and strength issues

7.1 Combined loading

7.2 Loads on the blades of wind turbines

7.2.1 Steady, quasi-static loads

7.2.2 Short-term loading from gusts

7.2.3 Short term loading due to centrifugal, gyroscopic and Coriolis forces during the yaw movement of the rotor

7.2.4 Braking processes

7.2.5 Cyclic loads due to blade weight

7.2.6 Cyclic forces due to tower dam or tower shadow

7.2.7 Skew winds, boundary-layer profile near the ground

7.3 Loads on nacelle and tower

7.4 Fatigue limits

7.5 Materials' strength

7.6 Standards, guidelines, regulations


8 Scaling wind turbines and rules of similarity

8.1 Application and limits of the theory of similarity

8.2 Bending stress

8.3 Tensile stress in the blade root resulting from centrifugal forces

8.4 Bending stress in the blade root due to weight

8.5 Change in the natural frequencies of the blade and in the frequency ratios


9 Wind pumping systems

9.1 Characteristic applications

9.2 Types of wind-driven pumps

9.3 The combined 9peration of wind turbine and pump

9.3.1 Reasonable combinations of wind turbines and pumps

9.3.2 Qua1itative comparison of wind pumping systems with a piston and a centrifugal pump

9.4 Dimensioning a wind pumping system

9.4.1 Dimensioning goal

9.4.2 Selection of the design rated windspeed

9.4.3 Dimensioning of wind pumping systems with a piston pump

9.4.4 Dimensioning of wind pumping systems with.acentrifugal pump


10 Electrical power generating systems

10.1 Basic concepts

10.1.1 The a.c. machine (dynamo) in stand-alone operation

10.1.2 Types of excitation and constructional designs

10.1.3 Synchronous a.c. machines (dynamo) in grid-connected operation

10.1.4 a.c. machines and their construction

10.2 The synchronous a.c. machine and its application

10.2.1 Battery chargers

10.2.2 Resistance heating with synchronous generators

10.2.3 Wind pumping system with electrical power transmission

10.2.4 Feeding local grids, stand-alone operation

10.2.5 Grid-connected operation

10.3 The induction machine and its application in wind turbines

10.3.1 Principle of operation

10.3.2 The Danish concept: Directly grid-connected induction generators

10.3.3 Variable-speed grid connection

10.3.4 Induction generators in local grids

10.3.1 Principle of operation

10.3.2 The Danish concept: Directly grid-connected induction generators :

10.3.3 Variable-speed grid connection

10.3.4 Induction generators in local grids


11 Controlling wind turbines

11.1 Goals of controlling

11.2 Types of control

11.3 .influencing the rotor

11.3.1 Turning the rotor out of the wind

11.3.2 Pitch towards feather

11.3.3 Pitch towards stall

11.4 Examples of simple control systems

11.4.1 Controlling turbines with a low tip speed ratio by using wind pressure

11.4.2 Controlling wind turbines with a high tip speed ratio by wind pressure


11.4.4 Passive control by aerodynamic forces


11.5 Examples of fast control systems

11.5.1 Grid-connected operation with the Danish concept

11.5.2 Variable-speed grid-connected operation with pitch regulation (slow pitch)

11.5.3 Fixed-speed operation with fast pitch

11.5.4 A comparison of concepts using different existing turbines

11.5.5 Other control concepts


12 Dynamic problems of wind turbines

12.1 Oscillations of nacelle and tower caused by imbalances

12.2 Oscillations of nacelle and tower due to the tower shadow

12.3 Blade oscillations

12.4 Oscillations of the drive train

12.5 Modelling issues


13 Offshore wind farms

13.1 Offshore environment

13.2 Offshore design requirements

13.3 Wind turbines

13.4 Support structures and marine installation

13.5 Grid connection and wind farm layout

13.6 Operation and maintenance

13. 7 Economics



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