1

Historical Development

of Wind Turbines

Svein Kjetil Haugset, 2007

2

First use of wind - sails

• In use for 6000 years• ”Catching” the wind in a sail• Generating a drag force, D

– due to pressure differences– parallel to the wind

• Drag force, D, on the sail:

v1 usail

v3

phigh plow

2

1

1w

2w v u , relative speed

, area of the sail

, drag force coefficient, unity

D

D

D a c

a

c

3

“Sailing” the mills in Mesopotamia

• First historic record from 1700BC in Mesopotamia.

• Afghan records 700AD show the title: “Millwright” as a common one.

• Mill-ruins in Iran and Afghanistan shows widespread use

• Known as “Persian wind mill”:– purely drag devices, using “sails”– fixed direction – slow rotating (slower than the wind)– poor efficiency, less than 10%

4

”Sailing” the mills elsewere

• Chinese drag-type mills– First record in 1219 A.D., possibly much

older– No screen – the sails were adjusting to

the wind direction– Could be used in all direction

• Recent design:– Savounius-type turbines– Cup aneometers

• Said to be the most “re-invented” turbine.....

5

Turbines in medieval Europe

• First record in Europe in 1185, Yorkshire.

• The “Windmill Psalter” from Canterbury, 1270, with picture.

• Horizontal axed – “sails” does not move parallel with the wind, but perpendicular to the wind.

• Lift-force is dominant: – no longer “sails” but “wings”

• Wind speed is no longer the limitation for the rotational speed.

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Drag-type vs. lift-type turbines

• Drag force: • Lift force:

2

1 , relative speed

, area

, drag force coefficient

1 w2

w v u

D

D

ac

D a c

2 21

2

v u

, lift force coefficient

1 w2

w

L

L

c

L a c

v1 usail w

axis of rotation

D

v1

uwing

axis of rotation

wu L

7

First industrial revolution?

• Alongside watermills, the only source of mechanical power– 3-7 kW out-put, depending on size and wind conditions

• Used for grinding

• Long lasting design:– Great variation in structural design and control mechanisms but the overall

principle stayed the same till the 18th century.

• By the 14th century, it was widely used in whole Europe

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Fortunes to the Netherlands

• Need for drainage lead to new development

• The new design featured:– a shaft to lead the power to

ground level.– possibility to link several mills

together– gradually improvement in the wing

design.

• Gave the opportunity for new uses

9

Variations in structural design

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Scientific research

• Design done by craftsmen for 3400 years

• John Smeaton - first wind scientist?– Measuring efficiency, CP = 0,28

– Designed the twisted blade.

• The modern turbine is “ready”:1. Chambered leading edge (airfoil)

2. Blade-beam at 25% of airfoil length

3. Non-linear twist of airfoils

• 200 years of optimizing still to go!

11

Wild West Wind

• Fan type turbines in USA:– Halladay introduced in 1854– Aermotor ca 1870

• Autonomous system– Turned after the wind– Turned out of the wind at high

speeds

• Higher speed and efficiency

• Widely used– From 1854-1970: 6 million– Still in use to day

12

Wind goes electric

• First large scale electric wind turbine in 1888: Charles F. Brush

– Ø 17 m – 12 kW– step-up gearbox (50:1) – 10 / 500 r.p.m.

• First Danish electrical wind turbine in 1891: Poul La Cour

– low solidity (ratio of area)– airfoil shaped blades– higher rotational speed– 25 kW

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Modern theory is developed

• Research on propellers and airfoils– NACA (later NASA) in USA and Göttinger in Germany– Airfoil and propeller theory was developed– Modern wind turbines: a spin-off from war-industry (?)

• Albert Betz:– Worked on the theoretical limit of wind turbines: the Betz’ limit.

• An ideal turbine, independent of design, will only be able to extract 59,3% of the available kinetic energy in the wind.

– Was important in developing the Blade Element Momentum Methode.• Ludvig Prandt’l:

– Simplified the complex analysis of Betz.– Developed Prandt’l Tip Loss Factor:

• Theoretical model for the loss in lift at the tip of a turbine blade

• The theoretical foundation for the modern turbine was made!

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Various attempts:

Smith-Putam, 1941, USA:

•1.25 MW, 175 foot

•2 steel blades (16 tons)

•Down-wind type

•Destroyed after less than 1000 hours

Gedser Mill, 1960s, DK:

•200 kW

•3 glass fibres blade

•Up-wind type

•Basis for the Danish concept

Hutter, 1968, D:

•2 glass fibres and plastic blades

•Shedding aerodynamic loads

•4000 hours before project was ended

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The Danish Concept

• Three bladed • Up-wind• Dimensioned to withstand gusts• AC – generators• Constant rotational speed• Automatic yawing (turning after the wind)• Stall controlled.

• Great commercial success in the 80s– The 55 kW sold over 10.000– Size gradually grew– VESTAS gained a leading position in the marked

16

Growing in the wind

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What now?

• Potential for improving:– transmission, mechanical gears is the Achilles heal of the turbine

– lighter and stronger materials in the blades

– individually pitched (regulated) blades

– lower sound level

– decrease tip-losses

– making installations and maintenance more efficient

– CUTING COSTS

• Moving the turbines off-shore– floating installations no one can see (and would not protest against)

• Larger turbines– 5 MW is built, 7 MW is discussed.

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What have we learned?

• Wind turbines is one of the oldest energy sources we know of

• The development of modern type turbines has taken nearly 900 yrs

• Have had great impact on the economy in various periods

• The modern turbine was made 250 yrs ago

• Basic theory only available in less than 90 yrs

• Still lost of things to do.......