LECTURE 18WIND POWER

SYSTEMS

ECE 371Sustainable Energy Systems

1

HISTORICAL DEVELOPMENT

The first wind turbine used to generate electricity was built by La Cour of Denmark in 1891

2

HISTORICAL DEVELOPMENT

Diameter = 23 m, P = 18 kW, 4 Blades

The electricity was used to electrolyze water

The produced hydrogen was used for gas lights in the local schoolhouse

He was 100 years ahead of his time3

HISTORICAL DEVELOPMENT

In the U.S. the first wind-electricity system was build in late 1890s

In 1941, one of the largest wind-powered systems went into operation in Vermont to produce 1.25 MW from a 53-meter diameter, two bladed prop (Smith-Putnam Wind Turbine)

4

HISTORICAL DEVELOPMENT

5

HISTORICAL DEVELOPMENT

It catastrophically failed in 1945 due to a 25 mph wind, while before it had withstood winds as high as 115 mph

The activity in this area died until 1970s

Thousands of wind turbines were installed in California from mid-1970s through 1985

Due to oil crisis of 1970s and tax incentives6

HISTORICAL DEVELOPMENT

After that the tax credits were terminated and the industry was wiped out in the US until early 1990s

Meanwhile, wind turbine technology development continued in Europe Germany Spain Denmark (Vestas)

7

HISTORICAL DEVELOPMENT

8

HISTORICAL DEVELOPMENT

The following figure shows the global installed wind power capacity

By the end of 2016, the global installed capacity was 430 GW

9

HISTORICAL DEVELOPMENT

The countries with most installed wind capacity are shown below (as of beginning of 2012)

By the end of 2016, the U.S. installed capacity was 82 GW

10

HISTORICAL DEVELOPMENT

The fraction of electricity generated from wind is shown below (Now Denmark is 41.2%)

11

TYPES OF WIND TURBINES

One way of classifying wind turbines is in terms of the axis around which the turbine blades rotate

Horizontal axis wind turbines (HAWT) Upwind Downwind

Vertical axis wind turbines (VAWT) Darrieus, developed in 1920s by a French engineer

12

TYPES OF WIND TURBINES

13

Nacelle

noun 1. the enclosed part of an airplane, dirigible, etc.,

in which the engine is housed or in which cargo or passengers are carried.

2. the car of a balloon.

14

TYPES OF WIND TURBINES

Advantages of VAWT Don’t need yaw control Equipment in nacelle are at ground level Tower and blades are light weight and inexpensive

Disadvantages of VAWT Blades are close to ground where wind speeds are low At low wind speeds they have low starting torque At high speeds they can’t spill power to protect

equipment15

TYPES OF WIND TURBINES

Advantages of downwind turbines Wind controls the yaw, so it naturally orients itself

Disadvantages of downwind turbines Wind shadowing of a blade swings behind the tower

it encounters a brief period of reduced wind, which causes the blade to flex This can cause blade fatigue, increased blade noise, and

reduced power

16

TYPES OF WIND TURBINES

Advantages of upwind turbines Operate more smoothly Deliver more power

Disadvantages of upwind turbines Complex yaw control system

Most modern wind turbines are upwind with 3 blades Smoother operation Quieter

17

TYPES OF WIND TURBINES

Key components of WTG is shown below

18

ROTORS

At the beginning of the 21st century most turbines were rated at Capacity of 1-2 MW Hub height of 50-80 m Blade diameter of 80-100 m

A decade later the largest machines for off-shore applications are rated for 7 MW

19

ROTORS

20

ROTORS

To understand wind turbine performance, extraction power from the wind by the rotor blades needs to be looked at

To do this, we need to consider a simple airfoil cross section

21

ROTORS

An airfoil, whether it is the wing of an airplane or the blade of a windmill, takes advantage of the Bernoulli’s principle to obtain lift

Air moving over the top of the airfoil has a greater distance to travel before it can rejoin the air that took the short cut under the foil Air pressure on top is lower than that under the

airfoil This creates the lifting force that holds an airplane

up or wind turbine blade to rotate22

ROTORS

23

ROTORS

A rotating turbine blade sees air moving toward it not only from the wind itself, but also from the relative motion of the blades as it rotates This results in the two wind vectors add up to a

resultant vector moving across the airfoil at the correct angle to obtain the lift that moves the rotor

Since the blade is moving much faster at the tip than near the hub, the blade must be twisted along its length to keep the angles correct

24

ROTORS

The angle of attack is the angle between the airfoil and the wind

Increasing the angle of attack improves lift at the expense of increased drag

But increasing the angle of attack too much can result in a phenomenon known as stall

When a wing stalls, air flow over the top no longer sticks to the surface, and the resulting turbulence destroys lift

25

ROTORS

26

ROTORS

Power delivered by the wind turbine increases with increasing windspeed

At some point, the generator reaches its maximum capacity

Must shed some of the wind’s power

27

ROTORS

28

ROTORS

Three approaches are common for large machines

Passive Stall Control

Active Pitch Control

Active Stall Control

29

ROTORS

For stall-controlled machines, the blades are designed to reduce power for excessive winds

Stall Controlled Machines- Due to aerodynamics of rotor blades The blades are fixed on the rotor and pitch is fixed. Blade aerodynamics are designed such that lift is reduced as

windspeed increases Sacrifices power at low windspeed - less than 1 MW size

30

ROTORS

Active Pitch Control - Due to rotor blades rotationElectronic system monitors generator output power If it exceeds the rated value, pitch of the blades is

adjusted Hydraulic system slowly rotates the blades

Angle of attack is reduced at high wind speeds to reduce lift

Once the rotor is stopped, a brake locks the rotor shaft

31

ROTORS

Active Stall Control - Due to rotor blades rotationElectronic system monitors generator output power If it exceeds the rated value, pitch of the blades is

adjusted Hydraulic system slowly rotates the blades

Angle of attack is increased at high wind speedsStall is inducedOnce the rotor is stopped, a brake locks the rotor shaft

32