WIND

ELECTRIC CONVERSION

Basic Questions for Wind System Design

Monitor speed, direction and temperature

Wind resource Evaluation

Components of WECS, their Functions

Operating characteristic speeds

Gear for turbine to generator speed

conversion

Energy Flow and Control in WECS

Generators

Basic questions for

Wind System Installation

• Is there enough wind ?

• Are tall wind towers allowed in your area?

• Do you have enough space?

• How much electricity do you need or want to produce?

• Do you want to connect to the utility grid or be grid-independent?

• Can you afford a wind energy system? 2

Basic questions for

Wind System Installation

• What does it take to install and maintain a system? Is there enough wind where you install it ?

• How much electricity do you need or want to produce?

3

Kinetic > Mechanical > Electric

Wind is created by the unequal

heating of the Earth’s surface by

the sun. Wind turbines convert

the kinetic energy in wind into

mechanical power that runs a

generator to produce clean

electricity.

4

5

Wind resources evaluation

• Apart from having a good wind turbine, the most

critical aspects for the success of investment in the

wind energy sector are (i) having a good site and

(ii) an accurate assessment of the wind resource at

the site over the season of active wind.

Wind Resource Monitoring consists of following

activities (i) Siting, (ii) Wind Monitoring

(iii) Wind Resource Mapping

6

On farm tower for Pumping Water

• One- to 10-kW turbines can be used in

applications such as pumping water.

• Wind-electric pumping systems can be

placed where the wind resource is the

best and connected to the pump motor

with an electric cable.

7

Turbine Component Function

Nacelle

Contains the key components of the wind turbine,

including the gearbox, yaw system, and electrical

generator.

Rotor blades Captures the wind and transfers its power to the rotor

hub.

Hub Attaches the rotor to the low-speed shaft of the wind

turbine.

Low speed shaft Connects the rotor hub to the gearbox.

Gear box

Connects to the low-speed shaft and turns the high-

speed shaft at a ratio several times (approximately 50

for a 600 kW turbine) faster than the low-speed shaft.

High-speed shaft

with mechanical

brake

Drives the electrical generator by rotating at

approximately 1,500 revolutions per minute (RPM).

The mechanical brake is used as backup to the

aerodynamic brake, or when the turbine is being

serviced.

Electric generator

Usually an induction generator or asynchronous

generator with a maximum electric power of 500 to

1,500 kilowatts (kW) on a modern wind turbine.

Yaw mechanism Turns the nacelle with the rotor into the wind using

electrical or other motors.

8

Electronic controller

Continuously monitors the condition of the wind

turbine. Controls pitch and yaw mechanisms. In

case of any malfunction (e.g., overheating of the

gearbox or the generator), it automatically stops

the wind turbine and may also be designed to

signal the turbine operator's computer via a modem

link.

Hydraulic system Resets the aerodynamic brakes of the wind turbine.

May also perform other functions.

Cooling system

Cools the electrical generator using an electric fan

or liquid cooling system. In addition, the system

may contain an oil cooling unit used to cool the oil

in the gearbox.

Tower

Carries the nacelle and the rotor. Generally, it is

advantageous to have a high tower, as wind

speeds increase farther away from the ground.

Anemometer and wind

vane

Measures the speed and the direction of the wind

while sending signals to the controller to start or

stop the turbine.

9

10

11

Some definitions: • Solidity: In reference to a wind energy

conversion device, the ratio of rotor blade surface area to the frontal, swept area that the rotor passes through.

• wind rose: A diagram that indicates the average percentage of time that the wind blows from different directions, on a monthly or annual basis.

• power curve: A plot of a wind energy conversion device's power output versus wind speed.

• power coefficient: The ratio of power produced by a wind energy conversion device to the power in a reference area of the free wind stream.

12

13

WIND

Wind Speed at 10 m height

SPEED

Beaufort scale

SCALE

Wind

0.0-0.4 m/s (0.0-0.9 knots) 0 Calm

0.4-1.8 m/s (0.9-3.5 knots) 1 Light

1.8-3.6 m/s (3.5-7.0 knots) 2 Light

3.6-5.8 m/s (7-11 knots) 3 Light

5.8-8.5 m/s (11-17 knots) 4 Moderate

8.5-11 m/s (17-22 knots) 5 Fresh

11-14 m/s (22-28 knots) 6 Strong

14-17 m/s (28-34 knots) 7 Strong

17-21 m/s (34-41 knots) 8 Gale

21-25 m/s (41-48 knots) 9 Gale

25-29 m/s (48-56 knots) 10 Strong Gale

29-34 m/s (56-65 knots) 11

>34 m/s (>65 knots) 12 Hurricane

Requirements: wind to electric Conversion

• Force of wind needs turbine area, height

and direction control:

• turn turbine and generator shaft,

produce electricity

• wind resources at 50meter height

• Wind translational > rotational > electric 14

How Do Wind Turbines Work?

• Today’s turbines are versatile

modular sources of electricity.

• Their blades are aerodynamically

designed to capture the maximum

energy from the wind. The wind turns

the blades, which spin a shaft

connected to a generator 15

16

The formula for calculating the

power from a wind turbine is:

17

18

Turbines today are horizontal axis upwind

machines with two or three blades, made of

a composite material like fiberglass.

The amount of power a turbine will produce

depends on the diameter. The diameter of

the rotor defines its “swept area,” or the

quantity of wind intercepted by the turbine.

The turbine’s frame is the structure onto

which the rotor, generator, and tail are

attached. The tail keeps the turbine facing

into the wind. 19

Tip Speed Ratio

The tip-speed is the ratio of the rotational

speed of the blade to the wind speed. The

larger this ratio, the faster the rotation of the

wind turbine rotor at a given wind speed.

Electricity generation requires high rotational

speeds. Lift-type wind turbines have

maximum tip-speed ratios of around 10

20

number of blades

The number of rotor blades and the total area they

cover affect wind turbine performance. For a lift-type

rotor to function effectively, the wind must flow

smoothly over the blades.

To avoid turbulence, spacing between blades should

be great enough so that one blade will not encounter

the disturbed, weaker air flow caused by the blade

which passed before it.

It is because of this requirement that most wind

turbines have only two or three blades on their rotors

21

22

Operating Characteristics

All wind machines share certain operating characteristics, such as cut-in, rated and cut-out wind speeds.

• Cut-in Speed Cut-in speed is the minimum wind speed at which the wind turbine will generate usable power. This wind speed is typically between 7 and 10 mph.

• Rated Speed The rated speed is the minimum wind speed at which the wind turbine will generate its designated rated power. For example, a "10 kilowatt" wind turbine may not generate 10 kilowatts until wind speeds reach 25 mph. Rated speed for most machines is in the range of 25 to 35 mph.

23

24

Rated Speed… At wind speeds between cut-in and rated, the

power output from a wind turbine increases as the

wind increases. The output of most machines

levels off above the rated speed.

Most manufacturers provide graphs, called "power

curves," showing how their wind turbine output

varies with wind speed.

Generators

The generator is what converts the turning

motion of a wind turbine's blades into

electricity.

Inside this component, coils of wire are rotated

in a magnetic field to produce electricity.

Different generator designs produce either

alternating current (AC) or direct current (DC),

and they are available in a large range of

output power ratings.

The generator's rating, or size, is dependent on

the length of the wind turbine's blades because

more energy is captured by longer blades. 25

It is important to select the right type of

generator to match your intended use. Most

home and office appliances operate on 120

volt (or 240 volt), 60 / 50 cycle AC. Some

appliances can operate on either AC or DC,

such as light bulbs and resistance heaters, and

many others can be adapted to run on DC.

Storage systems using batteries store DC and

usually are configured at voltages of between

12 volts and 120 volts.

26

27

Generators that produce AC are generally

equipped with features to produce the

correct voltage (120 or 240 V) and constant

frequency (60 / 50 cycles) of electricity,

even when the wind speed is fluctuating.

Transmission

The number of revolutions per minute (rpm)

of a wind turbine rotor can range between 40

rpm and 400 rpm, depending on the model

and the wind speed.

Generators typically require rpm's of 1,200 to

1,800. As a result, most wind turbines require

a gear-box transmission to increase the

rotation of the generator to the speeds

necessary for efficient electricity production.

28

Towers: Tall structures

Tower on which a wind turbine is mounted is not just a

support structure. It also raises the wind turbine so

that its blades safely clear the ground and so it can

reach the stronger winds at higher elevations.

Maximum tower height is optional in most cases,

except where zoning restrictions apply. The decision

of what height tower to use will be based on the cost

of taller towers versus the value of the increase in

energy production resulting from their use. 29

30

Studies have shown that the added cost of

increasing tower height is often justified by

the added power generated from the

stronger winds. Larger wind turbines are

usually mounted on towers ranging from 40

to 70 meters tall.