Wind Energy Introduction

Energy and Environment (MECH 433):

Wind Energy (Introduction)

Ming Li

School of Engineering

The University of Liverpool

Introduction

Aims and objectives: To give students an understanding of the advantages and

disadvantages of wind energy generation methods;

To develop detailed knowledge of wind energy capture;

To develop skills in quantitative analysis of wind energy generation methods.

Learning outcomes: Impact of wind energy generation methods on the environment

Quantitative analysis techniques for energy generation methods

Applying analytical methods to wind power generation problems

Decision making in complex and unpredictable situations

05/03/2015 Sustainable Civil Engineering Group Design (CIVE488) 2

Syllabus

0-2hr: Wind and wind energy (Power)

0-2hr: Basics of wind turbines

2-3hr: Aerodynamics & component design

3-5hr: Power and energy from wind turbines

3-5hr: Environment impacts

5-6hr: Economics and future


Assessment

CA: 1 Q&A 5% Thursday 12th March, due Friday 2wks after.

Exam: 1 question 20%

Main references: Boyle, G. (2012) Renewable Energy, Power for a sustainable future, 3rd ed.

Oxford University Press.


The wind

All our energy comes from the Sun in the form of light.

Because of the Earths spinning axis is tilted at an angle to its orbiting plane, it receives different

amounts of sunshine at different time of the year.

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Energy and Environment (MECH433)

The wind

The differential solar heating of the Earths surface causes variations in atmosphere pressure, and leads

to the movement of air masses as the principle of the

Earths wind systems.

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The wind


Warm air rises and cool

air descends.

Wind is influenced by

the terrain and shapes

the terrain in turn.

Air flow is driven from

high pressure area to

the low pressure area.

05/03/2015 Energy and Environment (MECH433)

The wind

Wind is very unpredictable in magnitude and direction;

Wind shear: increase of wind speed with height;

Wind speed and direction affected by heat (sunshine);

Terrain friction causes Turbulence;

Extreme wind (gust) can cause damage and even disasters.

8

Wind energy

Wind mills has been used for thousands of years for milling grain, pumping water and other

applications.

Wind turbines are used as a pollution-free means of generating electricity on a significant scale.


Wind energy

The total amount of economically extractable power available from the wind is considerably more than present human power use from all sources.

Advantages: Free and renewable Has been used over many centuries (proven technology)

Disadvantages: Intermittent and unsteady in direction and speed Very low energy density and use of large surface Noise and vibration from wind turbines Visual intrusion of wind turbines Initial construction and subsequent maintenance cost


Wind energy


Area A Kinetic energy = 2

02

1mV

0AVm

Kinetic energy = 3

02

1AV

(in joules per sec.)

3

05.0 AVP

: air density A : swept rotor area

V0 : (free stream) wind speed

Total power:

Wind energy

Example: wind at 10 m/s through a circular area of 1 m in radius

However, not all the power available in the wind can be extracted. So the true power that

can be extracted is a fraction of the above:


Cp: power coefficient

WAVP 188410114.32.15.05.0 323

0

3

02

1AVCP p

Wind energy

Normally 5 m/s wind is required to turn a wind turbine.

An average wind speed of 6 m/s to turn wind into electricity.

On-shore:

Easy to access for construction and maintenance

Easy to connect to the Grid

Wind quality may not be high

Land use

Environmental issues

Offshore:

Large area and stronger wind

Shipping

Corrosive environment

Maintenance cost


Wind energy

Price of Electricity 4 ~ 12p per unit (1 kW hour), depending on suppliers

and fuel market.

Unit price of electricity is largely influenced by gas price (40%).

Onshore wind power at around 3.2p.

Small-scale wind turbines at 12p.

Domestic customers pay 24p per unit up to 900 units and 12p per unit above (depending on suppliers)


Wind energy


Wind turbines

Earliest design of wind turbine is by James Blyth of Strathclyde University in 1887, built at Marykirk

(Scotland).

Since 1980s, wind power technology have become one of fastest growing Renewable

Energy technology worldwide, with 194GW

capacity built by 2010.

To understand the mechanism and system, multidiscipline knowledge is required:

meteorology, aerodynamic, electrical, structural,

civil and mechanical engineering.


Wind turbines


Wind turbines

Horizontal Axis (HAWT)

industrial standard design of 3-bladed and 2-bladed turbines

On-shore

Off-shore


Wind turbines

Solidity is used to describe the fraction of the swept area that is solid (blade).

Multi-blade turbines have high-solidity rotors

Modern electricity generating wind turbine have low solidity rotors.

Speed of rotation:

Revolution per minute (RPM)

Angular velocity (radians per second)


11 10472.060

21 radsredsrpm

Wind turbines

Tip speed U: tangential velocity of the rotor at the tip of the blades (m/s)

Tip speed ratio : ratio between tip speed U and upstream wind velocity V0


0V

U

Wind turbines

To extract energy efficiently, the blades need to interact with wind as much as possible through the rotors swept area.

High-solidity multi-blade wind turbines interact with all wind at very low tip speed ratio.

Low-solidity turbine have to travel fast to virtually fill up the swept area to interact with wind passing through.

Optimum tip speed ratios for modern low-solidity turbines range between 6-20.

However, large number of blades can interfere with air flow and cause much stronger turbulence, hence reduce

the efficiency of the turbine.


Wind turbines

Vertical Axis (VAWT)

various designs and creative


Wind turbines

Vertical Axis (VAWT)

At present, the VAWTs are not economically competitive with HAWTs.

However, they offers significant advantages over HAWTS in blades loading and fatigue.

They are not subjects to the major gravitational cyclic loadings that the large diameter HAWTs

experience.

They often can be operated with high reliability.


Wind turbines


Lillgrund Wind Farm, Sweden

Foote Creek Wind Farm, U.S.

Wind Energy Introduction

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