Introduction

to

Wind Energy

History

Turbine Types

Large Systems

WIND POWER - What is it?

All renewable energy (except tidal and geothermal power), ultimately comes from the sun

The earth receives 1.74 x 1017 watts of power (per hour) from the sun

About one or 2 percent of this energy is converted to wind energy (which is about 50-100 times more than the energy converted to biomass by all plants on earth)

Differential heating of the earths surface and atmosphere induces vertical and horizontal air currents that are affected by the earths

rotation and contours of the land WIND.

~ e.g.: Land Sea Breeze Cycle

Wind Zones in India

Early History

5000 BCE (before common era): Sailing ships on the Nile River were likely the first use of wind power

Hammurabi, ruler of Babylonia, used wind power for irrigation

Hero (Heron) created a wind-pumped organ

Persians created a Vertical Axis WT (VAWT) in the mid 7th Century

1191 AD: The English used wind turbines

1270: Post-mill used in Holland

1439: Corn-grinding in Holland

1600: Tower mill with rotating top or cap

1750: Dutch mill imported to America

1850: American multiblade wind pump development; 6.5 million until 1930; was produced in Heller-Allen Co., Napoleon, Ohio

1890: Danish 23-meter diameter turbine produced electricity

5Early History

6Early History

7Early History

June 19 20, 2007 Wind Energy 8

English Post Mills

Built around a central post

Wind Energy 9

Livestock Water

Later History 1920: Early Twentieth Century saw wind-driven water-pumps commonly used in

rural America, but the spread of electricity lines in 1930s (Rural Electrification Act) caused their decline

1925: Windcharger and Jacobs turbines popular for battery charging at 32V; 32Vdc appliances common for gas generators

http://telosnet.com/wind/20th.html

http://telosnet.com/wind/20th.html

1940: 1250kW Rutland Vermont (Putnam) 53m system (center)

1957-1960: 200kW Danish Gedser mill (right)

1972: NASA/NSF wind turbine research

1979: 2MW NASA/DOE 61m diameter turbine in NC

Now, many windfarms are in use worldwide

11

Grandpas Knob

Smith Putnam Machine

1941

Rutland, Vermont

1.25 MW

53 meters (largest turbine for 40 years)

Structural steel

Lost blade in 1945

12

Increased incentives

Rise in oil prices in early 1970s prompted governments research and incentives

Key players: Rocky Flats Small HAWTs < 100 kW

NASA Lewis Large HAWTs > 100 kW

Sandia Labs VAWTs

Result: the Mod series Mod 0 Plum Brook, Ohio

Mod 1 Boone, North Carolina

Mod 2 Washington, Calif, & Wyoming

13

Mod 0 (200 kW)

June 19 20, 2007 Wind Energy 14

Mod 1 (2 MW)

15

Mod 5b (3.2 MW)

Modern Wind TurbinesTurbines can be categorized into two classes

based on the orientation of the rotor.

Types of Turbines: HAWT & VAWT

HAWT (Horizontal Axis Wind Turbines) have the rotor spinning around a horizontal axis

The rotor vertical axis must turn to track the wind

Gyroscopic precession forces occur as the turbine

turns to track the wind

VAWT (Vertical Axis Wind Turbines) have the rotor

spinning around a vertical axis

This Savonius rotor will instantly extract energy regardless of the wind direction

The wind forces on the blades reverse each

half-turn causing fatigue of the mountings

Lift vs Drag VAWTs

Lift Device Darrieus Low solidity,

aerofoil blades

More efficient than drag device

Drag Device Savonius High solidity, cup

shapes are pushed by the wind

At best can capture only 15% of wind energy

VAWT Examples

Darrieus troposkein blades (jump rope)

Savonius rotor ~1925

Madaras rotor using the Magnus Effect

Rotors placed on train cars to push them around a circular track

Vortex Turbine

The SANDIA Darrieus turbinewas destroyed when left unbraked overnight

http://telosnet.com/wind/govprog.html

Some VAWT concepts

Vertical Axis Wind Turbines (VAWT)

Savonius

Darrieus

with Savonius

Panemone,

1000 B.C.

Giromill

This sample shows the diversity of VAWT over the years

VAWTs have not been commercially successful, yet

Every few years a new company comes along promising a revolutionary breakthrough in wind turbine design that is low cost, outperforms anything else on the market, and overcomes all of the previous problems with VAWTs. They can also usually be installed on a roof or in a city where wind is poor.

WindStorMag-Wind

WindTree Wind Wandler

Vertical Axis Turbines

Advantages

o Omni directional

- accepts wind from any direction

o Components can be mounted at ground level

- ease of service

- lighter weight towers

o Can theoretically use less use less materials to capture the same amount of wind

Disadvantageso Rotors generally near ground

where wind is poorer

o Centrifugal force stresses blades

o Poor self-starting capabilities

o Requires support at top of turbine rotor

o Requires entire rotor to be removed to replace bearings

o Overall poor performance and reliability

Some HAWT concepts

HAWT Examples

Charles Brush (arc light) home turbine of 1888 (center)

17 m, 1:50 step-up to drive 500 rpm generator

NASA Mod 0, 1, 2 turbines

The Mod-0A at Clayton NM produced 200kW (below left)

http://telosnet.com/wind/govprog.htmlhttp://telosnet.com/wind/20th.html

http://www.windmission.dk/

projects/Nybroe%20Home/l

Horizontal Axis Wind Turbines (HAWT)

Ref.: WTC

1.8 m

75 m

American

Farm, 1854

Sailwing,

1300 A.D.

Dutch with

fantail

Modern

Turbines

Experimental Wind farm

Dutch post

mill

Horizontal Axis Wind Turbines

Small (

Horizontal vs. Vertical-Axis

Turbine type Advantages Disadvantages

HAWT Higher wind energy conversion efficiency

Access to stronger wind due to tower height

Power regulation by stall and pitch angle control at high wind speeds

Higher installation cost, stronger tower to support heavy weight of nacelle

Longer cable from top of tower to ground

Yaw control required

VAWT Lower installation cost and easier maintenance due to ground-level gearbox and generator

Operation independent of wind direction

More suitable for rooftops where strong winds are available without tower height

Lower wind energy conversionefficiency (weaker wind on lower portion of blades & limited aerodynamic performance of blades)

Higher torque fluctuations and prone to mechanical vibrations

Limited options for power regulation at high wind speeds.

Source: B. Wu, Y. Lang, N. Zargari, and S. Kouro, Power conversion and control of wind energy systems, Wiley, 2011.30

Large Systems: Size and Numbers

Rotor hub is high above turbulent ground wind layer

Production line assembly

660kW to 7 MW power models

Groups of 10 to 1000s of turbines

Attractive, modern appearance

Large Turbine Components

060217

Ref.: www.freefoto.com/pictures/general/ windfarm/index.asp?i=2

sgroup.cms.schunk-group.com

Note railing

Airfoil Nomenclaturewind turbines use the same aerodynamic principals as aircraft

Lift & Drag Forces

The Lift Force is perpendicular to the direction of motion. We want to make this force BIG.

The Drag Force is parallel to the direction of motion. We want to make this force small.

= low

= medium

Airfoil

VR = Relative Wind

V

R r

V

= angle of attack = angle between the chord line and the direction of the relative wind, VR.

VR = wind speed seen by the airfoil vector sum of V (free stream wind) and R (tip speed).

Apparent Wind & Angle of Attack

Calculation of Wind Power

Power in the Wind

- Effect of air density ()

- Effect of swept area (A)

- Effect of wind speed (V)

AV= power of wind

Swept Area: A=R

Area of the circle swept by the rotor(m).

R

Betz Limit

Betz Limit

5926.27

16C max,p

Rotor Wake

Rotor Disc

All wind power cannot be captured by rotor or air would be completely still behind rotor and not allow more wind to pass through.

Theoretical limit of rotor efficiency is 59%

Tip-Speed Ratio

Tip-speed ratio is the ratio of the speed of the rotating blade tip to the speed of the free stream wind.

There is an optimum angle of attack which creates the highest lift to drag ratio.

Because angle of attack is dependant on wind speed, there is an optimum tip-speed ratio

RV

TSR =

R

R

Where,

= rotational speed in radians /secR = Rotor Radius

V = Wind Free Stream Velocity

R

R

Performance Over Range of Tip Speed Ratios

Power Coefficient Varies with Tip Speed Ratio

Characterized by Cp vs Tip Speed Ratio Curve

0.4

0.3

0.2

0.1

0.0

Cp

121086420

Tip Speed Ratio

Power Curve