wind power turbine design

8/8/2019 Wind Power Turbine Design

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Ken Youssefi Engineering 10, SJSU 1

Wind Power and WindTurbines

ENGR 10

San Jose State University
http://en.wikipedia.org/wiki/Image:Mod-0_Wind_turbine.jpg


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Alternative Sources of Energy


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Wind Turbine Energy


4/35Ken Youssefi Engineering 10, SJSU 4

Wind Turbine

Wind energy is created when the atmosphere is heated unevenly bythe Sun, some patches of air become warmer than others. Thesewarm patches of air rise, other air rushes in to replace them thus,

wind blows.

A wind turbine extracts energy from moving air by slowing the wind

down, and transferring this energy into a spinning shaft, whichusually turns a generator to produce electricity. The power in thewind thats available for harvest depends on both the wind speedand the area thats swept by the turbine blades.



Two types of turbine design are possible Horizontal axis and Vertical axis.In horizontal axis turbine, it is possible to catch more wind and so the poweroutput can be higher than that of vertical axis. But in horizontal axis design,the tower is higher and more blade design parameters have to be defined. Invertical axis turbine, no yaw system is required and there is no cyclic load on

the blade, thus it is easier to design. Maintenance is easier in vertical axisturbine whereas horizontal axis turbine offers better performance.

Wind Turbine Design

Horizontal axisTurbine

Vertical axisTurbine



Main components of a Wind Turbine

RotorThe portion of the wind turbine that collects energy from the wind is called therotor. The rotor usually consists of two or more wooden, fiberglass or metalblades which rotate about an axis (horizontal or vertical) at a rate determined

by the wind speed and the shape of the blades. The blades are attached tothe hub, which in turn is attached to the main shaft.

Rotor


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What should be the angle of attach?

What should be the blade profile?

Conduct an internet search to obtain enoughinformation to help you decide on the number and

profile of the blades.

How many blades to use?

Blade Length

Blade NumberBlade Pitch

Blade Shape

Blade MaterialsBlade Weight

Rotor Blade Variables


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Wind Turbine

For the drag design, the wind literally

pushes the blades out of the way.Drag powered wind turbines arecharacterized by slower rotationalspeeds and high torque capabilities.They are useful for the pumping,

sawing or grinding work that Dutch,farm and similar "work-horse"windmills perform. For example, afarm-type windmill must develop high

torque at start-up in order to pump, orlift, water from a deep well.

Drag Design

Blade designs operate on either the principle of drag or lift.


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Wind Turbine

The lift blade design employs the same principle that enables airplanes, kites andbirds to fly. The blade is essentially an airfoil, or wing. When air flows past the blade,a wind speed and pressure differential is created between the upper and lower bladesurfaces. The pressure at the lower surface is greater and thus acts to "lift" the

blade. When blades are attached to a central axis, like a wind turbine rotor, the lift istranslated into rotational motion. Lift-powered wind turbines have much higherrotational speeds than drag types and therefore are well suited for electricitygeneration.

Lift Design


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The angle between the chord line of the airfoil and the flight direction iscalled the angle of attack. Angle of attack has a large effect on the liftgenerated by an airfoil. This is the propeller efficiency. Typically, numbershere can range from 1.0 to 15.0 degrees.

Angle of attack (blade angle)

Wind Turbine Blade Design


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What causes wind?

A. Air pressure

B. Weight of the atmosphere

C. Pressure difference

D. Low pressureE. High pressure

Review Question 1


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Review Question 2

What are the units of pressure?

A. Force/Area

B. Pascals (Pa)

C. Pounds per square inch (psi)D. Millirads

E. B and C


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The determination of the number of blades involvesdesign considerations of aerodynamic efficiency,component costs, system reliability, and aesthetics.

Noise level is not affected significantly by the bladecount. Aerodynamic efficiency increases with thenumber of blades but with diminishing return.

Increasing the number of blades from one to two yields asix percent increase in aerodynamic efficiency, whereas

increasing the blade count from two to three yields onlyan additional three percent in efficiency. Furtherincreasing the blade count yields minimal improvementsin aerodynamic efficiency and sacrifices too much in

blade stiffness as the blades become thinner.Generally, the fewer the number of blades, the lower thematerial and manufacturing costs will be. Higherrotational speed reduces the torques in the drive train,resulting in lower gearbox and generator costs.


One blade rotor

Blade Number


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A rotor with an even number of blades will cause stabilityproblems for a wind turbine. The reason is that at the verymoment when the uppermost blade bends backwards,because it gets the maximum power from the wind, the

lowermost blade passes into the wind shade in front ofthe tower. This produces uneven forces on the rotor shaftand rotor blade.

Even or Odd Number of Blades


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Wind Turbine Blade Design (Shape)

To study how the wind moves relative to the rotorblades of a wind turbine, attach red ribbons to thetip of the rotor blades and yellow ribbons about 1/4of the way out from the hub.

Since most wind turbines have constant rotationalspeed, the speed with which the tip of the rotor blademoves through the air (the tip speed) is typicallysome 64 m/s, while at the centre of the hub it is zero.

1/4 out from the hub, the speed will then be some 16m/s.

The yellow ribbons close to the hub of the rotor will

be blown more towards the back of the turbine thanthe red ribbons at the tips of the blades. This isbecause, at the tip of the blades, the speed is some8 times higher than the speed of the wind hitting thefront of the turbine.


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Wind Turbine Blade Design (Shape)

Rotor blades for wind turbines are always twisted. Seen from therotor blade, the wind will be coming from a much steeper angle

(more from the general wind direction in the landscape), as youmove towards the root of the blade, and the centre of the rotor. Arotor blade will stop giving lift (stall), if the blade is hit at an angle ofattack which is too steep.

Therefore, the rotor blade has to be twisted, so as to achieve anoptimal angle of attack throughout the length of the blade.


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P G t d b Wi d T bi


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Power Generated by Wind Turbine

Swept area

Diameter

Elevation

There are about 4,800 wind turbines in California at Altamont Pass(between Tracy and Livermore). The capacity is 580 MW, enough toserve 180,000 homes. In 2003, Altamont generated 822x106 kW hours,enough to provide power for 126,000 homes (6500 Kw-hr per house)


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Power = ()(A)(V)3

A = swept area = (radius)2, m2

V = Wind Velocity, m/sec.

= 1.16 kg/m3, at 1000 feet elevation

= 1.00 kg/m3, at 5000 feet elevation

= 1.203 kg/m3 at San Jose, at 85 feet elevation. The averagewind velocity is 5 mph at 50m tower height

= Density of air = 1.2 kg/m3 (.0745 lb/ft3), at sea level, 20 oC and dry air

= 1.16 kg/m3 at Altamont pass, at 1010 feet elevation and average windvelocity of 7m/s at 50m tower height (turbines need a minimum of 14mph,6.25 m/s, wind velocity to generate power).

A


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The tip-speed ratio is the ratio of the rotational speed of the blade tothe wind speed. The larger this ratio, the faster the rotation of the windturbine rotor at a given wind speed. Electricity generation requires

high rotational speeds. Lift-type wind turbines have maximum tip-speed ratios of around 10, while drag-type ratios are approximately 1.Given the high rotational speed requirements of electrical generators,it is clear that the lift-type wind turbine is the most practical forthis application.

The number of blades that make up a rotor and the total area theycover affect wind turbine performance. For a lift-type rotor to functioneffectively, the wind must flow smoothly over the blades. To avoid

turbulence, spacing between blades should be great enough so thatone blade will not encounter the disturbed, weaker air flow caused bythe blade which passed before it.

Tip Speed Ratio

Wind Turbine

Wind Turbine


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The generator converts the mechanical energy of the turbine to electricalenergy (electricity). Inside this component, coils of wire are rotated in a

magnetic field to produce electricity. Different generator designs produceeither alternating current (AC) or direct current (DC), available in a large rangeof output power ratings.Most home and office appliances operate on 120 volt (or 240 volt), 60 cycleAC. 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. Storagesystems using batteries store DC and usually are configured at voltages ofbetween 12 volts and 120 volts.Generators that produce AC are generally equipped with features to produce

the correct voltage (120 or 240 V) and constant frequency (60 cycles) ofelectricity, even when the wind speed is fluctuating.

Generators

Wind Turbine


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Wind Turbine

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 thewind speed. Generators typically require rpm's of 1,200 to 1,800. As aresult, most wind turbines require a gear-box transmission to increasethe rotation of the generator to the speeds necessary for efficientelectricity production. Some DC-type wind turbines do not usetransmissions. Instead, they have a direct link between the rotor andgenerator. These are known as direct drive systems. Without atransmission, wind turbine complexity and maintenance requirementsare reduced, but a much larger generator is required to deliver the

same power output as the AC-type wind turbines.

Transmission


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Cut-in speed is the minimum wind speed at which the wind turbine willgenerate usable power. This wind speed is typically between 7 and 15 mph.

Wind Turbine

Cut-in Speed

Rated SpeedThe rated speed is the minimum wind speed at which the wind turbinewill 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. Atwind speeds between cut-in and rated, the power output from a windturbine increases as the wind increases. The output of most machineslevels off above the rated speed. Most manufacturers provide graphs,called "power curves," showing how their wind turbine output varies withwind speed.


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Wind Turbine

At very high wind speeds, typically between 45 and 80 mph, most windturbines cease power generation and shut down. The wind speed atwhich shut down occurs is called the cut-out speed. Having a cut-outspeed is a safety feature which protects the wind turbine from damage.Shut down may occur in one of several ways. In some machines anautomatic brake is activated by a wind speed sensor. Some machinestwist or "pitch" the blades to spill the wind. Still others use "spoilers,"

drag flaps mounted on the blades or the hub which are automaticallyactivated by high rotor rpm's, or mechanically activated by a springloaded device which turns the machine sideways to the wind stream.Normal wind turbine operation usually resumes when the wind drops

back to a safe level.

Cut-out Speed

Wind Turbine


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Wind Turbine

It is the flow of air over the blades and through the rotor area that makes awind turbine function. The wind turbine extracts energy by slowing thewind down. The theoretical maximum amount of energy in the wind thatcan be collected by a wind turbine's rotor is approximately 59.3%. Thisvalue is known as the Betz limit. If the blades were 100% efficient, a windturbine would not work because the air, having given up all its energy,would entirely stop. In practice, the collection efficiency of a rotor is not as

high as 59%. A more typical efficiency is 35% to 45%. A complete windenergy system, including rotor, transmission, generator, storage and otherdevices, which all have less than perfect efficiencies, will deliver between10% and 30% of the original energy available in the wind.

Betz Limit


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California generates 11% of all commercial wind power generationin the world, Europe generates 70%.

There are about 4,800 wind turbines in California at Altamont Pass(between Tracy and Livermore). The capacity is 580 MW, enough toserve 180,000 homes. In 2003, Altamont generated 822x106 kW

hours, enough to provide power for 126,000 homes.

In 2003, the California wind industry reported 3.7x109 kW hourof electricity output, enough to provide electricity for 570,000homes (twice the size of San Jose). Average household uses6,500 kW hour of electricity annually.

PG&E reported, in 2006, out of all energy delivered, 12% was fromrenewable energy sources; 11% of this was from wind power.



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Wind turbines with rotors (turbine blades and hub) that are about 8 feet in

diameter (50 square feet of swept area) may peak at about 1,000 watts (1kilowatt; kW), and generate about 75 kilowatt-hours (kWh) per month with a 10mph average wind speed. Turbines smaller than this may be appropriate forsailboats, cabins, or other applications that require only a small amount of

electricity. [Small Wind]

For wind turbine farms, its reasonable to use turbines with rotors up to 56 feet

in diameter (2,500 square feet of swept area). These turbines may peak atabout 90,000 watts (90 kW), and generate 3,000 to 5,000 kWh per month at a10 mph average wind speed, enough to supply 200 homes with electricity.

Homes typically use 500-1,500 kilowatt-hours of electricity per month.Depending upon the average wind speed in the area this will require a windturbine rated in the range 5-15 kilowatts, which translates into a rotor diameterof 14 to 26 feet.

Example Residential Wind Turbine


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Bergey wind turbines operate at variable speedto optimize performance and reduce structuralloads. Power is generated in a direct drive, lowspeed, permanent magnet alternator. Theoutput is a 3-phase power that varies in bothvoltage and frequency with wind speed. This

variable power (wild AC) is not compatible withthe utility grid. To make it compatible, the windpower is converted into grid-quality 240 VAC,single phase, 60 hertz power in an IGBT-typesynchronous inverter, the GridTek Power

Processor. The output from the GridTek can bedirectly connected to the home or businesscircuit breaker panel. Operation of the system isfully automatic. It has a rotor diameter of 23 feetand is typically installed on 80 or 100 foot

towers.

10kW Turbine $27,900

100 ft.Tower Kit $9,200

Tower Wiring Kit $1,000Total Cost: $38,100

Example Residential Wind Turbine

Wind Turbine


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Doubling the tower height increases the expected wind speeds by 10%and the expected power by 34%. Doubling the tower height generallyrequires doubling the diameter as well, increasing the amount of materialby a factor of eight.

At night time, or when the atmosphere becomes stable, wind speedclose to the ground usually subsides whereas at turbine altitude, it doesnot decrease that much or may even increase. As a result, the wind

speed is higher and a turbine will produce more power than expected -doubling the altitude may increase wind speed by 20% to 60%.

Wind Turbine

Tower heights approximately two to three times theblade length have been found to balance material costsof the tower against better utilization of the moreexpensive active components.

Wind Energy Generation


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Wind Energy Generation

CALIFORNIA ELECTRICAL ENERGY GENERATION, 1997 TO 2005

TOTAL PRODUCTION, BY RESOURCE TYPE

(Gigawatt Hours)

1997 1998 1999 2000 2001 2002 2003 2004 2005

Total Generation 255,080 276,412 275,803 280,496 265,059 272,509 276,969 289,359 287,977

Hydroelectric 41,400 48,757 41,627 42,053 25,005 31,221 36,140 34,372 39,891

Nuclear 37,267 41,715 40,419 43,533 33,294 34,353 35,594 30,241 36,155

Coal 27,114 34,537 36,327 36,804 27,636 27,817 27,294 28,589 28,129

Oil 143 123 55 449 1,328 481 107 119 148

Gas 74,341 82,052 84,703 106,878 113,145 90,991 91,994 104,612 96,047

Geothermal 11,950 12,554 13,251 13,456 13,619 13,867 13,771 14,000 14,380

Organic Waste 5,701 5,266 5,663 6,086 6,185 6,261 5,935 5,903 6,027

Wind 2,739 2,776 3,433 3,604 3,242 3,546 3,316 4,258 4,084

Solar 810 839 838 860 837 851 759 741 660

Other 896 230 0 0 0 261 249 246 0

Energy Imports 52,720 47,563 49,487 26,774 40,768 62,859 61,811 66,278 62,456 (1)

1.4%

.25%


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Energy Cost

Cost of Electricity Generation1994 Compared to 2003

Technology [1]1994 Cost of Electricity

(cents/kWh)Current Cost of Electricity

(2003 data, cents/kWh)

Hydroelectric [2] 0.31 to 4.4 0.25 to 2.7

Nuclear [3] 2.5 1.4 to 1.9

Coal [4] 1.9 to 2.3 1.8 to 2.0

Natural Gas [5] 2.5 to 11.7 5.2 to 15.9

Solar [6] 16.4 to 30.5 13.5 to 42.7

Wind [7] 7.6 4.6


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Northern California annual average wind power


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g p

10 m (33 ft) 50 m (164 ft)

Speed(b) m/s (mph) Speed(b) m/s (mph)

0 0

4.4 (9.8) 5.6 (12.5)2

5.1 (11.5) 6.4 (14.3)3

5.6 (12.5) 7.0 (15.7)4

6.0 (13.4) 7.5 (16.8)5

6.4 (14.3) 8.0 (17.9)6

7.0 (15.7) 8.8 (19.7)7

9.4 (21.1) 11.9 (26.6)

1

WindPowerClass*

Bay Area

Wind Speed


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Wind SpeedBuilding wind facilities in the corridor that stretches from the Texas panhandle to

North Dakota could produce 20% of the electricity for the United States at a costof $1 trillion. It would take another $200 billion to build the capacity to transmitthat energy to cities and towns.

In 2007, the U.S. Gross

Domestic Product (GDP,goods and services) wasroughly 13.7 trillion andspending budget was 2.7

wind power turbine design

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