Renewable and clean energy wind turbines
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Lecture Notes. Renewable And Clean Energy Wind Turbines. Physics and Astronomy Outreach Program at the University of British Columbia. Wind Turbines. 1) How much energy is available in wind? 2) How is a useful amount of energy (or power) extracted using wind turbine technology?. Questions.

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Renewable And Clean Energy Wind Turbines

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Renewable and clean energy wind turbines

Lecture Notes

RenewableAnd CleanEnergyWind Turbines

Physics and Astronomy Outreach Program at the University of British Columbia


Questions

Wind

Turbines

1) How much energy is available in wind?

2) How is a useful amount of energy (or power) extracted using wind turbine technology?

Questions

Physics and Astronomy Outreach Program at the University of British Columbia


Background

Wind

Turbines

  • Wind energy:

  • Proposed alternative energy source

  • Is in the early stages of large scale development

  • Used in Persia as early as 500 AD to grind grain and pump water

Background

Physics and Astronomy Outreach Program at the University of British Columbia


Background1

Wind

Turbines

  • The question to ask in this early stage of large scale development:

  • Is it possible to extract a useful amount of raw energy from the wind?

  • We will consider constraints of time, location and machinery.

Background

Physics and Astronomy Outreach Program at the University of British Columbia


Time limitations

Wind

Turbines

  • Is there enough energy in wind?

  • First, it is important to make the distinction between kinetic energy and power.

  • Kinetic energy: The energy resulting from the movement of masses.

  • Power: The rate of doing useful work.

Time Limitations

Physics and Astronomy Outreach Program at the University of British Columbia


Time limitations1

Wind

Turbines

  • Wind possesses a lot of kinetic energy, but the rate at which this energy can be extracted limits the amount of useful power available.

  • How much power can be harnessed from wind?

Time Limitations

Physics and Astronomy Outreach Program at the University of British Columbia


Wind energy source

Wind

Turbines

  • Wind energy comes from a series of energy transformations from solar energy (radiation) to wind energy (kinetic).

  • About 2% of the solar energy absorbed by the earth goes into wind.

  • Solar radiation is absorbed by the surface of the earth and heats it unevenly.

Wind Energy Source

Physics and Astronomy Outreach Program at the University of British Columbia


Location limitations

Wind

Turbines

  • Uneven heating:

    • Intensity of solar energy varies due to the angle of the Sun (the equator vs. the poles).

    • Land heats up faster than water does, but also loses heat faster (inland vs. coast).

  • These differences in air temperature across the globe can create wind!

Location Limitations

Physics and Astronomy Outreach Program at the University of British Columbia


Location limitations1

Wind

Turbines

Location Limitations

Figure 1. A wind energy map of Canada showing the average power

(in W/m2) that can theoretically be extracted from the wind.

Physics and Astronomy Outreach Program at the University of British Columbia


Power available

Wind

Turbines

  • solar intensity at the top of the earth's atmosphere = 350 W/m2.

  • Given that only 2% is converted to wind thus ~ 7 W/m2 goes into wind energy.

  • 35% of wind energy (2.45 W/m2) is dissipated in the first kilometre above Earth's surface and available for turbines.

Power Available

Physics and Astronomy Outreach Program at the University of British Columbia


Power available1

Wind

Turbines

Over a period of one year, the wind energy (E) is approximately...

E = intensity ∙ Earth's SA ∙ seconds per year

= (2.45 W/m2) (5.1 x 1014 m2) (3.2x107 s)

= 4.0 x 1022 J

...which is 200 times larger than our energy consumption on Earth, estimated to be

2 x 1020 J.

Power Available

Physics and Astronomy Outreach Program at the University of British Columbia


Maximum power extracted

Wind

Turbines

  • Calculate the power extracted from wind.

  • Calculate kinetic energy, KE = ½mv2 of air passing through the rotor of the wind turbine.

  • Measure mass of air travelling through area of circle swept out by rotor blades in time Δt.

Maximum Power Extracted

Physics and Astronomy Outreach Program at the University of British Columbia


Maximum power extracted1

Wind

Turbines

Maximum Power Extracted

Figure 2. At time t = 0, the mass of air is just about to pass through the hoop, but Δt later, the mass of air has passed through the hoop. The mass of this piece of air is the product of its density ρ, area A, and length v ∙ Δt.

Physics and Astronomy Outreach Program at the University of British Columbia


Maximum power extracted2

Wind

Turbines

From this you can find the mass...

mass

ρis the density of the air (1.2 kg/m3 for standard temperature and pressure)

vis the velocity of the air

Δt is the length of time for a unit of air to pass through the loop.

A is the area swept by the blades, not the blade area.

Maximum Power Extracted

Physics and Astronomy Outreach Program at the University of British Columbia


Maximum power extracted3

Wind

Turbines

Therefore the kinetic energy, K, is found to be:

while the power of the wind passing through our hoop is:

Maximum Power Extracted

Physics and Astronomy Outreach Program at the University of British Columbia


Power extracted limitation

Wind

Turbines

  • But turbines can’t extract all of the kinetic energy of the wind.

  • Why not?

  • If this was the case the air would stop as soon as it passed through the blades and no other wind would be able to pass through.

Power Extracted Limitation

Physics and Astronomy Outreach Program at the University of British Columbia


Power extracted limitation1

Wind

Turbines

  • But you cannot capture more than 59.3% (2/3) of wind’s energy (Betz, 1919).

  • maximum ratio of P/P0 = 2/3 is found at v2/v1 ≈ 1/3.

  • Ideally you want the turbine to slow the wind down by 2/3 of its original speed.

Power Extracted Limitation

Physics and Astronomy Outreach Program at the University of British Columbia


Power extracted limitation2

Wind

Turbines

Power Extracted Limitation

Figure 3.The plot agrees with Betz’s conclusions that the maximum power output (of 59.3%) occurs when v2 is 1/3 of v1.

Physics and Astronomy Outreach Program at the University of British Columbia


Turbine power extracted

Wind

Turbines

  • Wind turbines are not 100% efficient:

  • power = efficiency ∙ max power extracted

  • where d is the diameter of the circle covered by the rotor.

Turbine Power Extracted

Physics and Astronomy Outreach Program at the University of British Columbia


Local conditions needed

Wind

Turbines

  • This expression is true for a single wind turbine in constant wind conditions.

  • In real life, however, wind conditions change.

  • What local conditions must be satisfied in order to make the use of wind turbines feasible?

Local Conditions Needed

Physics and Astronomy Outreach Program at the University of British Columbia


Local conditions needed1

Wind

Turbines

  • Wind turbines are most efficient when wind moves uniformly in the same direction.

  • Turbulence is caused by buildings, trees, and land formations.

  • The edge of a continental shelf, high ground and tundra have low turbulence and are the best locations to build a turbine.

Local Conditions Needed

Physics and Astronomy Outreach Program at the University of British Columbia


Local conditions needed2

Wind

Turbines

  • Local wind speed is also an important factor since:

  • power α (wind speed)3

  • The local wind speed should be, on average, at least 7 m/s at 25 m above the earth’s surface in order to make harnessing wind from it worthwhile.

Local Conditions Needed

Physics and Astronomy Outreach Program at the University of British Columbia


Demand and dependability

Wind

Turbines

  • Demand and dependability are important.

  • Wind is not locally predictable in the short term, and so its use should be limited to only fulfill 5 – 15% of the total energy demand of the area.

Demand and Dependability

Physics and Astronomy Outreach Program at the University of British Columbia


Demand and dependability1

Wind

Turbines

  • Setting up turbines in several locations makes wind energy more reliable.

  • The available power is averaged out.

  • Globally there is always a relatively constant amount of wind energy being harnessed at any one moment.

Demand and Dependability

Physics and Astronomy Outreach Program at the University of British Columbia


Wind turbines

Wind

Turbines

  • The machinery of a wind turbine also limits how much power can be extracted from wind.

  • Some terminology: foundation, tower, nacelle and rotor. (See Figure 4 on next slide)

Wind Turbines

Physics and Astronomy Outreach Program at the University of British Columbia


Wind turbines1

Wind

Turbines

Wind Turbines

Figure 4. A turbine is composed of a foundation, a tower,

a nacelle and a rotorconsisting of 3 blades.

Physics and Astronomy Outreach Program at the University of British Columbia


Wind turbines2

Wind

Turbines

  • The wind turns the rotor, which turns the generator to produce electricity.

  • To maximize the power extracted, the nacelle, which connects the rotor to the tower and houses the generator, can be rotated into the direction of the wind.

Wind Turbines

Physics and Astronomy Outreach Program at the University of British Columbia


Wind turbines3

Wind

Turbines

Wind Turbines

Figure 5. The dimensions and characteristics of a typical smaller

sized turbine.

Physics and Astronomy Outreach Program at the University of British Columbia


Machinery limitations

Wind

Turbines

  • The power produced by a wind turbine depends on:

    • rotor area

    • air density

    • wind speed

    • wind shear.

Machinery Limitations

Physics and Astronomy Outreach Program at the University of British Columbia


Machinery limitations1

Wind

Turbines

  • Wind shear is a difference in wind speed and direction over a short distance and is caused by mountains, coastlines and weather patterns.

  • Air density increases with colder temperatures, decreased altitude, and decreased humidity.

Machinery Limitations

Physics and Astronomy Outreach Program at the University of British Columbia


Machinery limitations2

Wind

Turbines

  • Wind speed increases the farther you get away from the ground.

  • To maximize the power output of wind turbines, rotors are tilted slightly upwards.

  • Why do you think this is?

Machinery Limitations

Physics and Astronomy Outreach Program at the University of British Columbia


Wind turbine

Wind

Turbines

Wind Turbine

Figure 6. As you get higher off the ground, the air speed increases, corresponding

to a longer arrow. The rotors are tilted slightly upwards so that each part of the

rotor is exposed to the same speed.

Physics and Astronomy Outreach Program at the University of British Columbia


Wind farms

Wind

Turbines

  • Cities and countries need huge wind farms to satisfy their energy needs.

  • To optimize energy production in a wind farm, turbines are spread 5 – 9 rotor diametres apart in the prevailing wind direction and 3 – 5 rotor diameters apart in the perpendicular direction (Fig. 7).

Wind Farms

Physics and Astronomy Outreach Program at the University of British Columbia


Wind farms1

Wind

Turbines

Figure 7. On a wind farm, turbines must be spaced out enough so that they do not

interfere with each other. As the wind passes through the turbine it slows down,

and so there is no point in putting a turbine in the region where the air is

guaranteed to be slow. One common way of spacing them out is ensuring there is

at least 5 rotor diametres between each turbine.

Wind Farms

Physics and Astronomy Outreach Program at the University of British Columbia


Wind farms2

Wind

Turbines

  • When the turbines are placed on a square grid, the power per unit land area is:

  • where n is the number of turbine diametres between turbines.

Wind Farms

Physics and Astronomy Outreach Program at the University of British Columbia


Wind farms3

Wind

Turbines

  • The average power of a wind turbine farm is the product of the capacity of the farm and the fraction of the time when the wind conditions are near optimal.

  • The capacity factor is usually around

  • 15 – 30%.

Wind Farms

Physics and Astronomy Outreach Program at the University of British Columbia


Benefits and drawbacks

Wind

Turbines

  • Now that it is established that wind is a possible source of power, the benefits and drawbacks need to be considered.

  • Why use wind power in lieu of other energy sources?

Benefits and Drawbacks

Physics and Astronomy Outreach Program at the University of British Columbia


Benefits and drawbacks1

Wind

Turbines

  • Harnessing wind power does not produce hazardous wastes, use non-renewable resources or cause significant amounts of damage to the environment.

  • Some CO2 is produced in the manufacturing of the turbines, but it is much less than the emissions from burning an energy-equivalent amount of coal or natural gas.

Benefits and Drawbacks

Physics and Astronomy Outreach Program at the University of British Columbia


Benefits and drawbacks2

Wind

Turbines

  • The use of wind power can reduce hidden costs such as those related to pollution and in the longer term, climate change.

  • Since you can farm around them, wind turbines use less space than traditional power stations.

Benefits and Drawbacks

Physics and Astronomy Outreach Program at the University of British Columbia


Benefits and drawbacks3

Wind

Turbines

  • So why, in light of these positive elements, is there so much resistance against wind turbines?

  • Arguments against include fears of damages from collapsing turbines, noise, a less attractive skyline, an unreliable power source, unnecessarily high bird fatality, and significantly modifying the Earth’s wind patterns.

Benefits and Drawbacks

Physics and Astronomy Outreach Program at the University of British Columbia


Benefits and drawbacks4

Wind

Turbines

  • DISCLAIMERS

  • Noise: the noise of a typical turbine is 45 dB at 250 m away. This level is lower than the background noise at an office or a home.

  • Reliability: the reliability of wind energy increases depending on location and how many farms are operating in a variety of sites within the area.

Benefits and Drawbacks

Physics and Astronomy Outreach Program at the University of British Columbia


Benefits and drawbacks5

Wind

Turbines

  • DISCLAIMERS

  • Birds: in the US less than 40,000 are said to die from turbine blades while hundreds of millions are said to die from domestic cats!

  • Earth’s climate: it is plausible that one would see local climate change surrounding areas with concentrated wind farms, but the large-scale climatic effects will likely be negligible.

Benefits and Drawbacks

Physics and Astronomy Outreach Program at the University of British Columbia


Benefits and drawbacks6

Wind

Turbines

  • DISCLAIMERS

  • Earth’s climate: wind turbines would be replacing coal-fired power plants, so if anything, we anticipate a considerable reduction in CO2 emissions.

Benefits and Drawbacks

Physics and Astronomy Outreach Program at the University of British Columbia


Bibliography

Wind

Turbines

Siemens Energy and Automation, Inc. Wind Turbine (online). http://www2.sea.siemens.com/NR/rdonlyres/1F91AFE0-BB27-4D13-91F7-153AEA0D6C98/0/WindTurbine.jpg [9 June 2009].

Cullum A, Kwan C, Macdonald K. British Columbia Wind Energy Feasibility Study (online). http://www.geog.ubc.ca/courses/geog376/students/class05/cskwan/intro.html [4 May 2009].

Dodge, Darrel. Part 1 - Early History Through 1875: Wind Power's Beginnings (online). Illustrated History of Wind Power Development. http://www.telosnet.com/wind/early.html [10 June 2009].

Aubrecht GJ. Solar Energy: Wind, Photovoltaics, and Large-Scale Installatons. In: Energy – Physical, Environmental, and Social Impact (3), edited by Erik Fahlgren. Upper Saddle River, NJ: Pearson Education Inc., 2006, chapt. 21, 461-465.

Kump, L.R., Kasting, J.F., and Crane, R.G. The Atmospheric Circulation System. In: The Earth System (2), edited by Patrick Lynch. Upper Saddle River, New Jersy, USA: 2004, chapt. 4, pp. 55-82.

Bibliography

Physics and Astronomy Outreach Program at the University of British Columbia


Bibliography1

Wind

Turbines

  • Environment Canada. Canadian Atlas Level 0 (online). http://collaboration.cmc.ec.gc.ca/science/rpn/modcom/eole/CanadianAtlas0.html [20 May 2009].

  • Gustavson MR. Limits to Wind Power Utilization. Science 204: 13 – 17, 1979.

  • MacKay DJC. Sustainable Energy – Without the Hot Air (Online). UIT Cambridge. http://www.inference.phy.cam.ac.uk/sustainable/book/tex/ps/253.326.pdf [4 May 2009].

  • Danish Wind Industry Association. Guided Tour on Wind Energy (online). http://www.windpower.org/en/tour.htm [4 May 2009].

  • Learning (online). Solacity Inc. http://www.solacity.com/SiteSelection.htm [20 May 2009].

  • D’Emil B, Jacobsen M, Jensen MS, Krohn S, Petersen KC, and Sandstørm, K. Wind with Miler (online). Danish Wind Industry Association. http://www.windpower.org/en/kids/index.htm [4 May 2009].

Bibliography

Physics and Astronomy Outreach Program at the University of British Columbia


Bibliography2

Wind

Turbines

  • Clarke S. Electricity Generation Using Small Wind Turbines At Your Home Or Farm (Online). Ontario Ministry of Agriculture, Foods and Rural Affairs. http://www.omafra.gov.on.ca/english/engineer/facts/03-047.htm#noise [25 May 2009].

  • Marris E and Fairless D. Wind Farms' Deadly Reputation Hard to Shift. Nature 447: 126, 2007.

  • Keith D. Wind Power and Climate Change (online). University of Calgary. http://www.ucalgary.ca/~keith/WindAndClimateNote.html [20 May 2009].

  • Accio Energy. About Accio Energy (online). http://www.hydrowindpower.com/ [12 June 2009].

Bibliography

Physics and Astronomy Outreach Program at the University of British Columbia


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