1. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Lecture Notes

2. 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? Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia

3. 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 Wind Turbines

4. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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. Wind Turbines

5. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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. Wind Turbines

6. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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? Wind Turbines

7. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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 Turbines

8. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Uneven heating: o Intensity of solar energy varies due to the angle of the Sun (the equator vs. the poles). o 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! Wind Turbines

9. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Figure 1. A wind energy map of Canada showing the average power (in W/m 2 ) that can theoretically be extracted from the wind. Wind Turbines

10. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia solar intensity at the top of the earth's atmosphere = 350 W/m 2. Given that only 2% is converted to wind thus ~ 7 W/m 2 goes into wind energy. 35% of wind energy (2.45 W/m 2 ) is dissipated in the first kilometre above Earth's surface and available for turbines. Wind Turbines

11. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Over a period of one year, the wind energy (E) is approximately... E = intensity ∙ Earth's SA ∙ seconds per year = (2.45 W/m 2 ) (5.1 x 10 14 m 2 ) (3.2x10 7 s) = 4.0 x 10 22 J...which is 200 times larger than our energy consumption on Earth, estimated to be 2 x 10 20 J. Wind Turbines

12. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Calculate the power extracted from wind. Calculate kinetic energy, KE = ½mv 2 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. Wind Turbines

13. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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. Wind Turbines

14. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia From this you can find the mass... mass ρ is the density of the air (1.2 kg/m 3 for standard temperature and pressure) v is 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. Wind Turbines

15. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Therefore the kinetic energy, K, is found to be: while the power of the wind passing through our hoop is: Wind Turbines

16. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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. Wind Turbines

17. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia But you cannot capture more than 59.3% (2/3) of wind’s energy (Betz, 1919). maximum ratio of P/P 0 = 2/3 is found at v 2 /v 1 ≈ 1/3. Ideally you want the turbine to slow the wind down by 2/3 of its original speed. Wind Turbines

18. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Figure 3.The plot agrees with Betz’s conclusions that the maximum power output (of 59.3%) occurs when v 2 is 1/3 of v 1. Wind Turbines

19. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Wind turbines are not 100% efficient: power = efficiency ∙ max power extracted where d is the diameter of the circle covered by the rotor. Wind Turbines

20. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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? Wind Turbines

21. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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. Wind Turbines

22. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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. Wind Turbines

23. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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. Wind Turbines

24. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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. Wind Turbines

25. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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

26. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Figure 4. A turbine is composed of a foundation, a tower, a nacelle and a rotorconsisting of 3 blades. Wind Turbines

27. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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

28. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Figure 5. The dimensions and characteristics of a typical smaller sized turbine. Wind Turbines

29. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia The power produced by a wind turbine depends on: rotor area air density wind speed wind shear. Wind Turbines

30. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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. Wind Turbines

31. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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? Wind Turbines

32. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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. Wind Turbines

33. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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 Turbines

34. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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 Turbines

35. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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 Turbines

36. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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 Turbines

37. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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? Wind Turbines

38. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Harnessing wind power does not produce hazardous wastes, use non-renewable resources or cause significant amounts of damage to the environment. Some CO 2 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. Wind Turbines

39. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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. Wind Turbines

40. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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. Wind Turbines

41. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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. Wind Turbines

42. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 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. Wind Turbines

43. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia DISCLAIMERS Earth’s climate: wind turbines would be replacing coal-fired power plants, so if anything, we anticipate a considerable reduction in CO 2 emissions. Wind Turbines

44. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 1. 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]. http://www2.sea.siemens.com/NR/rdonlyres/1F91AFE0-BB27-4D13- 91F7-153AEA0D6C98/0/WindTurbine.jpg 2. Cullum A, Kwan C, Macdonald K. British Columbia Wind Energy Feasibility Study (online). http://www.geog.ubc.ca/courses/geog376/students/class05/cskwan/int ro.html [4 May 2009]. http://www.geog.ubc.ca/courses/geog376/students/class05/cskwan/int ro.html 3. 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]. http://www.telosnet.com/wind/early.html 4. 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. 5. 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. Wind Turbines

45. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 6. Environment Canada. Canadian Atlas Level 0 (online). http://collaboration.cmc.ec.gc.ca/science/rpn/modcom/eole/Canadian Atlas0.html [20 May 2009]. http://collaboration.cmc.ec.gc.ca/science/rpn/modcom/eole/Canadian Atlas0.html 7. Gustavson MR. Limits to Wind Power Utilization. Science 204: 13 – 17, 1979. 8. MacKay DJC. Sustainable Energy – Without the Hot Air (Online). UIT Cambridge. http://www.inference.phy.cam.ac.uk/sustainable/book/tex/ps/253.326.p df [4 May 2009]. http://www.inference.phy.cam.ac.uk/sustainable/book/tex/ps/253.326.p df 9. Danish Wind Industry Association. Guided Tour on Wind Energy (online). http://www.windpower.org/en/tour.htm [4 May 2009].http://www.windpower.org/en/tour.htm 10. Learning (online). Solacity Inc. http://www.solacity.com/SiteSelection.htm [20 May 2009]. http://www.solacity.com/SiteSelection.htm 11. 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].http://www.windpower.org/en/kids/index.htm Wind Turbines

46. Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia 12. 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].http://www.omafra.gov.on.ca/english/engineer/facts/03- 047.htm#noise 13. Marris E and Fairless D. Wind Farms' Deadly Reputation Hard to Shift. Nature 447: 126, 2007. 14. Keith D. Wind Power and Climate Change (online). University of Calgary. http://www.ucalgary.ca/~keith/WindAndClimateNote.html [20 May 2009].http://www.ucalgary.ca/~keith/WindAndClimateNote.html 15. Accio Energy. About Accio Energy (online). http://www.hydrowindpower.com/ [12 June 2009]. http://www.hydrowindpower.com/ Wind Turbines