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# Session 15 wind power

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### Session 15 wind power

1. 1. Wind Energy GE Wind Turbine, The Netherlands T. Ferguson, University of
2. 2. Wind Energy Basics • • • • • • Solar Driven Immense Resource High variability, poorly correlated to loads Non-dispatchable No economic storage of wind energy Best resources require significant high voltage transmission additions • Power proportional to cube of wind speed T. Ferguson, University of
3. 3. Wind Energy Basics P(v) A Where = ρ 3 V 2 P(v) = power, in watts A = area perpendicular to flow, in m2 ρ = density of fluid, in kg/m3 v = velocity of fluid, in m/s The ratio of power of a 10 mph wind to a 5 mph wind is substantial: (v10/v5)3 = 8 Therefore, site selection is critical. T. Ferguson, University of
4. 4. Wind Energy Basics • Wind speed increases with height as ~ 1/7 power: v2/v1 = (h2/h1)1/7 • 50 m hub elevation compared to 30 m height: about 7.6% higher speed • Height enhanced by cube of velocity: (1.076)3 = 1.245, or 24.5% more power • Above about 1 km above earth’s surface, wind not appreciably affected by surface T. Ferguson, University of
5. 5. Wind Energy Basics • ρair = 1.226 kg/m3 at 15 °C (288°K) and 1 atmosphere (29.92 inHg) • Using PV = nRT (ideal gas law): – ρ variation with Temperature extremes: • 90°F = 32° = 305 °K: V305/V288 = 305/288 = 1.059 Therefore, ρ305 = 1/1.059 X ρ288 = 0.944 ρ288 Hot air (w.r.t. 15 °C) reduces available power by ~ 6% • -40°F = 233°K: ρ233 = 1.236 ρ288 Cold air (w.r.t. 15 °C) increases available power by ~ 24% • Therefore, wind power is relatively sensitive to air temp T. Ferguson, University of
6. 6. Wind Energy Basics • ρair = 1.226 kg/m3 at 15 °C (288°K) and 1 atmosphere (29.92 inHg, or 760 mmHg) • Using PV = nRT (ideal gas law): – ρ variation with pressure extremes: • 30.15 in. = 0.8% increase in ρ (w.r.t. 29.92 in.) • 29.00 in. = 3.1% decrease in ρ • So, cold air consistent with high pressure systems are advantageous T. Ferguson, University of
7. 7. Wind Energy Systems Now, place a wind turbine in the air flow: • Maximum attainable wind power coefficient = Betz ratio = ηmax = 0.593 • Modern units capable of ~ 50% (40% after gearbox and electrical losses) T. Ferguson, University of
8. 8. Wind Energy Systems Two or Three Blades: (Lift vs. drag design) 1. Electrical generation requires higher rotational speeds possible with lift design 2. Lift design must avoid turbulence; hence, two or three blades 3. Pocket of low pressure on downwind side 4. Pocket pulls blade toward it – lift 5. Direct force on blade pushes blade – drag 6. Force of lift is about 10 times that of drag 7. Both forces cause rotor to spin 8. Rotor typically at 40-400 rpm 9. AC generator requires 1200-1800 rpm 10. Hence, gearbox required T. Ferguson, University of
9. 9. Wind Energy Systems Angle of attack near tip Wind Nacelle Angle of attack near Near hub Hub end of blade 1. Blade more prone to stall near hub 2. Twist is self protecting in high winds 3. Blades usually glass fiber-reinforced plastic (steel and Al are heavy and prone to metal fatigue) 4. Yaw control keeps perpendicular to wind flow 5. Cable twist counter “yaws” the unit occasionally to unravel cables T. Ferguson, University of Photo from GE website; 2.5 MW Series Turbines
10. 10. Wind Energy Systems • Cut-in: Wind speed at which usable power produced • Rated: Minimum speed to produce rated power • Cut-out: Wind speed at which unit brakes • If interconnected to grid at speeds below cut-in, unit would run as motor • Once cut-in reached, generator needs load attached to avoid overspeeding • Units typically produce 660 v at 60 Hz; transformer at each tower steps up to 10-35 kV T. Ferguson, University of
11. 11. Wind Energy Systems Note that, even though wind speed (and available power) increases after 12 m/s, the turbine output remains flat T. Ferguson, University of 4 m/s = 9 mph 13 m/s = 29 mph 25 m/s = 55 mph Source: GE website for 2.5 MW series wind turbines; GE claims to have manufactured over 5000 megawatt-plus turbines
12. 12. Wind Energy Systems T. Ferguson, University of Source: GE website for 2.5 MW series wind turbine
13. 13. Wind Energy Systems • Adjacent turbines interfere to reduce energy • Rules of thumb: – Space towers at least 3 rotor diameters to get out of windshade – Usually 3 to 5 diameters perpendicular to prevailing winds – Usually 5 to 9 diameters in prevailing wind direction – Mitigates the greater turbulence T. Ferguson, University of
14. 14. Wind Energy Systems A rough approximation of unit performance within a farm: x X X Efficiency of Nth row = y Prevailing Winds F≈ X Turbine/tower location T. Ferguson, University of X Row 1 X X Row 2 -2N e R2 Where R = x/D D = rotor diameter For D = 100 m and x = 1000 m, R = 10. Efficiency of second row is F ≈ e(-4/100) = 96% Efficiency of tenth row is F ≈ e(-20/100) = 82%
15. 15. Wind Energy Systems “The fewer rows deep, the better” T. Ferguson, University of
16. 16. Minnesota Wind Integration Study • May, 2005: Legislature requires study of impacts • The objectives of the study are to: 1. Evaluate the impacts on reliability and costs associated with increasing wind capacity to 15%, 20%, and 25% of Minnesota retail electric energy sales by 2020; 2. Identify and develop options to manage the impacts of the wind resources; 3. Build upon prior wind integration studies and related technical work; 4. Coordinate with recent and current regional power system study work; 5. Produce meaningful, broadly supported results through a technically rigorous, inclusive study process. T. Ferguson, University of
17. 17. Minnesota Wind Integration Study • The work reported here addresses two major questions: 1. To what extent would wind generation contribute to the electric supply capacity needs for Minnesota electric utility companies? 2. What are the costs associated with scheduling and operating conventional generating resources to accommodate the variability and uncertainty of wind generation? T. Ferguson, University of
18. 18. Meteorology • Affects wind generation output across wide areas • Also affects electrical demand • High winds during peak demand would be ideal – integration costs would be low • However, correlation is far from perfect T. Ferguson, University of
19. 19. Meteorology • Historical weather data from NWS used • Wind penetration levels of 15, 20 and 25% of projected 2020 retail electric loads • Output at 152 grid points, at 40 MW each, calculated every 5 minutes • A 20% energy penetration in 2020 will require 5000 MW of wind nameplate T. Ferguson, University of
20. 20. Turbine Power Curve T. Ferguson, University of Source: Final Report – 2006 Minnesota Wind Integration Study – Volume 1 – November 30, 2006 (MN PUC)
21. 21. Operating Reliability Constraints • • • • • Objective: very high reliability; lowest cost Continuously match generation to load Voltage at all nodes within limits Regulate frequency, maintain synchronism System capable of withstanding major outages or loss of major elements T. Ferguson, University of
22. 22. Integration Study Conclusions • Increases costs to load ranging from \$2.11 (15% penetration) to \$4.41/MWh (25%) • Combining balancing areas significantly improves financial results • Wider geographic area = more stable output • Effective load carrying capability (ELCC) ranged from 5% to 20% of nameplate • Ferguson, Extensive transmission upgrades needed T. University of
23. 23. Mean Wind Speed @ 80m AGL T. Ferguson, University of Source: Final Report – 2006 Minnesota Wind Integration Study – Volume 1 – November 30, 2006 (MN PUC)
24. 24. Wind Net Capacity Factor T. Ferguson, University of Source: Final Report – 2006 Minnesota Wind Integration Study – Volume 1 – November 30, 2006 (MN PUC)
25. 25. Seasonal Output T. Ferguson, University of Source: Final Report – 2006 Minnesota Wind Integration Study – Volume 1 – November 30, 2006 (MN PUC)
26. 26. Seasonal Output T. Ferguson, University of Source: Final Report – 2006 Minnesota Wind Integration Study – Volume 1 – November 30, 2006 (MN PUC)
27. 27. Impact on Large Coal Units T. Ferguson, University of Source: Final Report – 2006 Minnesota Wind Integration Study – Volume 1 – November 30, 2006 (MN PUC)
28. 28. Environmental Benefits T. Ferguson, University of Source: Final Report – 2006 Minnesota Wind Integration Study – Volume 1 – November 30, 2006 (MN PUC)