013_20160726_Wind energy
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This document provides an overview of wind energy and wind turbines. It discusses the advantages of wind energy such as being clean and having an abundant domestic source. It also discusses disadvantages like intermittency and land use impacts. The document describes different types of wind turbines including horizontal and vertical axis designs. It provides information on wind resources and wind power potential in the United States. Key concepts in wind turbine operation and aerodynamics are explained like Betz's law. Cost trends for wind power and the future outlook of the industry are also summarized.
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013_20160726_Wind energy
- 1. ENME701: Wind Energy Reinhard Radermacher 2016
- 3. Certainty of Wind Resource in the US http://rredc.nrel.gov/wind/pubs/atlas/maps/chap2/2-07m.html
- 4. Advantages of Wind Energy • Clean energy source • Abundant domestic source of energy – Wind resources in the Dakotas sum up to nearly 50% of US energy needs! • Renewable: – Solar heating of the atmosphere, earth rotation, and the earth's surface irregularities • Low cost: 4-6 cents/kWhr • Good for rural community development
- 5. Disadvantages • High initial investment • Intermittent source – Storage is a must! • Resources and load might not coincide • Land use • Noise, aesthetic impacts, bird-, bat kill
- 6. Vertical Wind Turbines Darrieus model
- 7. Alternative Energy Systems and Applications, B. K. Hodge, Wiley, 2010
- 8. Alternative Energy Systems and Applications, B. K. Hodge, Wiley, 2010
- 9. Vertical Axis Wind Turbines Advantages • Easier to maintain • No yaw mechanism • Higher airfoil pitch angle improved aerodynamics • Benefit from ground shape • Lower height • No free standing tower • Lower tip speed ratio not susceptible to cross winds • No orientation dependence • Lower ratio speed quiet operation Disadvantages • 50% the efficiency of HAWTs • Height limitation • Require relatively flat land • Low starting torque external excitation required! • Complex structure design • Lot of material per swept area
- 10. Wind Energy Engineering Tester et al. 2005 Power: force times velocity: P ~ v3 Mechanics Review F = m*a W = F*s; v = s/t P = W/t = F*v
- 11. Wind Energy Engineering Tester et al. 2005 Bernoulli Equation v2 /2 + g*z + P/ρ = constant
- 12. Tester et al. 2005 Wind Energy Engineering F = ρAt (vu – vd ) ( vu + vd)/2 comparing with earlier F equation vt = ( vu + vd )/2 P = 2 ρAt vt 2 ( vu – vt ) dividing above by total power in upstream air flow yields η = 0.593 Betz Limit
- 13. Betz Ratio • Maximum attainable efficiency for horizontal wind turbines ~ 59% – Assuming incompressible, irrotational, isentropic process .. Ideal flow – Some of the simplified assumptions penalize the conversion efficiency (no vortex shedding, no flow mixing) – Betz ratio is not a hard constraint • Current best practices: 50% wind to mechanical power and an overall efficiency of 40%
- 14. Alternative Energy Systems and Applications, B. K. Hodge, Wiley, 2010 Advance Ratio
- 15. Example of Actual Operation
- 16. Alternative Energy Systems and Applications, B. K. Hodge, Wiley, 2010 Weibull Distribution of Probability of Occurrence of Given Wind Speed h(v,k,c) = k/c (v/c)^(k-1) exp((-(v/c)^k)) c = scale parameter k = shape parameter Weibull Distribution
- 18. Horizontal Axis Wind Turbines • Anemometer – Wind speed measurements • Brake – Friction brake to stop the rotor in emergencies • Controller – Starts up Vwind ~ 8 to 16 mph and shuts off the machine at ~55 mph • Gear box – Increase rpm from ~50 to ~1500 – Should be removed in the future • Nacelle – Sits atop the tower and is the housing for gear box, low- and high-speed shafts, generator, controller, and brake • Pitch – Rotate blades to control the rotor speed • Tower – Made from tubular steel, concrete, or steel lattice • Wind vane: – Measures wind direction • Yaw drive – Only required for upwind turbines to keep the rotor facing into the wind as the wind direction changes
- 19. Wind Turbine Farms • Wind turbine grouping are better from a utility system operation point of view • Close spacing cause interference – Roughly: a unit 10 rows downstream at a spacing of 10D will yield 82% the power of the first row
- 23. GE 3.6 MW Annual average wind speed at hub height. Standard atmosphere according to DIN ISO 2533,M.S.L. Standard Rayleigh distribution and unobstructed air flow. http://www.gepower.com/prod_serv/products/wind_turbines/en/36mw/index.htm
- 24. Wind Energy Trends Annual Report on U.S. Wind Power Installation, Cost, and Performance Trends, 2006, US Dept. of Energy, EERE, Ryan Wiser, Mark Bolinger, May 2007 Growth is mainly due to: federal tax incentives, state renewable energy standards and incentives, and continued uncertainty about the future cost and liabilities of conventional natural gas and coal facilities
- 28. http://energy.gov/articles/new-interactive- map-shows-big-potential-america-s-wind- energy-future
- 30. Comparative Cost of Wind Power
- 31. Capacity Factors
- 32. Lessons Learned • Power ~ v^3 • Blade diameter governing factor • Betz factor • Turbine & system specs limit highest speed • Challenges in utilization • Cut-in/out speeds • Huge variation in torque – reliability • Ice formation • Distribution of wind power • Project Lessons
- 33. New Cost Models • http://www.nrel.gov/wind/pdfs/40566.pdf
- 36. Sustainability • Life Cycle Analysis – Net energy analysis roughly 1 year – Externalities • Aesthetic impact • Noise • Bird kill rate (endangered species hawks, eagles), bats – Negligible compared to the domestic cat! • Interference with radio and TV broadcasts • Land use • Maintenance worker hazards
- 37. Wind Quality • Density dependence on pressure and temperature should be considered (mountain tops (-10%), hot desert areas – 3%) • f(v) is the frequency spectrum of wind velocity • The best practice is to use the Weibull statistical function to curve-fit the measured wind velocities • (1/7) power low – From 30 to 50 m – 7.6% increase in v and 24.5% increase in Power 3 " 0.5P v f v dv 1 7 2 2 1 1 v h v h
- 38. Assignment What should we do? •# of turbines to replace conv. Power? •Feasibility (economic) •Optimum power •production (windspeed, cost) •Challenges competitiveness evaluation •Turbines in a farm: maximize production for given plot of land •Blade shape •Analysis of av. Windpower for different locations
- 43. Assignment 2 http://www.wind-energy-the-facts.org/en/part-i-technology/chapter-2-wind-resource-estimation/local- wind-resource-assessment-and-energy-analysis/the-annual-variability-of-wind-speed.html Data from NREL website: ftp://ftp2.nrel.gov/pub/ewits/TimeSeries/LandBased/2006/ Select Maryland and then a site in MD. Design a 1MW wind turbine and calculate how much power can be ideally produced…
- 44. Blade mass Fingersh et al., 2006 Wind turbine design cost and scaling model, NREL/TP-500-
- 45. Gearbox cost • Three-stage Planetary/Helical – Mass = 70.94*low-speed shaft torque0.759 – Total cost = 16.45*machine rating (in KW)1.249 • Single-Stage Drive with Medium-speed Generator – Mass = 88.29*low-speed shaft torque0.774 – Total cost = 74.1 * machine rating1.00 • Multi-Path with Multiple Generators – Mass = 139.69* low-speed shaft torque0.774 – Total cost = 15.26*machine rating1.249 Fingersh et al., 2006 Wind turbine design cost and scaling model, NREL/TP-500- 40566
- 46. Generator cost • Three-stage Planetary/Helical – Mass = 6.47*machine rating(in kW)0.9223 – Total cost = machine rating (in KW)*65 • Single-Stage Drive with Medium-speed Generator – Mass = 10.51*machine rating0.9223 – Total cost = machine rating*54.73 • Multi-Path with Multiple Generators – Mass = 5.34* low-speed shaft torque0.9223 – Total cost = machine rating*48.03 Fingersh et al., 2006 Wind turbine design cost and scaling model, NREL/TP-500- 40566
- 47. Alternative Energy Systems and Applications, B. K. Hodge, Wiley, 2010