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Flicker gopu

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  • 1. WIND TURBINE SHADOW FLICKER Prof. Gopu R. Potty, Ph.D. Department of Ocean Engineering University of Rhode Island Narragansett, RI 02882 potty@egr.uri.edu
  • 2. Shadow Flicker• occurs when the sun passes behind the rotors of  and casts a shadow over neighboring properties. • As the blades rotate, the shadow flicks on and off,  an effect known as shadow flicker.
  • 3. Shadow FlickerThe likelihood and duration of the effect depends upon: • Direction of the property relative to the turbine • Wind speed and direction • Distance from turbine • Turbine height and rotor diameter  • Time of year and day • Weather conditions (i.e. cloudy days) http://www.currentresults.com/Weather/Rhode‐Island/annual‐weather‐averages.php
  • 4. Shadow flicker is most pronounced in northern latitudes during winter months because of the lower angle of the sun in the winter sky. Shadows cast close to a turbine will be more intense, distinct and focused.
  • 5. Shadow Plots1 Day 1 year
  • 6. Health Concerns• Epileptic seizures  • typically by light flashes 5 to 30 Hz;  Wind turbine flicker if less than 1 Hz• Eye strain, headaches, nausea and  disorientation • mostly anecdotal evidence• Nuisance ‐ intrusive and annoying
  • 7. EXISTING GUIDELINES AND REGULATIONS Guideline or Regulation Germany 30 hr/year or 30 min/day Denmark 10 hr/year Netherlands 17 days/year or 20 min/day Massachusetts No Limit “minimize flicker” Maine No Limit “avoid unreasonable shadow flicker” New Hampshire 30 hr/year Ohio 30 hr/year Wisconsin 30 hr/year (mitigation required if greater than 20 hrs/year)
  • 8. Signal Interference• Signal blocking: – behind the turbine for a limited distance creating a  shadow zone – Shadow zone depends on  • material, geometry (height and width) of turbine• Signal Reflection – Reflection when structure is in line of sight to a  transmitter – Reflection depends on  • material, rotational speed of turbine, geometry and  orientation of blades relative to transmitter
  • 9. Technologies Affected• Television (ghosting) – Lower problem for digital signals • Satellite Television – Rarely a problem since signals are received from  very high• FM and DBA radio:  – Interference possible only within few 10’s of  meters• Scanning telemetry systems:  – Work in the UHF band and hence susceptible to  multi‐path effects from reflecting blades. • Fixed radio links:   – Public safety radio systems work using microwave  wavelengths can be affected when the wind  turbine is placed within the line of sight between  the transponder and a receiver 
  • 10. Cellular Phones• EM noise from turbines – insignificant – created is outside the cell phone band• Near field zone of transmitting and  receiving antennas is approx. 20 m.  – Objects within this zone can conduct or  absorb radio waves.• Diffraction: Partial or total blockage of  signal resulting in lower signal  strength.  – Problem when any object is within the first  Fresnel zone • Reflection: Caused when an object reflects  the waves.  – Less of a problem for blades made of glass  reinforced plastic and when the turbine is  separated from the tower by more than  325 ft.  
  • 11. Existing Guidelines• Setback distances are  generally not provided• Some guidelines requires  interference to be  considered and minimized.

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