HOW THE ROC ANALYSES WIND TURBINE SITING PROPOSALS

The ROC learns of wind farm developments through both formal and informal methods. Formally, the Department of Commerce’s National Telecommunications and Information Administration (NTIA) acts as clearinghouse for developers to voluntarily submit wind farm proposals for review by several federal agencies, including NOAA. This formal process is recognized by the wind industry in the American Wind Energy Association’s (AWEA) Wind Siting Handbook (AWEA 2008). Informally, the ROC occasionally receives notifications directly from developers, or learns of wind farm projects from local forecast offices who email news articles or web links to stories about planned wind farms. The ROC typically receives 10 to 15 notifications per month through the NTIA and 1 to 3 per month directly from developers or third parties. The ROC tries to proactively contact the developers if a third party notifies the ROC of a wind project that has the potential to significantly impact a nearby WSR-88D.

Based on the wind farm proposal the ROC receives, the ROC provides a case-by-case analysis of potential wind farm impacts on WSR-88D data and forecast/warning operations. The ROC uses a geographic information system (GIS) database that utilizes data from the Space Shuttle Radar Topography Mission to create a RLOS map with delineated areas corresponding to a turbine height of 160 m AGL. Multiple radar elevation angles are considered for projects close to the radar.

The ROC then performs a meteorological and engineering analysis using: distance from radar to turbines; maximum height of turbine blade tips; the number of wind turbines; radar azimuths impacted; elevation of the nearby WSR-88D antenna; an average 1.0 degree beam width spread; and terrain (GIS database). From this data the ROC determines if the main radar beam will intersect any tower or turbine blade based on the Standard Atmosphere’s Refractive Index profile.

Finally, the ROC estimates operational impacts based on amount of turbine blade intrusion into RLOS, number of radar elevation tilts impacted by turbines, location and size of the wind farm, number of turbines, orientation of the wind farm with respect to the radar (radial vs azimuthal alignment), severe weather climatology, and operational experience. The ROC also compares the wind farm to other operational wind farms to estimate impacts.

The ROC has developed a four zone scheme that takes terrain, distance, and the number of elevation angles impacted into account while. The four zones use terminology that communicates to wind farm developers the desired action. These zones, defined below, are: no build, mitigation, consultation and notification. The No Build Zone is a 4 km radius red circle around the WSR-88D. The ROC is requesting that developers do not build turbines in the RLOS within 4 km of the radar due to the potential for serious impacts, including turbine nacelles blocking the radar beam and potential receiver damage if sited in the radar’s near field. The Mitigation Zone, orange areas on the map, is the area between 4 km and 36 km where a 160-meter turbine would penetrate more than one elevation angle. Wind farms sited within the mitigation zone have the potential for moderate to high impacts. Therefore, the ROC will work with the developer to get detailed project information, do a thorough impact analysis, and discuss potential mitigation solutions. The Consultation Zone, yellow areas on the map, is the area between 4 km and 36 km where a 160-meter turbine only penetrates the 1st elevation angle or when a 160-meter tall turbine will penetrate more than one elevation angle between 36 km and 60 km. Due to the increased potential for impact to operations the ROC is requesting consultation with the developer to track the project and acquire additional information for a thorough impact analysis. The Notification Zone, green areas on the map, is the area between 36 km and 60 km where a 160-meter tall turbine will only penetrate one elevation angle, or any area beyond 60 km that a 160-meter tall turbine is in the RLOS. Since impacts are typically minimal beyond 60 km and workarounds are available for penetration of only one elevation angle, the ROC is making consultation optional; however, NOAA would still like to know about the project.

The figure depicts an example of the primary categories of wind farm analysis requests/replies.

  

An example radar line of sight (RLOS) map generated by the NEXRAD ROC for a wind farm analysis. Four hypothetical proposals: W, X, Y, and Z as described in the text are shown.

Wind Farm A: clearly out of the RLOS, would have no impact on the radar data, except in some anomalous propagation conditions, in which case impacts would be low. Wind Farm B: Notification zone - low impact on the radar data if turbines were built in the western portion of the proposal area. The ROC would suggest that the developer locate most/all wind turbines in the western portion of the proposed area. Wind Farm C: Consultation Zone - low impact on the radar data if turbines were built in the western portion of the proposal area. The ROC would suggest that the developer locate most/all wind turbines in the western portion of the proposed area. Wind Farm D: Mitigation Zone - low to moderate impacts on the radar. The ROC would seek to consult with the developer to determine if there is flexibility to consider impact mitigation techniques and to ensure the developers are aware of potential impact on forecast/warning operations. Wind Farm E: Encroaches into No-Build Zone. Potentially high impacts on the NEXRAD for the portion of the proposal in the red area. The ROC would seek to consult with the developer to ensure they are aware of the likely impact on forecast/warning operations, the NEXRAD system, and the wind turbines/personnel.