Over the past several years, wind turbine blade construction has advanced considerably, moving from an aluminum composition (prone to reflect and scatter radio signals) to a much more “radio friendly” construction of fiberglass composites. Despite these advances, “big wind farm” developers still face two challenges with signal interference:
1) Radar interference
Wind farm turbine blades are known to interfere with the radar tracking of weather systems and airplanes. The tip of a turbine blade may reach 170 MPH creating “doppler clutter” and cause the radar to misinterpret the data it is receiving. For example, a weather radar may reflect the wind shear between the fast moving blades as a tornado. An air traffic control radar, on the other hand, may temporarily lose track of an aircraft flying near to or behind a wind farm’s blades. In 2008, the Department of Homeland Security commissioned a study that stated “Despite these difficulties, there is no fundamental physical constraint preventing detection and mitigation of windmill clutter. The technologies of wind turbines and radar can coexist.” (http://www.fas.org/irp/agency/dod/jason/wind.pdf)
2) Digital Television and Radio Interference
Transmitter interference is driven by many variables including the TV receiver location in relation to the wind farm and the transmitter, the proximity of a wind farm to the transmitter, the frequency used and the receiver technology. Wind farms have been known to cause interference to over-the-air (OTA) digital television signals. A DTV signal passing through a wind farm turbines’ blades to a distant receiver can be met with issues inside the TV receivers’ internal circuitry causing pixilation, or no picture at all. Depending upon the projected level of interference, a wind farm developer may need to purchase cable or satellite services for neighborhoods whose OTA signal will be impaired following a wind farm’s construction. Click on this youtube video to see a clip from our latest DTV interference research : http://www.youtube.com/watch?v=qcTMQ1C3TEI&context=C329e979ADOEgsToPDskLiDaypwDS7pPZBQmLqx4Pp
While somewhat more resilient than DTV signals, microwave signals and their paths must be fully evaluated during a wind farm’s planning stages.
AM radio transmission is highly susceptible to interference by turbine towers constructed close to the transmitter site. The rule of thumb for developers is to construct the turbine(s) at least 1 kilometer away from the AM antenna array (3 km’s for directional antenna settings). When you build a turbine close to an AM station you will also need to take worker safety precautions to prevent electrical burns. Take a look at this 1 minute video taken at a construction site < 1 km from an AM antenna: http://www.youtube.com/watch?v=iiirMEdiJQI&feature=plcp&context=C3145d56UDOEgsToPDskIrBDFS6gKJt2QimZehRcSn
Traditional (analog) FM radio is far less susceptible to wind farm interference, given the nature of the FM radio receivers’ circuitry.
This wind solar facility in Atlantic City, New Jersey has 3 FM stations co-located among the blades of the turbines. The stations’ Chief Engineer reports that he has seen no interference issues in the 5 years that the turbines have been in operation.
Needless to say, all wind farm planning must include a complete RF interference study to identify all potential interference to RF, establish a solid baseline and to mitigate problem areas prior to construction.
Distributed wind typically involves a standalone turbine and has far less potential to cause radar, radio or TV interference. Small wind systems (less than 100 kW) are shorter and less massive and typically don’t affect military radar. Increasingly, small wind power is being deployed to power television, radio and telecommunications transmission sites. Companies like Ericsson, Vodacom and Motorola are researching and implementing wind power for the next generation of remote towers.
Some stations are already powering their entire transmitter operation on renewable energy. KRNG-FM serving Fallon, Nevada has it’s 1.9 kW ERP transmitter situated 7,000 feet high on top of Two Tips Mountain. Utility power is not available here. The transmitter is powered soley by renewable energy including a 10 kW Bergey Excel wind turbine, a large solar panel and a battery room for energy storage.
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For much more information on Wind Energy / TV and Radio Interference: www.BroadcastWind.com