With aspirations to claim 80 percent of its power from renewable sources by the 2050, it follows that Germany is taking a proactive approach to its clean energy transformation. Wind farms, while set to play an important part in achieving this goal, often meet impassioned opposition from disgruntled neighbors piqued by their perpetually blinking beacons. In an effort to address this issue, researchers have developed a sensor system for wind turbines which detects nearby aircraft, switching on a beacon warning system only as they approach.

Dubbed Parasol, the project is a collaborative effort from the Fraunhofer Institute, commercial concern Industrial Electronics and wind farm engineers Dirkshof Wind GmbH. Citing complaints of the beacons' incessant blinking from residents, though hamstrung by their necessity in preventing collisions with low-flying aircraft, the collective set to work in devising a solution which catered to all concerned.

By using passive radar sensors, meaning that they don't emit a radar beam themselves, the system is able to use local radio station frequencies to determine not only if there is an airplane in the vicinity, but its distance, position and velocity. According to Fraunhofer, the format of typical digital signals used by radio stations, such as DAB+ (Digital Audio Broadcasting) and DVB-T (Digital Video Broadcasting -Terrestrial), are useful in discerning between different objects and therefore well suited to this project.

Each of the system's three sensors attached to the mast has an antenna unit. Signal processing is undertaken within the mast and a CPU at each wind farm evaluates the data.

As the radio station's transmitters send out signals, these reflect off airborne objects. The system uses mathematical algorithms to differentiate between the reflections and the signal they would usually receive.

"The collision warning lights only switch on when an airplane is within a radius of four kilometers (2.5 miles) and flying below an altitude of about 2,500 ft (700 m)," says Heiner Kuschel, department head at Fraunhofer's Institute for High Frequency Physics and Radar Techniques. "We use the passive radar sensors to essentially extend a protective umbrella over the wind farm like a parasol."

The team has successfully tested a prototype at one of Dirkshof's wind farms at Reußen-Köge near Husum, and is currently optimizing the signal detection algorithms in anticipation of the system being fully operational by 2015.

"We hope that more local residents will agree to construction of wind farms through the installation of the collision warning lights," Kuschel continues. "The goal of Parasol is to advance the state of renewable energy and make Germany more competitive in the economic arena."

Source: Fraunhofer