NEEDS-BASED WARNING LIGHTS ON WIND TURBINES
The energy transition focuses increasingly on wind energy as an alternative, CO2-neutral source of energy. But not everyone is impressed with this method of energy production. The anti-collision lighting on the turbine cabins blinks continuously through the night and is a disturbance to the local community. A needs-based lighting system controlled by environmentally-friendly passive radar technology should help to remedy the situation.
To prevent collisions, wind power installations that exceed a certain height have to be fitted with anti-collision lighting to ensure that they can be identified by low-flying aircraft. The blinking red lights are a source of disturbance to the local residents and also attract birds who are often killed as a result of a collision with the rotor blade of a wind turbine. Hence, there is now a great demand for warning lights that are only switched on when an aircraft approaches the vicinity of the wind turbines. To realize this, flight activity near the wind turbines must be recorded and analyzed.
Fraunhofer FHR was commissioned by the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety to develop a needs-based control system for anti-collision lights on wind turbines.
The PARASOL project
In the PARASOL project (German acronym for passive radar-based control of object identification for aviation), approaching aircraft are detected using passive radar sensors that do not emit any radar radiation, but rather use existing radio signals to locate planes. The protection range of a passive radar network spans over the entire wind farm like a parasol. This method is characterized by its environmental compatibility. It is also cost-effective and, in contrast to other active methods, a transmitting license is not required.
Fraunhofer FHR has many years of experience in the field of passive radar, in particular, through the use of the modern digital radio networks DVB-T and DAB+. Compared to other radio and communication signals, these are particularly suitable for the passive radar sensors that are used in the PARASOL project as the radio transmitters bundle their signal energy at low heights (below 1000 m) and the transmitted signal forms and processing algorithms are suitable for distinguishing between different objects.
The utilization of the PARASOL system for as-needed anti-collision lighting on wind turbines will enhance the acceptance of wind farms, further promote the use of renewable energies and therefore strengthen Germany as an industrial location in the long term.
How passive radar systems work
Signal processing in passive radar systems is based on the correlation of the signal that is received directly from the transmitter with its reflections on moving objects. Due to the movement, these echo signals experience a frequency shift (Doppler effect) as well as – depending on the location of the object – a time delay compared to the direct signal. The location and speed of the object can be determined from an evaluation of these measured values and the direction from which the echo signals are coming.
When using digital radio signals, the transmit signal can be ideally reconstructed based on the knowledge of the signal synchronization characteristics. In the Federal Republic of Germany, these networks are, however, operated as single frequency networks, i.e. all transmitters in the network coherently transmit the same signal at the same time, and special efforts are therefore required to allocate the correct target echo to the respective illuminating transmitter.
Realization of passive radar systems
The hardware components for passive radar systems that use digital radio signals (DAB+, DVB-T) can be designed in a compact and – when ordered in larger quantities – cost-effective manner. The development in the IT sector supports the trend towards miniaturization. Antenna systems that are capable of blanket monitoring (360°) and are suitable for integration into existing infrastructures, e.g. wind turbines, can also be realized. Passive radar systems can therefore be used in a highly flexible manner in a wide range of application areas.