One could draw up an endless list of specialized and high-risk tasks that can be accomplished with helicopters, but given the current interest in renewable energy, yet another application has been implemented: servicing windfarms at sea.
The North Sea has been one of the "test benches" of wind energy production. A major early offshore windfarm installed in the North Sea is Alpha ventus, which was started in 2009 around 45 km offshore. “With 12 turbines of the 5MW type, it is more a test windfarm, which nevertheless was—and still is—an important project to learn from and transfer the knowledge to larger projects,” said Steffen Bechtel, director or windpark heliflight consulting. “In the meantime, the operators of Alpha ventus—E.ON, EWE, and Vattenfall—have installed other wind farms in the North Sea: Amrumbank West, Riffgat, and DanTysk.”
From the start, helicopters were used during installation, commissioning, and operation of the windfarms. “Helicopters serve for the transfer of personnel and cargo to the offshore substation [OSS], which is equipped with a helideck and the wind turbine generators [WTG]. Transfer to the WTG is only possible via helicopter hoist,” said Bechtel. “The passengers need special training for this type of transfer and there are specific requirements regarding the operator, the crew, and helicopter performance. Flying offshore in combination with helicopter hoist operations to wind turbines is one of the most challenging tasks one can find as a professional helicopter pilot. Qualifications like flying according to instrument flight rules [IFR], hoist operations, multi-pilot, and offshore operations are all required.”
The learning curve was steep and still is. Since transfering service technicians to the turbines and the OSS by boat is possible only up to a certain sea state, helicopters are used on a regular basis to ensure the continuing operation of the windfarms. In fact, from a wave height of around 1.5 m, the crew transfer vessels (CTV) can start to have problems holding a steady position on the foundation of the installations to safely disembark personnel. “The amount of flight hours and hoist cycles for a windfarm depends on various factors, but approximately 400 flight hours and over 1,500 hoist cycles per year is not unusual,” said Bechtel. “Alpha ventus is the smallest of the nearest windfarms to shore. All other wind farms are larger—with an average of 80 turbines—and farther offshore. The windfarm farthest offshore is Global Tech1, which has a manned OSS and 80 turbines of the 5MW-type. It is approximately 140 km northwest of Emden [Germany]. Helicopter hoist operations are performed almost daily. The OSS has a fueling facility and the helideck is equipped and approved for day and night operations.”
More than 38 wind farms with more than 2,000 wind turbines in the North Sea—as well as in the Baltic Sea—are approved by the German authorities and are in the planning or construction phase or are in operation. Almost all of them consider helicopters in their logistics concept. Most of the windfarms are in the North Sea, with 24 already installed or under construction with over 1,200 turbines and another seven in the planning or approval process (with more than 300 turbines).
Multiple operators serve the windfarms in the North Sea with hoist-equipped EC135s, H145s, AW139s, and AW169s, operating mostly from the shores of Germany. In recent years, while legacy offshore operations have gone through difficult times, the windfarm operators have experienced sizeable fleet expansions. The fact that an alternative to traditional offshore aviation has emerged offers some reassurance to the economic players of the helicopter industry. “Some two years ago, helicopter hoist operations to offshore windfarms also started in the UK. Denmark—where helicopter operations to offshore windfarms started in 2001 from the airport of Esbjerg to the windfarm Horns Rev—is already quite experienced in that area; but other European countries are about to catch up and are planning this type of operation in the near future,” concluded Bechtel.