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Here’s some good news: There’s enough wind energy blowing across the oceans on our planet to power all of humanity. So say Anna Possner and Ken Caldeira of Stanford University, who authored “Geophysical potential for wind energy over the open oceans,” published in August 2017.
The two academics are optimistic about the future of the offshore wind energy industry internationally, and in Europe specifically.“Even in the relative calm of summer, the upper geophysical limit on sustained wind power in the North Atlantic alone could be sufficient to supply all of Europe’s electricity,” they write.
The offshore advantage is obvious: Wind is weakened on land by obstacles both natural and man-made, from mountains to skyscrapers, but the oceans present no such problems. They do, however, offer challenges that engineering, technology and logistics have to deal with.
THE CONSTRUCTION CHALLENGE:
In the Baltic Sea and the North Sea, the critical elements for a sustainable future in energy generation are being put in place using two supply ships driven by MAN engines. The names of the ships reflect the global nature of the industry:
One is the Pacific Orca, the other the Pacific Osprey. Both undertake the complex offshore operations involved in the erection of wind turbines. “The vessels have a flexible diesel electric system that provides up to 24 MW of power,” says Christian Kamm, Sales Manager at MAN Diesel & Turbo, before outlining an array of impressive specs. “To handle these heaviest of wind offshore components, they are equipped with a 1,200-metric-ton and 1,425-metric-ton main crane capable of operations both above and below sea level,” says Kamm of the Orca and Osprey. “For working in a harsh offshore environment, they have 6-x-105-meter lattice legs, a fast, electric rack-and-pinion jacking system, and spudcans designed to handle a range of seabed conditions.”
Jurik Kiewit, Branch Manager Wind at RENK, is very familiar with the offshore world. “The operational expenditure for offshore turbines is extremely high. If a gearbox fails onshore, it’s a pain to deal with, but having to change one out at sea is a real nightmare. In the industry, it’s really no secret that over 70% of gearbox failures are due to ordinary roller bearings.
We reduce those failures with our slider bearing technology, and therefore also reduce operational costs.” RENK gearboxes were first installed in offshore wind turbines over 14 years ago – and they are still running reliably today. “The industry has only recently recognized that slide bearings provide a more reliable solution, and is now slowly shifting to this technology,” he adds. “We’re the only manufacturer with such a solid track record, with over 200 units successfully installed.”
The real horror scenario of any wind farm operator is downtime. Stig Holm, Head of On-site Recovery, MAN PrimeServ Copenhagen, is the go-to person when it comes to discussing the most common offshore turbine problems and the turnaround time in solving them. “Generator shaft repairs top the list of offshore turbine issues,” he says without hesitation. “We also polish brake discs. Rotating towers are equipped with braking systems analogous to those used in cars, and sometimes the surface of the disc gets worn and we polish it up to the previous surface state.”
To eliminate downtime, it requires a head for heights in the harshest of environments at sea, a strong skillset in engineering and the ability to work flexibly under time pressure. Speed is always of the essence, as Holm confirms. “We can move at very short notice,” he says. “Altogether, from when we leave our company, until the job is completed, whether it is onshore or offshore, it is about four to five days total, for traveling, repair and returning.”
When technicians are needed at sea, service vessels take center stage. “For short distances, smaller Crew Transfer Vessels are used; for longer trips, more specialized Wind Service Operation Vessels (WSOVs). These WSOVs are driven by several GenSets, providing diesel-electric power for more hotel load, crane capacities and dynamic positioning mode,” says MAN’s Christian Kamm. Crucial for the service engineers is also a comfortable ride, and a safe and secure transfer.
Out in the middle of the ocean, this requires a vessel capable of precise maneuvering in precarious conditions. Recently, MAN has equipped a newly designed 83-meter WSOV with variable medium-speed GenSets for Louis Dreyfus Armateurs, the French shipowner, for wind farms in the North Sea. The engines can be equipped with MAN’s own SCR system to reduce emissions and meet IMO Tier III standard. As the costs for setting up offshore turbines continue to decrease, and the 2020 deadline for achieving the European Union’s target of meeting 20% of its total energy needs with renewables approaches, such vessels are part of an array of sustainable solutions that will help meet the challenges of the forces of nature out at sea.
We can move at very short notice and need four or five days to finish the job.
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