Offshore wind turbines have been used for decades to harness air movement to generate energy. To maximize power output, wind turbines must be built further offshore as the wind is both stronger and more consistent there. But moving further offshore also means deeper waters which pose additional challenges – both for engineers and operators. The solution: Floating wind farms that are not fixed to the seabed like conventional offshore wind turbines but anchored with special mooring systems. One example of this construction method is the Hywind Tampen project in the North Sea, the world’s largest floating wind farm.
Like putting eleven Eiffel Towers on the High Seas
"Each wind turbine is about as high as the Eiffel Tower and consists of three sections: The floating concrete substructure, the tower, and the actual turbine, as we know it from onshore sites, with 81.5-meter long rotor blades. These are really large dimensions we are talking about", explains Sigbjørn Birkenes, OMV Senior Project Manager in Norway. One of the technical challenges in the engineering and design was the substructure of the wind turbines. Project engineers with oil & gas competence and background from platform engineering were particularly valuable to overcome this challenge. The substructure consists of a hollow concrete column (a "Hull") that floats in the water and is tethered to the seabed with anchoring lines at depths of up to 300 meters. Currently, seven of the eleven wind turbines are on the Tampen location producing green electricity to the Gullfaks field. The last four turbines will be installed in the summer period. "The individual wind turbines are one kilometer apart. The whole wind farm when completed is so big that we will not be able to capture it entirely in a single photo without using aerial photo devices", Birkenes says.
The Hywind Tampen floating offshore wind farm reduces the carbon footprint of the Gullfaks field and is also an ideal testbed for developing the construction and operation of offshore wind farms in the future.
Sigbjørn Birkenes, OMV Senior Project Manager in Norway
How to build the world's largest floating wind farm
"You can compare it to a Lego game. The parts are delivered individually, and we have assembled them with one of the largest land cranes ever used in Norway ", explains Sigbjørn Birkenes. Instead of assembling it in the middle of the open sea in heavy wind and high waves, the assembly takes place in a designated base near the coast. "We are lucky to have such deep fjords in Norway", explains Birkenes. "This way, we can assemble the huge wind turbines along with the massive substructure, and then use anchor handlers to pull them out to their final location". That is 140 kilometers off the Norwegian coast, between the two oil and gas fields, Gullfaks and Snorre in the North Sea.
“The Gullfaks field (OMV’s stake 19%), previously generated its own electricity using gas turbines directly on the platform. To reduce emissions, alternative energy sources were considered. Furthermore, we wanted to remain self-sufficient in terms of energy and continue to generate electricity whenit is needed. Approximatively 30% of the electricity used on the platform now comes from wind power and is supplied to the platforms via a network of cables. Altogether, almost 60 kilometers of special cables have been used”, Birkenes adds.
Pioneering work for the future
"This is the first time ever that a floating wind farm has been connected to oil and gas platforms. With this, we are reducing the emissions with around 200,000 tons of CO2 per year, which is equivalent to emissions from 100,000 cars", Birkenes points out. "We can also learn a lot about the supply of power grids and the interaction between hydrocarbons and renewable energies. Moreover, we can further explore the use of larger turbines, innovative installation methods, simplified moorings and concrete substructures for future projects".
"The oil and gas industry has a long tradition in Norway and will continue to play an important role whether it is for energy use or feedstock for plastics”, he says. “My teenage daughters often can’t relate to my job as a project manager in an oil & gas company because of our fossil fuel production. But when I talk about our efforts to lower our carbon footprint with emission reduction and sustainable energy solutions like Hywind Tampen, we can agree that our industry has some future perspectives that move us in the right direction”, concludes Sigbjørn Birkenes.