Borgen (Sway) Copy_Outsourcing_book_temp.qxd 02/03/2010 16:41 Page 53
Floating Wind Power in Deep Water – Competitive with Shallow-water Wind Farms?
further out to sea in stronger winds with a corresponding increased just as was the case for the monopile solution for fixed foundations, did
annual energy yield from the turbines; at the same time, the turbines not offer sufficient stiffness and strength to be cost-effective for
will not be visible from shore, reducing issues of public conflict. This is, turbines in the 4–5MW range and above. In particular, fatigue of the
of course, good news for all of the countries mentioned at the towers has proved to be challenging for the floating towers and
beginning of this article, and countries such as Spain, the US, Japan, foundations due to the additional motion and inertia forces
Korea, Norway, etc., are actually very well positioned to play a strong compared with a fixed tower. At the same time, it was understood that
role in harvesting offshore wind. it was critical to be able to install turbines in the 5–10MW range to bring
down the cost of energy in the future.
Just as the monopile is the most cost-effective solution for small turbines
on fixed foundations, the patented Sway elongated floating monopile Sway’s solution to this was to locate the yaw bearing, which is normally
seems to be the most economical solution for floating foundations for positioned at the top of the tower, at the bottom of the tower instead,
such that the entire tower would ‘weather-vane’ using a down-wind
orientated turbine and always keep the same side of the tower towards
the wind. This made it possible to equip the tower with wire bracings
Most of the planned large
(see Figures 2 and 3) on the upwind side of the tower, just like the wire
offshore windfarms in Europe
stays of a sailboat mast, increasing the stiffness dramatically and at the
same time eliminating the problem of fatigue in the tower. The Sway
will be located in fairly deep
solution is therefore able to use the cost-effective floating monopile
water of 20–30m or more.
concept for turbines of 5–10MW and above.
The technology for cost-competitive floating wind turbines has already
been developed. The next three to four years should be used to
small turbines. When Sway commenced its development of the floating construct and operate full-scale prototypes and small pre-commercial
monopile in 2001, it was based on the very low fabrication costs of such floating windfarms. The reward of a successful deployment programme
designs compared with the more complex semi-submersible truss will be that in the future practically all countries with access to either
structures, as well as the good motion characteristics. However, it was shallow or deep water with good wind resources will be able to
quickly realised that for larger turbines the floating monopile solution, economically tap into the unlimited clean energy of offshore wind. n
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