Although floating technology for wind farms is relatively new, it is rapidly gaining interest among developers due to its potential to overcome the limitations of conventional offshore turbines and meet challenging climate targets. Floating projects, anchored to the seabed by mooring lines, are more suitable for countries with limited access to shallow waters, or where the geology of the seabed makes it impossible to install conventional ‘fixed-bottom’ turbines. These are difficult to install beyond depths of 60m, which makes them unsuitable for waters further from shore, where wind speeds are higher.
The UK – home to Hywind, the world’s first commercial floating wind park – has a 1GW floating target out of a total 40GW offshore wind goal by 2030. Countries such as France, Norway, Spain, the USA and Japan – surrounded by deeper waters than the North Sea – are now actively pursuing floating technology.
Connection challenges
The installation of floating wind turbines presents numerous challenges for those active in the industry, including IQIP, a partner to many of its leading contractors. One such hurdle on the Hywind project was how to provide an efficient method for mating two structures, namely the tower section with the floating substructure, without human interaction. While the industry is constantly seeking to improve safe working practices, the need for a solution arose due to changes to UK legislation stipulating that people must not work under suspended loads.
For the Hywind project, five turbines were first assembled at a quay in a Norwegian fjord before being towed into position 29 km off the Scottish coastline. Due to the challenges of wave conditions and movements, it was decided to build the turbines onshore and install them on the fjord.
The use of floating substructures means that the longer equipment stays connected with a vessel, the greater the safety risks, and the higher use of fuel through the dynamic positioning of the vessel. So time, money and sustainability are also significant factors.
Many things are involved in the installation and if the process can be expedited, several issues can be eliminated. It’s important to consider that there are several sequences in the process, from securing the turbine before lift-off, remote release and then connection to the floating structure, transit from installation to the floating quay, and securing the turbine during bolting.
As five turbines were required, making a series installation without the interference of (manual) bolting actions (which can take two to three hours) was the optimum solution. There is also a limited timeframe for the installation and contractors must wait for good weather with no waves. Time is a major influence.
