Offshore wind energy company SWAY reports that extreme weather caused its floating wind tower test model to sink into the sea last weekend.
The down-scaled 1:6 test model is located at a site outside Bergen, Norway, and has been surveyed by an ROV. According to SWAY, there were no visible structural damages, and the test model will be recovered soon, after which time the company will assess how long repairs will take.
The direct cause leading to the sinking of the prototype was extreme weather exceeding the design parameters, SWAY says. Due to its size, the scale model was designed for a maximum wave height of four meters, which represents full-scale waves with a maximum wave height of 26 meters.
Data collected by the National Renewable Energy Laboratory at the site shows a maximum wave height for the scale model of 6.3 meters, which would translate to 40.6 meters in full scale. These wave conditions are extreme – in comparison, the North Sea the "hundred year wave" is just 30 meters.
This extreme wave height, combined with a storm surge, caused water to enter into the tower through the inlet pipe for the power cable (the J-tube), causing the tower to fill with water, SWAY explains. The J-tube will be extended to eliminate this risk before the 1:6 scale model is redeployed, the company adds.
Even though the effect of the extreme storm would not be a problem for a full-scale turbine, the company says it has learned from this incident.