The offshore wind version of an arms race is well underway. The current leader: A joint venture between Japan’s Mitsubishi Heavy Industries and Denmark’s Vestas Offshore Wind announced in January that its latest generation wind turbine had smashed through the 9MW barrier, less than a year after the industry’s first 8MW generators were commercially installed.
Wind turbines rated 10MW and higher are near at hand. Denmark’s Dong Energy said in April that it expects 13MW to 15MW turbines to be operational by 2024, the year the company plans to launch three offshore wind farms in the German North Sea.
“Offshore wind technology is moving faster than even turbine manufacturers believed” five years ago,” said Feng Zhao, a senior director at FTI Consultancy and one of the firm’s experts on wind energy. As recently as 2012, 2MW generators were the industry standard.
Now, three manufacturers – MHI Vestas Offshore Wind, Siemens Wind Power and Gamesa-owned Adwin – all offer 8MW turbines. (Spanish company Gamesa and Siemens merged in April.)
The industry isn’t just moving toward larger and larger turbines for bragging rights, or even because a particular sized offshore wind farm can yield more electricity. As a percentage of total project costs, installing a turbine offshore is far higher than onshore. This means that the more electricity generated by an individual turbine, the less number of total turbines need to be installed. That translates as well into less cable costs, less foundation costs, less costs for delivery vessels, less time for installation, in effect generating power for less money.
Advances in drive technology account for some of the increases in turbine size. The bigger turbines use direct drives, eliminating gears. Gearless turbines are lighter. They also reduce operations and maintenance costs, removing the need, for example, for oil changes that can cause environmental damage.
In 2016, about 25% of wind turbines installed used direct drives, according to FTI.
Bigger turbines, of course, mean bigger blades. The latest generation MHI Vestas turbine stands 220 meters tall. It turns blades that are 80 meters long each and weigh 33 tons. Advanced composites assist the production of larger blades.
Obviously, transporting these overland would pose enormous logistical challenges. So, most blades are manufactured in facilities that are both dockside and relatively close to the wind farm being developed. For example, MHI Vestas blades are being manufactured at a facility on the Isle of Wight just upriver from the sea. The first two projects using these blades are in the Irish Sea.
Installing the bigger turbines also places huge demands on delivery and installation vessels. Floating vessels aren’t a viable alternative for next-generation installation, according to Erik Snijders, founder and managing director of the Rotterdam-based offshore consultants SeaOwls. That’s because of excessive motion due to wind and waves, which would endanger installation of nacelles and blades.
A joint venture between SeaOwls and the Norwegian shipbuilders Ulstein Group unveiled in February a new jack-up vessel specifically designed for 10MW to 15MW turbines. The vessel will have the ability to transport anywhere from three to six blades at one time, with a crane capable of lifting 1,250 tons as much as 200 meters from sea level.