The contractor put the last of the 80 monopiles in place on 22 July at the site, which is 32 kilometres west of the German island of Sylt.
Ballast Nedam's vessel, HLV Svanen, carried out the work within the four-month timescale. The monopiles themselves were transported from Esbjerg in Denmark.
Design of the foundations was completed in-house by Ballast Nedam Engineering, while other aspects of construction and logistics were handled by Ballast Nedam Offshore.
Work on the transition pieces is now going ahead, with 50% of them installed.
The water depth at the project ranges from 17 to 22 metres. It will be made up of 80 Siemens 3.6MW turbines and is due to go online next year.