Harnesting the Sea Breezes

I wasn't aware that there were wind generators stationed in the ocean. The windmills below are off the coast of Denmark. An obvious advantage is that the windmills don't take up land space. In all likelihood the same people who build offshore oil drilling rigs construct the sea-based windmills, I surmise, utilizing the same method of towing the upper structure to the site. The only difference is that I don't think the wind generators could be moored in very deep water.