Offshore wind power plants are typically installed along coastlines, where average wind speeds are high and port facilities are within reach. The seabed must also be suitable, i.e. firm and sandy, and establishing a grid connection must be possible.
Most feasible areas are typically within a couple of kilometres of the coast. The sheltering effect of land means that the most powerful wind resource is presumably onshore wind.
More information
Horns Reef: View the construction of one of the world’s largest offshore wind power projects (approx 5 min.)
North Hoyle: View the construction of the UK’s first major wind power project off the north coast of Wales (approx 9 min.)