Understanding Wind Power Technology: Theory, Deployment and Optimisation

11Offshore Wind Energy

Lothar Dannenberg

11.1 Offshore Wind Turbines

11.1.1 Introduction

As fewer places become available for siting onshore wind turbines (e.g. Germany, Netherlands) or wind conditions prove to be disadvantageous, many countries are being forced to install their wind turbines at sea (offshore). Pioneers of this at present are Denmark (in relatively near-coastal regions with shallow water depth: Horns Rev, at approximately 15 m depth) and the UK (near the coast).

In Germany there are great doubts about placing such plants near the coast because, to a large extent, these areas are nature reserves (Wadden Sea Nature Reserve), or for tourism reasons because of the ‘disturbing silhouettes’. For this reason, operators are forced to place offshore wind farms beyond the horizon, at distances of 30–120 km from the coast in water depths between 20 and 45 m. In the North Sea particularly, the conditions are almost as bad as deep-sea conditions, with wind and waves that are much stronger than in coastal regions.

Due to the environmental conditions and the great distances from the coast, the investments required for erection and servicing offshore wind turbines (OWTs) are very high. With the subsidies provided by the old German Renewable Energy Law (EEG) [Erneuerbare Energie Gesetz], this was not economical. This has changed with the updating of the EEG, but the grid operators have been additionally obliged to bear the costs of the connections to the grid from the wind farm.

However, ...