Wind energy is the clear front running renewable energy source as wind power installations have become the second largest contributor to installation of electricity capacity in the EU over the last decade , . Technological advancement in the design of wind turbines has allowed for the introduction of higher capacity turbines with towers exceeding 100 meters in height. The global installed offshore wind base, in particular, is expected to grow from 3.9 GW to nearly 45 GW in 2020.
Although offshore wind has the potential to deliver the highest quantities of energy, it is not yet competitive with onshore wind mainly due to higher Operating & Maintenance (O&M) costs and the plausible risk of lower availability due to difficulties in obtaining access to the wind turbines during bad weather.
According to a 2011 Wind Energy Operations Maintenance Report offshore wind turbines O&M costs are 2 to 6 times higher than on-shore wind turbines, while 66% of these costs are caused by unscheduled, corrective maintenance. This figure could be spiked by an additional 20% over the short term, as innovative 7 MW, variable-speed and direct-drive designs enter the market. Component failure, logistic equipment costs, weather, and a general lack of understanding of O&M cost correlation to shore distance are just a handful of factors acting against offshore O&M budgets. Although tower structure failures represent only 5% of total failures, they are responsible for more than 22% of the associated downtime.
In light of this, technical and economical efforts should be directed at achieving the optimal structural performance over the life of the wind turbine. The deterioration processes, such as degradation, fatigue and corrosion, typically affect offshore structural systems. This damage decreases the system’s performance and increases the risk of failure, thus not fulfilling the established safety criteria. Avoiding failures altogether is clearly the best way to limit O&M costs.