Sea ice and icing risk for offshore wind turbines

There are two important issues related to wind turbines performances in offshore sites that locate in cold climates: sea ice (flows, driving ice, land-fast ice) and the presence of atmospheric icing (due to water in the air as in-cloud operation, rainfall and sea sprays) which may potentially lead to ice formation on turbines’ structures. Icing of rotor blades and some other wind turbine components have effect on the design of turbines, the safety of O&M personnel and the overall economics of a wind energy project. In offshore conditions ice pack or floating blocks on the sea surface cause additional static and dynamic forces on the turbine structure. The effects of sea ice occur as a mechanical shocks and increased vibrations that may result to additional operational loads. The presence of sea spray, associated with atmospheric icing, determines complex icing phenomena that are highly dependent on the elevation of the turbine rotor over the sea level and on the size and type of wind turbine. Therefore a risk analysis needs to be performed to assess the life reduction and the hazard of ice shedding which is relevant to neighbour turbines and O&M personnel. Ice mitigation systems should comprise cold weather packages, anti-icing/de-icing devices and systems reducing the actions of sea ice. The design of such systems should be integrated in the design of the turbine to assess the economic benefit of their operation in cold climates and to set limits for continuous operation during icing periods. The paper presents a general framing of the icing phenomenon for wind turbines in offshore sites and a procedure for analyzing the risk of ice pieces shedding from the turbines A general scheme of a procedure for the integrated design of ice mitigation systems for wind turbines is also presented and discussed.