Offshore Wind Farms (OWFs) have rising importance for energy provision of many regions worldwide. However, their harsh environment leads to considerably higher failure rates and degradation compared to its onshore counterparts. Consequently, OWFs require well-established maintenance processes in order to provide required operational availability of all wind turbines. Amongst the several factors impacting these processes the personnel plays an important role, bearing in mind that no maintenance is possible without having access to technicians or seamen operating the required vessel. This work proposes a comprehensive model for evaluating the actual impact the personnel availability has on the corrective maintenance processes of an OWF and, consequently, its energy production. Therefore, maintenance processes and WT failure rates based on reported data are considered. Furthermore, a pandemic model is employed in order to elaborate the possible impact a health crisis can have on the operational availability of an OWF. Results indicate that the monthly energy production can drop by up to 74% in case of a constant reduction of the personnel by 50%, while a worst case pandemic scenario results in a 23% lower energy production over the whole year.

The share of wind power generation is steadily increasing and it reached 20.4% of Germany's power supply in 2018. Thus wind power is becoming a critical infrastructure with major contributions to power supply and power system grid stability. Consequently a resilient operation of offshore wind farms (OWFs) is required under normal and disturbed conditions. Resilience stands for the ability of a complex system to proactively and reactively maintain its functionality and performance despite failures or manipulations. A functional model describes the technical behavior of engineered, cyber-physical systems in relation to the intended task or results of the system. It is a representation of the operation, functionality and performance of the system, e.g. in the form of a block diagram. The block diagram consists of components performing, according to their technical characteristics, specified functions on the inputs. Applied to the OWF the components can be grouped into several layers representing the main functional processes. Within this paper we consider the threat of system failures triggered through cyber-physical attacks, based on the vulnerability of the OWFs to such attacks as documented in the literature. Most of the main functional processes can be manipulated maliciously. The functional model is used to discuss the impacts of different scenarios of cyber-physical attacks and their resulting cascade effects, which may cause a non-resilient behavior of the OFW. Crucial parameters and signals can be manipulated maliciously. Limit thresholds can be exceeded by far even under normal environmental and power grid conditions. Excessive mechanical stresses, electrical and thermal loads can be realized, leading to extreme damage or even destruction of components/subsystems without the possibility of reactive intervention or timely recovery. We propose measures on component and functional level for closing the mentioned security gaps to ensure the resilience of the OWF.

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