Sensitivity of Risk-Based Maintenance Planning of Offshore Wind Turbine Farms

Abstract

Inspection and maintenance expenses cover a considerable part of the cost of energy from offshore wind turbines. Risk-based maintenance planning approaches are a powerful tool to optimize maintenance and inspection actions and decrease the total maintenance expenses. Risk-based planning is based on many input parameters, which are in reality often not completely known. This paper will assess the cost impact of this incomplete knowledge based on a case study following risk-based maintenance planning. The sensitivity study focuses on weather forecast uncertainties, incomplete knowledge about the needed repair time on the site as well as uncertainties about the operational range of the boat and helicopter used to access the broken wind turbine. The cost saving potential is estimated by running Crude Monte Carlo simulations. Furthermore, corrective and preventive (scheduled and condition-based) maintenance strategies are implemented. The considered case study focuses on a wind farm consisting of ten 6 MW turbines placed 30 km off the Danish North Sea coast. The results show that the weather forecast is the uncertainty source dominating the maintenance expenses increase when considering risk-based decision-making uncertainties. The overall maintenance expenses increased by 70% to 140% when considering uncertainties directly related with risk-based maintenance planning.

Statistical and synoptic analyses of offshore wind variations

“…In addition to limiting power production, episodes of high wind speeds and severe weather conditions impose practical challenges related to the access of offshore wind farm sites for the purpose of construction or maintenance (Breton and Moe, ). Accessibility to offshore structures by workboats is mainly limited by the significant wave height, which depends on fetch length, fetch duration, and wind speed (Ambühl and Sørensen, ). A wind speed of 11 m/s can be accompanied by significant wave height of 3 m (Beaufort scale).…”

“…A wind speed of 11 m/s can be accompanied by significant wave height of 3 m (Beaufort scale). According to Ambühl and Sørensen (), the common maximum significant wave height for operational boats servicing wind farms is 1.5 m. In stormy conditions when the wave height is larger than the maximum wave height of operational boats, a helicopter is usually used to access offshore turbines, which involves higher costs, and can be risky to workers in high wind speed conditions. The common maximum operational wind speed of helicopters is 20 m/s.…”

IEA Wind TCP: Results of IEA Wind TCP Workshop on a Grand Vision for Wind Energy Technology

“…Important for both fixed and floating systems is the development of O&M procedures that are smarter, requiring less work at sea, and the development of designs that better facilitate cost-cutting O&M strategies. This includes feedback from optimizing maintenance and inspection regimes into the design process to achieve material savings while guaranteeing the structural reliability over the wind farm lifetime (Ambühl and Sørensen 2017). Some substructure concepts allow for disconnecting the platform from its moorings and towing it back to a harbor, which may be a safer and cheaper alternative for major component replacement.…”

An effective approach for robust design optimization of wind turbine airfoils with random aerodynamic variables

“…Rather than assuming that the aerodynamic parameters are deterministic, measurements for C l and C d have shown uncertainties in the wind tunnel test. 16,17 This motivates the use of a probabilistic model to quantify the design optimization of airfoils in this article. The influence of uncertain geometry parameters on the lift and drag coefficients was investigated by Ernst et al, 18 whereas Sørensen and Toft 19 presented a risk-informed framework for probability-based design optimization of wind turbine structures.…”