# Decision Support Models for Operations and Maintenance for Offshore Wind Farms: A Review
## 6 Data Sources and Availability of Data
### Data in the Literature
#### 6.1.2 Failures  
Data for failures are especially hard to find, since most manufacturers do not want to make their numbers public and because operators often do not have the complete failure history of their turbines. For onshore wind farms, failure data is easier to find than for offshore wind farms. The problem with using the failure rates of onshore turbines, when modeling offshore wind farms, is that offshore turbines often are of different types than onshore turbines and harsher weather conditions offshore lead to increased degradation and different failure causes than onshore. Data from onshore wind farms can be found in [114; 115; 116; 117; 118; 119; 120]. [PERSON] et al. [115] provide data from onshore wind farms on failure rate and sub-assembly reliability. They also provide a taxonomy for turbine sub-assemblies. A homogeneous Poisson process model is used to calculate the probability of failures from the MTBFs. They use data collected over 10 years in Germany and Denmark and assume that the failures are i.i.d. exponentially distributed. Sub-assembly failure rates and MTBF are provided for 12 sub-assemblies. [PERSON] et al. [116] present a failure modes and effect analysis for onshore wind turbines. They present data from a real 2 MW turbine (V80). 107 turbine parts, 16 failure modes and 25 root causes and present the top 10 for each category. [PERSON] et al. [117] provide a turbine taxonomy and reliability database listing fault events, failure rates, downtime, wind farm figuration and additional turbine information. They present the normalized failure rates for subsystems and assemblies of multiple manufacturers as well as the normalized hours lost due to the faults. Mean annual failure rates are available from [PERSON] et al. [118] for different turbine subsystems. The annual failure rates and downtimes per failure have been calculated based on the data from 1500 wind turbines that were monitored between 1989 and 2006. [PERSON] et al. [114] report the MTBFs for onshore turbines. [PERSON] et al. [119] present common failures and failure frequencies as well as annual availability numbers for Chinese onshore wind farms. [PERSON] et al. [120] in their paper give failure rates and downtimes for 4300 onshore turbines in the Mediterranean region. Data from offshore wind farms is reported by [107; 108; 109; 121; 4; 122]. [PERSON] and [PERSON] [121] provide a formula to calculate failure rates and present example failure rates, for offshore wind turbines. Data from Egmond aan Zee wind farm collected by NoordzeeWind has been reported for three consecutive years in [107; 108; 109]. [PERSON] et al. [4] report operational performance such as availability and energy yield for four different UK offshore wind farms. [PERSON] et al. [122] present failure rates for \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Publication** & **ECMWF [105]** & **FINO [106]** & **Others** \\ \hline \hline  & & & NoordzeeWind [107; 108; 109] \\ [PERSON] et al. [11] & & ✓ & Centre for Environment, Fisheries and Aquaculture Science (CEFAS) [110] \\  & & & British Oceanographic Data Centre (BODC) [111] \\ [PERSON] et al. [12] & ✓ & & \\ [PERSON] et al. [14] & & ✓ & \\ Feuchtwang and Infield [61] & & & Barrow and Scroby Sands wind farms \\ [PERSON] et al. [15] & & & EKLIMA [112] \\ Hofmann and Sperstad [16] & & & Offshore oil platform \\ Endrerud and Liyanage [21] & & ✓ & \\ [PERSON] et al. [20] & & ✓ & \\  & & & Le Havve airport (wind speed) \\ [PERSON] et al. [22] & & & Rayleigh distribution [114] \\  & & & (wave height) \\  & & & Uniform distribution (lightning) \\ [PERSON] and [PERSON] [36] & & ✓ & \\ [PERSON] and [PERSON] [101] & ✓ & & \\ [PERSON] et al. [26] & & & Wavewatch III [113] \\ [PERSON] and [PERSON] [65] & ✓ & ✓ & \\ [PERSON] and [PERSON] [66] & & ✓ & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: This table summarizes which weather data has been used in the different models. 19 turbine components and four types of repairs/replacements.