The usage of machine learning techniques is widely spread and has also been implemented in the wind industry in the last years. Many of these techniques have shown great success but need to constantly prove the expectation of functionality. This paper describes a new method to monitor the health of a wind turbine using an undercomplete autoencoder. To evaluate the health monitoring quality of the autoencoder, the number of anomalies before an event has happened are to be considered. The results show that around 35% of all historical events that have resulted into a failure show many anomalies. Furthermore, the wind turbine subsystems which are subject to good detectability are the rotor system and the control system. If only one third of the service duties can be planned in advance, and thereby the scheduling time can be reduced, huge cost saving potentials can be seen.Energies 2020, 13, 1063 2 of 18 With the model developed, a deviation from normal behavior can be considered as an anomaly. This paper aims to evaluate the anomalies generated by a NBM before a failure has occurred at the WT. These failures are documented in the form of service reports.A literature review is given in Section 2. Hereafter, the NBM is described and trained in Section 3. In Section 3.1, the basic functionality of an Autoencoder (AE) is briefly explained. Data is needed to train the model. This data is described in Section 3.2. Adjustments to the data, filtering and fine-tuning of the parameters of the AE are to be explained in Section 3.3. Thereafter the output of the model as well its usage is presented in Section 3.4.In Section 4, the steps in order to derive a clean failure dataset are shown. Information about downtime events are extracted out of maintenance documents and the measures undertaken at the WT and its components translated into standards (Sections 4.1 and 4.2). To ensure the correctness of the downtime events, we explain how they will be validated in Section 4.4.With the usage of both, the historical failures of the WT (Section 4) and the trained model (Section 3), the time window before the occurrence of a failure can be investigated. This is conducted in Section 5. Subsequently, the detectability of WT failures can be evaluated (Section 5.2). The potential scheduling time and the subsystems with failures are considered to be potentially good detectable in advance. To have a holistic approach, also anomalies during expected normal behavior, are to be investigated. The results are discussed in Section 6 and concluded with Section 7.