A general and widely applicable methodology to assess and present the performance of wave energy converters (WEC) based on sea trials is presented. It is meant to encourage WEC developers to present the performance of their WEC prototypes, on a transparent and equitable way while taking care of possible discrepancy in the observed performance of the WEC. Due to the harsh uncontrollable conditions of the sea that is encountered by WECs during sea trials, some of the performance of the WECs might be sub optimal and the data sets not fully complete. The methodology enables to filter the data by applying a selection criterion on the performance data that was obtained for a certain range of wave conditions. This selection criteria result in a subset of performance data representing the performance of the WEC for specific wave conditions, from which an average value an appreciation of the related uncertainty can be derived. This can lead to the estimation of the annual energy output of the WEC at its test location, while it also provides a method to estimate its annual energy output for another location of interest and possibly also at another scaling ratio. The same methodology can also be used to perform parametric studies with environmental or device dependent parameters and to analyse the power conversion chain from wave to wire, which both could lead to an enhanced understanding of the performance and behaviour of the WEC. The same methodology is also applicable to tidal devices or any other developing technologies that are used in an uncontrollable environment

Tidal Stream Turbines (TST) have the potential to become an important part of the sustainable energy mix. One of the main hurdles to commercialization is the reliability of the turbine components. Literature from the Offshore Wind sector has shown that the drive train and particularly the Pitch System (PS) are areas of frequent failures and downtime. The Tidal energy sector has much higher device reliability requirements than the wind industry because of the inaccessibility of the turbines. For Tidal energy to become commercially viable it is therefore crucial to make accurate reliability assessments to assist component design choices and to inform maintenance strategy. This paper presents a physics-based prognostics approach for the reliability assessment of Tidal Stream Turbines (TST) during operation. Measured tidal flow data is fed into a turbine hydrodynamic model to generate a synthetic loading regime which is then used in a Physics of Failure model to predict component Remaining Useful Life (RUL). The approach is demonstrated for the failure critical Pitch System (PS) bearing unit of a notional horizontal axis TST. It is anticipated that the approach developed here will enable device/project developers, technical consultants and third party certifiers to undertake robust reliability assessments both during turbine design and operational stages.

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As part of the ReDAPT, a project commissioned and co-funded by the ETI (Energy Technologies Institute), the first standard for certification of horizontal axis tidal turbine (HATT) has been commissioned to DNV GL in order to accelerate the development of the tidal technology and its commercialization. Although the development of the standard is limited to one turbine concept and unlike the wind turbines, the possible variations of configurations and the limited track record of the technology provided great challenges to define requirements and parameters to be considered in all aspects of the turbine. A risk based approach has been used on the different HATT configurations, addressing all the systems, subsystems and main components. The process, as described in the DNV OSS-312 – Certification of Tidal and Wave Energy Converters, addressing technology assessment and FMEA leading to a certification plan and definition of standards from Oil & Gas / Wind to be applied, was implemented in a level of detail sufficient to define the failure modes and associated risks that were the basis for definition of design, construction, commissioning and in-service life requirements. The work on failure modes and risks as well as data and definitions necessary for an effective risk based process were carried out with the support and assistance of ALSTOM during the ReDAPT project and the experience accumulated by DNV GL in the verification / certification projects carried out so far. Although every standard has a risk based background (even if based on field experience for many years), this standard has a direct connection between the identified risks and requirements. As the risks can vary for a specific configuration of HATT, technology matures and data is harnessed with the passing of the time, the approach used will allow for a faster and consistent adaptation of the standard now and in the future. This paper, describes the process in detail, presents the structure used for the risk assessment process, its conclusions and highlights the connection between the findings and the content of the standard.

One key aspect of serial production is to define a set of parameters that can define the limits and conditions that product can be used. Type certification is applied to serial production such as wind turbines when the matching of the site characteristics and the turbine design conditions is summarised in a short description of the site parameters that fundamentally describes the wind conditions (energy and turbulence). This easy matching is used by all stakeholders in assessing the suitability of different turbines to a specific project development. However, type classification is also important to optimise the design, manufacturing, installation and maintenance costs by setting key parameters to production of turbines with same characteristics (scale factor). The same applies to tidal turbines. Although, at the present phase of development, serial production is not yet a main driver and designs are mainly carried out with specific sites in mind, it is useful to develop a type classification now to support generic design parameters and that can be tested for future serial production and matching sites with serial products. While for wind turbines, the set of key parameters is reasonably simple [1], for tidal there are a number of environmental conditions (for example waves, astronomical tide, current turbulence, water depth, etc), and parameters (such as hub height related to the seabed and sea surface) which must be considered within the design of a HATT, parameters which may also be utilised in the construction of generic type classes for Tidal Turbines. Thus, the identification of generic type classes for HATTs is dependent upon the ability (by conjunction of assumptions, formulations, etc.) to distil the existing extensive list of site / HATT parameters down to a minimum number of key parameters upon which a simple but robust set of generic type classes could be based. Whilst it is recognised that adjustments of type classes may be required in the future, a first approach will be presented in the DNV GL Standard for Certification of HATT developed under the ReDAPT project and it is described in detail in this paper. The ReDAPT project is commissioned and co-funded by the ETI (Energy Technologies Institute).