• Energy Research
• GB close
• Renewable Energy close
• European Marine Science close

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.

Turbulence is a crucial flow phenomenon for tidal energy converters (TECs), as it influences both the peak loads they experience and their fatigue life. To best mitigate its effects we must understand both turbulence itself and how it induces loads on TECs. To that end, this paper presents the results of blade element momentum theory (BEMT) simulations of flume-scale TEC models subjected to synthetic turbulent flows. Synthetic turbulence methods produce three-dimensional flowfields from limited data, without solving the equations governing fluid motion. These flowfields are non-physical, but match key statistical properties of real turbulence and are much quicker and computationally cheaper to produce. This study employs two synthetic turbulence generation methods: the synthetic eddy method and the spectral Sandia method. The response of the TECs to the synthetic turbulence is predicted using a robust BEMT model, modified from the classical formulation of BEMT. We show that, for the cases investigated, TEC load variability is lower in stall operation than at higher tip speed ratios. The variability of turbine loads has a straightforward relationship to the turbulence intensity of the inflow. Spectral properties of the velocity field are not fully reflected in the spectra of TEC loads.

Abstract Geographical Information Systems (GIS) are commonly used in renewable energy resource analysis to establish optimal locations for development. Previous work focuses either on a single technology with fixed site-selection criteria, or on small, localised areas. The potential for combining or co-locating different offshore energy technologies, particularly over a large region, has been explored previously but at a relatively low level of detail. Here, bespoke resource data from high resolution co-located, co-temporal wind and wave models are presented in a GIS with a range of additional environmental and physical parameters. Dedicated decision-support tools have been developed to facilitate flexible, multi-criteria site selections specifically for combined wind-wave energy platforms, focusing on the energy resources available. Time-series tools highlight some of the more detailed factors impacting on a site-selection decision. The results show that the main potential for combined technologies in Europe is focused to the north and west due to strong resources and acceptable depth conditions, but that there are still obstacles to be overcome in terms of constructability and accessibility. The most extreme conditions generally coincide with the maximum energy output, and access to these sites is more limited.

Abstract This paper introduces a new approach for investigating trade-offs between different societal objectives in the design of tidal-turbine arrays. This method is demonstrated through the trade-off between the yield of an array, and the extent to which that array alters the flow. This is posed as a multi-objective optimisation problem, and the problem is investigated using the array layout optimisation tool OpenTidalFarm. Motivated by environmental concerns, OpenTidalFarm is adapted to not only maximise array yield but also to minimise the effect of the array upon the hydrodynamics of the region, specifically the flow velocity. A linear scalarisation of the multi-objective optimisation problem is solved for a series of different weightings of the two conflicting objectives. Two idealised test scenarios are evaluated and in each case a set of Pareto solutions is found. These arrays are assessed for the power they generate and the severity of change they cause in the flow velocity. These analyses allow for the identification of trade-offs between these two objectives, while the methods proposed can similarly be applied to the two key societal objectives of energy production and conservation, thus providing information that could be valuable to stakeholders and policymakers when making decisions on array design.

This paper presents a refined description of the wave climate observed in a Portuguese location for marine energy projects. The data used in this case study were derived from 3-month in situ measurements carried out using three directional buoys that have been deployed simultaneously – yet independently (various buoy types and water depths) – on the Atlantic coast in the neighbourhood of Figueira da Foz. Two ways of reporting the statistics were adopted. In the first one, each recorded sea state was summarized as a set of global parameters accounting for energy, mean frequency and direction, spectral bandwidth and directional spreading related to the main ongoing wave field considered as unimodal. In the second one, each sea state has been decomposed into its own wave components – swells and wind-sea – which are characterised separately and individually by the same set of parameters as previously. Besides the adopted data processing techniques and the illustration of such thorough wave climate description modes, the paper also addresses the advantages and limits of each adopted parameterization in the frame of simultaneous and independent in situ wave measurements.Highlights► Wave statistics produced considering unimodal and multimodal sea-state descriptions. ► Spectral bandwidth and directional spreading are included in both descriptions. ► Spectral bandwidth is significantly correlated to wave energy/peak period. ► Wave directional spreading is difficult to estimate in absolute terms. ► Directional artefacts are obtained with Maximum Entropy Methods in some cases.

As the marine renewable energy industry evolves, in parallel with an increase in the quantity of available data and improvements in validated numerical simulations, it is occasionally appropriate to re-assess the wave and tidal resource of a region. This is particularly true for Scotland - a leading nation that the international community monitors for developments in the marine renewable energy industry, and which has witnessed much progress in the sector over the last decade. With 7 leased wave and 17 leased tidal sites, Scotland is well poised to generate significant levels of electricity from its abundant natural marine resources. In this state-of-the-art review of Scotland's wave and tidal resource, we examine the theoretical and technical resource, and provide an overview of commercial progress. We also discuss issues that affect future development of the marine energy seascape in Scotland, applicable to other regions of the world, including the potential for developing lower energy sites, and grid connectivity.