Following promising results from demonstration projects, the next stage in the development of tidal stream energy is the commercial exploitation of this resource. Many high energy density tidal sites are in interconnected channels and hence an interaction between nearby tidal farms is expected. In this study, the impacts of farm interactions are analyzed based on changes in the capacity factor and the length of offshore work windows estimated using results from a three-dimensional numerical hydrodynamic model. This study focuses on four nearby farms in the Goto Islands: two farms that are side-by-side in the same channel, and two other farms that are in parallel channels. The side-by-side farms reduce each other’s capacity factor by 5.37% and 2.22% due to velocity deficits in the turbine wakes of the adjacent farm. This decrease in current velocity leads to an increase in the length of offshore work windows, as these windows are defined by periods for which the current velocity at the turbine installation points is below a given threshold. Conversely, the interactions of farms in parallel channels are negligible in the case of the Goto Islands. These results highlight the importance of considering inter-array interactions to maximize energy generation and minimize installation and maintenance costs.

To reach the objective of net-zero carbon by 2050, Japan is promoting the development of renewable energies. Among these, tidal current energy provides high predictability and stability, which can help mitigate the negative impact of the high variability of other sources (solar, wind) on the grid management. As an initial step for the design of a tidal current energy national development plan, this paper presents a resource analysis for South - West Japan. Results for current velocity from an ocean numerical model were used to identify tidal energy sites and estimate the theoretical resource for each of them. Applying the same ocean model results to the specifications of nine turbines, energy output was estimated for each site. Results showed an estimated installable capacity of 4,422.5 MW and an annual energy yield of 8,956.06 GWh. More than 78% of this resource is allocated in only six areas or sites: the straits between Goto Islands, the entrances to Ariake Sea, Hayasui Strait, Kurushima Strait, Bisan Strait, and Naruto Strait. Though this work provides valuable insights for the theoretical and technical resource in South - West Japan, further research is needed to evaluate the economical viability of tidal energy exploitation in each site.

Tidal stream energy technology has progressed to a point where commercial exploitation of this sustainable resource is practical, but tidal physics dictates interactions between tidal farms that raise political, legal and managerial challenges that are yet to be met. Fully optimising the design of a turbine array requires its developer to know about other farms that will be built nearby in the future. Consequently future developments, even those in adjacent channels, have the potential to impact on project efficiency.Here we review the relevant physics, consider the implications for marine policy, and discuss potential solutions. Possible management paths range from minimal regulation to prioritise a free market, to strongly interventionist approaches that prioritise efficient resource use. An attractive exemplar of the latter is unitization, an approach to resource allocation widely used in the oil and gas industry. We argue that an interventionist approach is necessary if the greatest possible energy yield is to be produced for a given level of environmental impact.

The Alaska coast not only has the largest regional wave resource, but also has one of the top tidal-stream energy hotspots in the US: the Cook Inlet. The development of wave and tidal energy projects relies on consistent and accurate resource characterization using fine-resolution model simulations at potential project sites. This study a comprehensive modeling effort on wave and tidal energy resource characterization in Alaska. Specifically, the wave energy resource characterization was based on a 32-year high-resolution regional wave hindcast using two widely used phase-averaged models, WaveWatchIII and SWAN. WaveWatchIII was configured with three-level nested grids from global to regional scales, with the finest grid resolution of 4-arc-minute. The SWAN model, implemented on an unstructured grid, was configured with a spatial resolution of approximately 300 m in the nearshore and 30 km offshore …

© 2017 Elsevier Ltd The authors regret that a software error caused incorrect predictions for the effects of tidal turbines in Delft3D. The predictions without turbines are unaffected, as are those from the MIKE 3 model. The overall conclusions of the article remain valid. Figs. 12–15 as published are incorrect. Replacements for Figs. 12–14 are presented here. Following this correction the differences in the effects of energy extraction between the two models are much smaller. As a result the discussion of these differences in Section 6 should be disregarded, and Fig. 15 is no longer required. The authors would like to apologise for any inconvenience caused. The version of the code for adding turbines to Delft3D that is publicly available has been corrected, and anybody using this for their own work is urged to download the latest version. [Figure presented] Fig. 12: (a) 400 turbines in the Inner Sound, viewed through the MIKE Zero GUI; (b) The same 400 turbines represented as porous plates for Delft3D. Higher values of the closs parameter, shown by bluer colours, indicate plates with higher drag. [Figure presented] Fig. 13: Changes in mean current speeds over 28 days as a result of adding turbines. [Figure presented] Fig. 14: Change in mean bed stress magnitude over 28 days as a result of adding turbines, expressed as a proportion of the value without turbines.

The Goto Islands in Nagasaki Prefecture, Japan, contain three parallel channels that are suitable for tidal energy development and are the planned location for a tidal energy test centre. Energy extraction is added to a 3D numerical hydrodynamic model of the region, using a sub-grid momentum sink approach, to predict the effects of tidal development. The available resource with first-generation turbines is estimated at 50-107 MW peak output. Spreading turbine thrust across the whole cross-section to prevent bypass flow results in a 64% increase in peak power in one channel, highlighting the importance of 3D over 2D modelling. The energy available for extraction in each strait appears to be independent of the level of extraction in other straits. This contrasts with theoretical and numerical studies of other multi-channel systems. The weak interactions found in this study can be traced to the hydraulic effects of energy extraction not extending to neighbouring channels due to their geometry. (C) 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license.

As part of the Terawatt project, two regional-scale hydrodynamic models of the Pentland Firth & Orkney waters were developed using unaltered commercially-available software (MIKE 3 and Delft3D), in order to investigate the suitability of such software for predicting the effects of tidal stream energy development. Realistic scenarios for tidal energy extraction were implemented in each, and the predictions of the models with and without turbines compared. Similar predictions were made of depth-averaged current speed (spatial correlation of R2=0.95), but bed stress in one model was more than double that in the other due to the use of different values for bed resistance. The effects of energy extraction are consistent between the models at a regional scale but show considerable local differences. We conclude that these model codes are suitable for broad-scale assessment of the effects of energy extraction but that caution, and more detailed survey data, is required at fine scales.

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.

•We describe a modelling project to estimate the potential effects of wave & tidal stream renewables on the marine environment.•Realistic generic devices to be used by those without access to the technical details available to developers are described.•Results show largely local sea bed effects at the level of the currently proposed renewables developments in our study area.•Large scale 3D modelling is critical to quantify the direct, indirect and cumulative effects of renewable energy extraction.•This is critical to comply with planning & environmental impact assessment regulations and achieve Good Environmental Status.

Two commercial packages were employed to model tidal turbines in Lashy Sound – a strait in the Orkney Isles of Scotland in which Scotrenewables plans to build a 30MW tidal farm. These two models use different approaches and assumptions, and have historically been used in very different ways at very different resolutions to one another. Recently, both types of model have been used at resolutions in the range 10-100m [1, 2] to model tidal energy extraction.