Hydrodynamic modelling is an important tool for the development of tidal stream energy projects. Many hydrodynamic models incorporate the effect of tidal turbines through an enhanced bottom drag. In this paper we show that although for coarse grid resolutions (kilometre scale) the resulting force exerted on the flow agrees well with the theoretical value, the force starts decreasing with decreasing grid sizes when these become smaller than the length scale of the wake recovery. This is because the assumption that the upstream velocity can be approximated by the local model velocity, is no longer valid. Using linear momentum actuator disc theory however, we derive a relationship between these two velocities and formulate a correction to the enhanced bottom drag formulation that consistently applies a force that remains close to the theoretical value, for all grid sizes down to the turbine scale. In addition, a better understanding of the relation between the model, upstream, and actual turbine velocity, as predicted by actuator disc theory, leads to an improved estimate of the usefully extractable energy. We show how the corrections can be applied (demonstrated here for the models MIKE 21 and Fluidity) by a simple modification of the drag coefficient.
Coastal and Offshore Energy
The North Seas offshore grid serves to connect offshore wind power to onshore systems, and to interconnect power systems in Northern Europe. Its development is a priority for the European climate and energy policy, which has led to a number of studies on the subject. Nonetheless, research questions, assumptions and typologies can vary considerably among them, and thus to guide future research this paper reviews the published works that use bottom–up energy models. This review develops a simple and effective methodology that can be applied to other reviews of energy systems models. It jointly considers the studies of interest, the system characteristics, a categorization framework and relevant indicators. The analysis indicates most studies focus on investment and operation of the grid using optimization models, with rare use of other research questions or other model approaches. Moreover, results vary significantly, and their comparability is limited due to differences in assumptions, methodology and detail of results publication. Nonetheless, integrated typologies frequently present economic, operational and environmental benefits, although the reviewed studies do not unambiguously warrant immediate and full cooperation on grid governance. Lastly, future research should be attentive to the presentation and resolution of data, assumptions and results, as well as consider grid characteristics relevant to the research questions.
The emerging ocean energy industry, which seeks to utilise waves and tides to generate electricity, is developing in many jurisdictions. The UK, and Scotland in particular, is strongly interested in these technologies, and has made considerable efforts to reform its marine governance processes to better meet the needs of innovative new marine industries. This paper provides an industry perspective on this regulatory framework, reporting on the experiences of ocean energy project and technology developers. Semi-structured interviews with companies with practical experience with Scotland's regulatory framework provide evidence of a number of legal and regulatory challenges, as well as interesting insights into how developers are interacting with new marine governance systems. The paper details the findings of these interviews and offers some suggested directions for future research.
The oceans of the earth offer vast amounts of renewable energy. Technologies to harness the power of the seas are at an early stage of development. Even the most advances technologies, namely tidal current and ocean wave still face considerable barriers and many obstacles remain. Research, development and innovation can help overcome those barriers. This review provides an overview over the current state of research in the field of ocean energy. In particular, the authors focus on research beyond technology or technological improvements. This article also highlights areas where research gaps exists and where future research efforts should be directed to.
This paper aims to identify institutional improvement measures to promote environmentally sustainable ocean renewable energy development by analyzing how the environmental assessment systems in South Korea are integrated into this development. The measures identified in the paper include (1) consideration of subjecting ocean renewable energy development to strategic environment assessment in order to assess the adequacy of relevant project plans and the validity of site selection at early stages, (2) new standards, such as the area of occupancy, integrated within the environmental impact assessment at the project implementation stage, (3) integration of the environmental impact assessment with the procedures for Consultation on Utilization of Sea Areas to reduce development cost and delays and (4) reinforcement of post-development environmental monitoring processes to eliminate uncertainty or lack of knowledge about potential impacts on marine environment and habitat caused by development.
A 14-year high resolution wave and wind hindcast was carried out for Ireland. The wind was dynamically downscaled from the ERA-Interim reanalysis to a 2.5 km horizontal resolution and 65 vertical levels, using the HARMONIE meso-scale model. The wave hindcast was derived using WAVEWATCH III on an unstructured grid with resolution ranging between 10 km offshore and 225 m in the nearshore, forced by the downscaled HARMONIE 10 m winds and ERA-Interim wave spectra. The wind and wave hindcasts were thoroughly validated against available buoy data, including wave buoys in nearshore locations and coastal synoptic stations. In addition, the significant wave heights and winds from the hindcasts were compared against all available altimeter data from the CERSAT database at Ifremer. The quality of both the wind and wave hindcasts was found to be good.
The wave and wind energy resource in coastal areas was assessed, and discussed in terms of water depth, distance to shore, and seasonal and inter-annual variability. In addition, the current study investigates the nearshore wind and wave climate in conjunction with each other, and highlights two issues with relevance to the ocean renewable energy industry: (i) the complementarity between the wind and wave energy resource, and (ii) the accessibility for marine operations. Our study highlights sites around the Irish coast that might have been overlooked in terms of the potential for wind, wave or combined wind/wave energy installations.
In Chapter 1, a fully-coupled (hydrodynamic and morphologic) numerical model is presented, and utilized for the simulation of tsunami-induced scour around a monopile structure, representative of those commonly utilized as offshore wind turbine foundations at moderate depths i.e. for depths <O(30 m). The model is based on solutions to Reynolds-averaged Navier-Stokes equations, coupled with two-equation k-ω turbulence closure, with additional bed and suspended load descriptions forming the basis for sea bed morphology. The model is first validated for flow, bed shear stresses, and scour within a steady current, where a generally excellent match with experimentally-based results is found. A methodology for maintaining and assessing hydrodynamic and morphologic similarity between field and (laboratory) model-scale tsunami events is then presented, combining diameter-based Froude number similarity with that based on the dimensionless wave boundary layer thickness-to-monopile diameter ratio. This methodology is utilized directly in the selection of governing tsunami wave parameters (i.e. velocity magnitude and period) used for subsequent simulation within the numerical model. The flow, sediment transport, and scour processes beneath three tsunami waves are simulated in succession. These illustrate a generally accumulative scour process i.e. a relatively rapid scour induced by the leading wave, with an additional buildup of the scour depth during additional trailing waves. The resulting scour seems to approach an equilibrium value after sufficient time duration, which corresponds reasonably to that predicted by existing steady-current scour depth, after invoking a boundary layer thickness based on the unsteady tsunami wave, i.e. it is important to incorporate both current-like, as well as wave-like aspects of the long tsunami event. Based on the simulated results, a simple methodology for predicting the scour depth in engineering practice is finally developed. This methodology is demonstrated to match the predicted maximum scour for all of the simulated flows considered i.e. ranging from the series of transient tsunami waves to the steady-current limit. In Chapter 2, the aim is to provide an overview on the tsunami impacts on aquaculture rather than presenting a comprehensive review on the status and trends in aquaculture development. [For such a comprehensive review the reader is referred to the FAO (Food and Agriculture organization of the United Nations) report titled “The State of the World Fisheries and Aquaculture” released in May 2014.] For this purpose, we first briefly provide and introductory summary on aquaculture. This is followed by the section “Vulnerability of Fisheries and Aquaculture Systems” where the main focus is the vulnerability to tsunamis. Next, tsunami Impacts on aquaculture are exemplified based on the major tsunami events that occurred since 2000s. Later, specific case studies highlighting different aspects in aquaculture design are illustrated in the section “Engineering Design of Aquaculture Systems”. In Chapter 3, tsunami impact on coastal ecosystems is investigated. Ecosystems along the coast of Portugal are considered and a detailed numerical modelling of tsunami impact is performed for the Ria Formosa lagoon (an important ecosystem located in the southern coast of Portugal). The tsunami modelling is carried out using a validated non-linear shallow water numerical code. A high resolution digital elevation model (50m-resolution) of the zone of interest is used to properly simulate the tsunami hazard. The active earthquake sources of the southwest Iberia Margin (SWIM) region represent the tsunamigenic scenarios in this study. Tsunami impact at the Ria Formosa lagoon is assessed through deriving near-shore tsunami wave heights, inundations, and flow velocities. Numerical results show that the Ria Formosa lagoon can suffer powerful tsunami impact due to the occurrence of a tsunami event in the SWIM region.
This paper is a compilation of potential and current best practices for addressing interactions and supporting successful cooperation between commercial fishing and offshore wind interests. It is intended, generally, to contribute to the growing knowledge base on this important topic and, specifically, to serve as a resource for discussions among industry and government parties in New England. Information for the paper was gathered from the United Kingdom—where the historically strong fishing industry and the offshore wind industry have a long track record of interactions—the Block Island Wind Farm, and other locations with relevant experience. The resulting compendium of best practices identifies a set of commonly-held concerns and offers corresponding tools and practices for addressing them.
With several offshore wind farms currently under consideration off the U.S. Atlantic seaboard, offshore wind has the potential to be an abundant source of renewable, low carbon electricity. Island communities throughout New England are leading the way in developing effective approaches for engaging with offshore wind developers. The report highlights key insights for designing good community engagement processes and demonstrates these best practices through case studies from Block Island (RI), Martha’s Vineyard (MA), and Monhegan (ME).
An Offshore Wind Energy Geographic Information System (OWE-GIS) has been developed for the purpose of assessing the economically accessible offshore wind energy resource for the United Kingdom.
The UK OWE-GIS estimates the costs of energy from an offshore wind farm taking account of the major capital components; development costs dependent on water depth and distance from nearest ports or grid connection points; the potential energy production dependent on annual average wind speed, potential array losses, and turbine availability; operations and maintenance costs; and financial parameters such as discount rate and project lifetime. A sensitivity analysis is presented to show the influence of discount rate, project lifetime, and assumptions about overall capital expenditure (CAPEX), availability, and annual mean wind speed.