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Deploying Tidal Energy Converters for electricity generation requires prior-knowledge of the potential Annual Energy Production (AEP) at the site, Ideally using a year-long tidal current record at the proposed site to minimize uncertainty. However, such records are often unavailable. Fortunately, using the periodic nature of tidal variability, the International Electrotechnical Commission Technical Specification for tidal energy resource assessment requires AEP calculation using at least 90 days of tidal current records at each turbine location. The sensitivity of AEP to different record durations has not been fully assessed. This is the goal of our study. The study utilized the U.S. tidal energy geodatabase to simulate tidal currents with various lengths, during 100 years of the 21st century. We then consider two frameworks for evaluating AEP: (a) The long-term (months) fixed instrument (FI) measurement at each proposed tidal turbine location, and (b) one FI measurement and short-term (hours) boat-based moving vessel measurements. Under the two scenarios, we examine the AEP assessed from short tidal current records, including how the AEP uncertainties vary spatially and temporally, and how they are associated with various astronomical factors. This helps provide guidance on choosing the appropriate assessment methodologies to reduce the AEP uncertainties and project cost. • The accuracy of annual energy production (AEP) estimation does not necessarily improve with longer tidal current records. • Computed AEP uncertainties are in resonance with relevant astronomical influences. • AEP assessment is improved by following optimal strategies for short record measurements. [ABSTRACT FROM AUTHOR]

The ocean contains a variety of renewable energy resources, little of which has been exploited. Here, we review both tidal range and tidal stream energy, with a focus on the resource, feedbacks, and environmental interactions. The review covers a wide range of timescales of relevance to tidal energy, from fortnightly (spring-neap) and semi-diurnal variability, down to array, and device-scale turbulence. When simulating the regional tidal energy resource, and to assess environmental impacts, it is necessary to account for feedbacks between the tidal array and the resource itself. We critically review various methods for simulating energy extraction, from insights gained through theoretical studies of "tidal fences" in idealized channels, to realistic three-dimensional model studies with complex geometry and arrays of turbines represented by momentum sinks and additional turbulence due to the presence of rotors and support structures. We discuss how variability can be reduced by developing multiple (aggregated) sites with a consideration of the enhanced phase diversity offered by exploiting less energetic tidal currents. This leads to future research questions that have not yet been explored in depth at first-generation tidal sites in relatively sheltered channels (e.g., the interaction of waves with currents). Such enhanced understanding of real sea conditions, including the effects of wind and waves, leads to our other identified primary future research direction—reduced uncertainties in turbulence predictions, including the development of realistic models that simulate the interaction between ambient turbulence and the turbulence resulting from multiple wakes, and changes to system-wide hydrodynamics, water quality, and sedimentation. [ABSTRACT FROM AUTHOR]

This study investigates the role of low-frequency cargo vessel wake to erosion at Bird/Long Island in the Savannah River, Georgia. The island splits the river into the Main Channel that accommodates cargo vessels traveling to the Port of Savannah, and the shallower, sheltered South Channel. Pressure and velocity data from both channels are used to characterize wind waves, tidal currents, and vessel wake. The relevance of each process to erosion is estimated by using hydrodynamic power as a proxy for erosive potential. Instantaneous water level is compared to the elevation of an eroding scarp to identify "scarp-relevant" power contributions, power occurring when the eroding scarp is at least partly submerged and susceptible to erosion. The analysis shows that scarp-relevant power in the Main Channel is dominated by cargo vessel wake (88%), with smaller contributions from tidal currents (5%) and wind waves (7%). Power in the South Channel is also dominated by cargo vessel wake (65%), followed by tidal currents (34%) and wind waves (1%). A follow-up study confirms that low-frequency cargo vessel wake, which produces waves heights up to 2.01 m in the Main Channel, propagates readily around both ends of the island and into the South Channel, where it produces wave heights up to 0.32 m. • Hydrodynamic power of tidal currents, wind waves, and cargo vessel wake was measured at two sites: one exposed, one sheltered. • Hydrodynamic power was used as a proxy for relative contributions to erosion. • Low-frequency cargo vessel wake was the main source of hydrodynamic power at both sites. [ABSTRACT FROM AUTHOR]

Tidal currents are a promising source for future power generation given their periodicity and predictability. Therefore, numerical hydrodynamic models are frequently utilized for resource assessments. However, the relevant scales of the simulations and hence modeling techniques depend on the problem at hand. This paper shows the potential of the grid refinement technique for the assessment of tidal current energy for particular sites given its relatively low computational expense and high accuracy for the regions with the refined resolution. Example applications are described for mapping the tidal resources near two facilities (Portsmouth Naval Shipyard in Maine and Key West Naval Station in Florida) for possible future deployments of Marine Hydro-Kinetic technologies. The grid refinement capability in the coupled ocean-atmosphere-wave-sediment transport modeling system is used to improve the spatial resolution in the regions of interest, and has shown significant advantage over the original simulation results for the tidal power assessment. The numerical simulation results from both the original coarse grids and the refined grids are validated with measured tidal constituents at available locations. This study demonstrates how the enhancement of a model system for a regional tidal energy with grid refinement can assist with the performance of site specific resource assessments with modest computational expense. [ABSTRACT FROM AUTHOR]

Abstract: A methodology for assessment of the potential impacts of extraction of energy associated with astronomical tides is described and applied to a site on the Beaufort River in coastal South Carolina, USA. Despite its name, the site features negligible freshwater inputs; like many in the region, it is a tidal estuary that resembles a river. A three-dimensional, numerical, hydrodynamic model was applied for a period exceeding a lunar month, allowing quantification of harmonic constituents of water level and velocity, and comparison to values derived from measurements, recorded at a location within the model domain. The measurement campaign included surveys of bathymetry and velocity fields during ebb and flood portions of a tidal cycle for model validation. Potential far-field impacts of a generic tidal energy conversion device were simulated by introducing an additional drag force in the model to enhance dissipation, resulting in 10–60% dissipation of the pre-existing kinetic power within a flow cross-section. The model reveals effects of the dissipation on water levels and velocities in adjacent areas, which are relatively small even at the 60% dissipation level. A method is presented to estimate the optimal vertical location for the energy conversion device and the potential power sacrificed by moving to a different altitude. [Copyright &y& Elsevier]

Energetic tidal streams are an especially attractive source of clean energy due to the daily occurrence of high tidal flows. However, before any deployment of tidal turbine farms, it is essential to perform a resource assessment depending on the scope and scale of the project. The International Electrotechnical Commission has developed a technical specification for assessing the tidal stream resource "IEC TS 62600-201" to aid in this effort: determine a particular site's feasibility and design the project layout. In this study, we implemented and validated a three-dimensional numerical model and provided results following the specification for a 'Stage 2' project layout design in a highly energetic tidal channel: Tacoma Narrows of Puget Sound, in the State of Washington, USA. Implementation of the numerical model based on the specification has helped estimate the annual energy production with higher model accuracy. We also used the same setup to evaluate the undisturbed theoretical and technical resources, where the latter included energy extraction from the flow field arranging a hypothetical tidal energy converter array. Ultimately, this work has shown the important role of the technical specification in larger project layout design, which can simultaneously act as a benchmark for other 'Stage 2' theoretical and technical resource assessment studies worldwide. • We conducted a 'Stage 2' tidal energy resource assessment following IEC Guidelines. • The Guidelines helped better predict the AEP required for project layout design. • The model validation and result reporting serve as a benchmark for future studies. [ABSTRACT FROM AUTHOR]

Numerical models have been widely used for the resource characterization and assessment of tidal instream energy. The accurate assessment of tidal stream energy resources at a feasibility or project-design scale requires detailed hydrodynamic model simulations or high-quality field measurements. This study applied a three-dimensional finite-volume community ocean model (FVCOM) to simulate the tidal hydrodynamics in the Passamaquoddy–Cobscook Bay archipelago, with a focus on the Western Passage, to assist tidal energy resource assessment. IEC Technical specifications were considered in the model configurations and simulations. The model was calibrated and validated with field measurements. Energy fluxes and power densities along selected cross sections were calculated to evaluate the feasibility of the tidal energy development at several hotspots that feature strong currents. When taking both the high current speed and water depth into account, the model results showed that the Western Passage has great potential for the deployment of tidal energy farms. The maximum extractable power in the Western Passage was estimated using the Garrett and Cummins method. Different criteria and methods recommended by the IEC for resource characterization were evaluated and discussed using a sensitivity analysis of energy extraction for a hypothetical tidal turbine farm in the Western Passage. [ABSTRACT FROM AUTHOR]