Abstract
As devices move from full-scale prototype to commercial installations, it is important that developers have detailed knowledge of the tidal energy resource. Therefore, the spatial distribution of the tidal currents over the northwest European shelf seas has been examined to improve understanding of the tidal-stream energy resource. Using a three-dimensional hydrodynamic model (ROMS) at ∼1 km spatial resolution, and applying device characteristics of the Seagen-S turbine, we show that the ratio of the amplitudes of the M2 and S2 tidal currents can lead to significant variability in annual practical power generation – variability that is not accounted for when considering only the mean peak spring tidal velocities, as is generally the case in resource feasibility studies. In addition, we show that diurnal inequalities (governed by K1 and O1 tidal constituents) and tidal asymmetries (governed by the relationship between M2 and its compound tide M4) over the northwest European shelf seas can further affect power generation at potential high-energy sites. Based on these variabilities, the spatial distribution of the tidal-stream ‘capacity factor’ has been calculated. We find that mean peak spring tidal velocities can under-estimate the resource by up to 25%, and that annual practical power generation can vary by ∼15% for regions experiencing similar mean peak spring tidal velocities, due to the influence of other tidal constituents. Therefore, even preliminary resource assessments should be based on annual average power density, rather than peak spring tidal velocity.
Highlights
The tidal-stream renewable energy industry – where the kinetic energy inherent in the oceans is converted into low carbon electricity – is at a crucial stage of development, where single-device tidal-stream energy converters (TECs) have been installed and grid-connected at high-energy sites
Using a three-dimensional hydrodynamic model (ROMS) at $1 km spatial resolution, and applying device characteristics of the Seagen-S turbine, we show that the ratio of the amplitudes of the M2 and S2 tidal currents can lead to significant variability in annual practical power generation – variability that is not accounted for when considering only the mean peak spring tidal velocities, as is generally the case in resource feasibility studies
This paper is structured as follows: Section 2 describes the theory of tidal variability over the northwest European shelf seas; model characteristics and validation are described in Section 3; analysis of the tidal current variability is presented in Section 4, enabling the tidal-stream energy resource to be mapped according to the criteria explained above; our discussions and conclusions (Sections 5 and 6, respectively) are presented in the final sections
Summary
The tidal-stream renewable energy industry – where the kinetic energy inherent in the oceans is converted into low carbon electricity – is at a crucial stage of development, where single-device tidal-stream energy converters (TECs) have been installed and grid-connected at high-energy sites (e.g., www.marineturbines.com; www.openhydro.com). We investigate the spatial and temporal variability of the magnitude of the tidal currents and potential power production across the northwest European shelf seas, with the aim of improving our understanding of the net tidal-stream energy resource and optimising energy yield. A 3D model has been implemented, results are presented on the basis of depth-averaged velocities These waters are some of the most energetic in the world in terms of tidal energy dissipation (i.e., dissipating approximately 10% (0.25 TW) of global tidal energy; [9], and this study will add considerable value to the European marine renewable energy industry in terms of resource assessment and potential optimisation strategies, and our methodology could be applied to other regions of the world with an energetic tidal resource. This paper is structured as follows: Section 2 describes the theory of tidal variability over the northwest European shelf seas; model characteristics and validation are described in Section 3; analysis of the tidal current variability is presented in Section 4, enabling the tidal-stream energy resource to be mapped according to the criteria explained above; our discussions and conclusions (Sections 5 and 6, respectively) are presented in the final sections
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