![]() ![]() 11Ī tidal range power plant is based on a number of components, the most important of which is the embankment. It is generally considered that the next generation of tidal range power plants will be lagoons, which only partially span an estuary, since these are associated with lower capital cost and reduced environmental impacts. Further, all of the existing tidal range power plants are of the barrage type that is, they span the full width of an estuary or channel. Four other tidal range power plants have been constructed ( Table II), but it is notable that no scheme has been constructed in the last 25 years, setting aside the complication that the embankment for the 254 MW Lake Sihwa barrage was constructed in 1994, and the power plant in 2011. The barrage houses 24 Kaplan bulb turbines, which provide a combined rated power output of 240 MW. 10 La Rance comprises a 720-m-long barrage and impounds an area of approximately 22 km 2 in a region that has a mean tidal range of around 8 m. 9 However, converting the potential energy of the tides into electricity began with the construction of La Rance power station (France) in 1966. 5Ĭonverting tidal range into other useful forms of energy has a history that extends back to the tide mills of the 6th Century. At longer timescales, the tidal resource is also influenced by the effect of the 18.6-year lunar cycle, which is mainly driven by the changes of the inclination of the Moon's orbital path relative to the plane of the Earth's equator. In addition to M2 and S2, other important tidal constituents that significantly affect the temporal variability of the tides are the lunar (O1) and lunisolar (K1) diurnal constituents, and the larger lunar elliptic semi-diurnal constituent (N2) ( Table I). It can therefore be seen that there is variability of the tides (and hence the potential of the tides for electricity generation) at both semi-diurnal and fortnightly time scales ( Fig. The combination of M2 and S2 leads to the fortnightly spring-neap cycle, with enhanced tidal range (spring tide) when the Earth–Moon–Sun system is in-line (either New Moon or Full Moon) and reduced tidal range (neap tide) when the Earth–Moon–Sun system is perpendicular (either First Quarter or Third Quarter Moon). These manifest as a number of tidal constituents, the dominant of which are the semi-diurnal lunar (M2) and solar (S2) constituents, with periods of 12.42 and 12 h, respectively ( Table I). Tides are predictable because of their origin in (astronomical) tide generating forces. 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. 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). 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. 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. 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. 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. ![]() Here, we review both tidal range and tidal stream energy, with a focus on the resource, feedbacks, and environmental interactions. The ocean contains a variety of renewable energy resources, little of which has been exploited. ![]()
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