Tidal Range

Abstract

Abstract The idea of extracting significant, utility‐scale energy from the difference in sea level height between high and low tides (the tidal range) has been actively considered for around a century. As well as being a low carbon technology, the scale of the resource is significant, particularly for certain countries, such as the United Kingdom, France, Canada, and Korea. However, tidal range power schemes also present complex challenges, most notably the economics and (particularly more recently) environmental aspects, which are connected. The economics of tidal power schemes is very strongly dependent on the discount rate applied to the cost of energy (CoE) calculation because of the long construction period and the very long life of the main structure, which may represent ca. 50% of the overall costs. Historically, ebb generation has been focused on, as this was expected to have the lowest CoE. However, effective ebb generation, optimized for CoE, generally means that the tidal range within the impounded basin is around 50% of the natural tidal range, and one of the key issues is quantifying the loss of intertidal habitat and its relative impacts, as well as how compensatory habitats could be created. More recently, dual mode generation has been focused on as a means to reduce some of the undesirable environmental impacts of ebb generation, as the tidal range more closely matches the natural tidal range; in addition, the power output may be smoother and therefore easier to absorb onto the grid. As tidal range schemes must have a reasonably significant effect on the natural tidal cycle in order to extract useful energy, mathematical modeling of the tides and associated aspects is required to allow an understanding of both the operation of the tidal range scheme, especially its energy output, and its impacts on aspects such as water levels, currents, sedimentation, and water quality. Although various tidal range schemes have been under development for around a century, only two significant utility‐scale schemes have been built, both being ca. 250 MW . The La Rance barrage in France has been operating for ca. 50 years, and the technology has been well proven. Few significant tidal range schemes are under active development outside the United Kingdom and South Korea; and the United Kingdom's Swansea Bay lagoon scheme in particular may determine the success of the sector in France, the United Kingdom, and Canada over the next few decades. This project attempts to address some of the key economic and environmental constraints that have hampered the sector.