Abstract
The tidal stream energy sector is now at the stage of deploying the world's first pre-commercial arrays of multiple turbines. It is time to study the environmental effects of much larger full-size arrays, to scale and site them appropriately. A theoretical array of tidal stream turbines was designed for the Pentland Firth (UK), a strait between Scotland and the Orkney Islands, which has very fast tidal currents. The practical power resource of a large array spanning the Pentland Firth was estimated to be 1.64 GW on average. The ocean response to this amount of energy extraction was simulated by an unstructured grid three-dimensional FVCOM (Finite Volume Community Ocean Model) and analysed on both short-term and seasonal timescales. Tidal elevation mainly increases upstream of the tidal array, while a decrease is observed downstream, along the UK east coast. Tidal and residual flows are also affected: they can slow down due to the turbines action or speed up due to flow diversion and blockage processes, on both a local and regional scale. The strongest signal in tidal velocities is an overall reduction, which can in turn decrease the energy of tidal mixing and perturb the seasonal stratification on the NW European Shelf.
Highlights
The ocean can be a source of energy: from waves, tides, ocean currents, salinity and thermal gradients [1,2]
From a 30-day Scottish Shelf Model (SSM) model run forced by the M2 constituent, the theoretical resource is here defined as the power calculated from eq (6) with CT 1⁄4 1, i.e. all the kinetic energy from the flow is transferred to the tidal turbines
For the specific Pentland Firth tidal array scenario described in this work, considering just the M2 tidal forcing and without including the momentum sink due to tidal energy extraction, the average practical resource is 2.32 GW
Summary
The ocean can be a source of energy: from waves, tides, ocean currents, salinity and thermal gradients [1,2]. Tidal energy has two components, the potential energy due to the sea level variations (tidal range), and the kinetic energy of the tidal currents. Potential energy can be exploited using tidal barrages or tidal lagoons to create sea water level differences, while kinetic energy of the fluid movement generated by tidal currents can be extracted using a suitable underwater type of turbine rotor. Being called “tidal stream turbines”, it has to be noted that a turbine placed in the ocean extracts energy from the total incoming ocean current, which is composed of wind driven and density driven currents, as well as tidal currents
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