Numerical model simulations for optimisation of tidal lagoon schemes

Abstract

This study considers environmental impacts and the power production potential of a number of coastally attached tidal lagoons, proposed along the North Wales coast, UK. Initially, the impoundment shape, turbine and sluice gate locations were modified according to the regional bathymetric data. A refined 0-Dimensional approach was implemented to optimise the lagoon operation, based on given turbine and sluice gate specifications. In turn, a two-dimensional numerical model, based on an unstructured triangular mesh, has been refined to simulate the hydrodynamic processes, initially without and subsequently in the presence of the lagoons. The hydrodynamic model adopts a TVD finite volume method to solve the 2D shallow water equations, based on a second-order accurate spatial and temporal numerical scheme. An encouraging performance is apparent in reproducing the established conditions encountered in the region through comparisons against available data. The incorporation of tidal lagoons in the model appears to have a considerable effect on the flow structure in the region, by inducing high velocity accelerations near the sluices and turbines, depending on the stage of the tidal cycle. Considering a two-way generation regime, it is outlined that the loss of intertidal regions can be minimised, which is a major source of concern with regards to the environmental impact of such schemes through an ebb-generation operation. Particular focus is directed towards the comparisons between the 0-D and 2-D modelling results, an aspect which has not been reported previously. Predictions of the models diverge as the scale of the lagoon project increases, but it is highlighted that the 0-D methodology can be utilised for the optimisation of the processes in the initial stages of design before proceeding to more sophisticated numerical model simulations

Optimising tidal range power plant operation

“…The drawback of 0-D models in neglecting the impact of tidal power plants on local and regional hydrodynamics can be significant for larger tidal lagoons and barrages [5,29]. To address this, regional coastal ocean models can be used to predict the flow elevations, velocities and the altered tide constituents.…”

Comparison of 0-D, 1-D and 2-D model capabilities for tidal range energy resource assessments

“…[4]. While the particular domain is insufficient to rigorously assess the hydrodynamic impacts of a Severn Barrage, the power predicted at the site is independent of the far-field effects downstream and was therefore not extended for simplicity [11] with the interested reader directed to associated studies [30].…”

“…turbines and sluice gates), it is possible to simulate the performance of a tidal range structure [11], [12]. The plant operation can be modelled using a water level time series representing the transient downstream water elevations at the site location [3], [13], [14].…”

“…In the classical study of [9], it was assumed that (i) the flow through the turbines is at a constant flow rate Q and that (ii) power generation starts and stops at the same prescribed minimum head h min . Since then, developments in 0-D modelling for tidal range structures have been presented by [11], [13]- [15] so that:…”

“…Examples of 0-D modelling include successful applications to optimise plant operation parameters [11], estimate the energy output of proposed tidal range structures [16], and assess certain hydro-environmental interactions such as the effect of storm surges on the energy output of tidal range turbines [17].…”