Abstract
Tidal current turbines have the potential to make a considerable contribution to renewable energy supplies. However, the potential for utility-scale deployments will depend not only on the economics of power generation, but also on the likely hydro-environmental effects of deployments. These may include physical, acoustic, chemical, and electromagnetic effects but the effects of energy removal are considered most significant. This paper presents a review of the available published literature on the hydro-environmental effects of energy removal of tidal turbines. Given the limited number of ocean deployments of turbines to date, the relevant literature mostly comprises laboratory studies of singular scaled turbines and CFD model studies of multiple device arrays. The review finds that the hydrodynamic impacts of singular devices are relatively well understood and that it is generally accepted that the far-field effects of singular device deployments, and even small arrays, will be negligible. In contrast, large arrays have the potential to affect much greater changes in their far-field environments with the research showing potential for large reductions in current velocities inside, and upstream and downstream, of the array, and consequential impacts on mixing, mass transport and primary production. The review focused on those studies that attempted to quantify the magnitudes of any energy removal effects. As might be expected, the reported magnitudes of effects varied widely but there is a strong positive correlation with the level of energy removal. Indeed, the literature indicates that for most suitable deployment sites there exists a safe level of energy removal that would be both economical and environmentally sustainable. The authors recommend the application of combined hydrodynamic-biogeochemical models on a site-by-site basis to help determine the significance of any hydrodynamic impacts and therefore the appropriate sustainable levels of energy removal.