Hydro-environmental Modelling of the Impacts of Turbine Layout and Design Considerations of Tidal Range Schemes

Introduction

Modelling potential sites for tidal range energy across the world Neill et al, (2018) estimate a theoretical annual output of 25,880 TWh across 11 countries. The predictability, availability and sustainability of tidal range energy makes it an ideal alternative to fossil fuels for producing baseload power whilst boosting the marine energy industry. Despite the presence of this plentiful resource across many countries, the development of Tidal Range Structures (TRSs) has so far been limited to a handful of locations globally due to technical, financial and environmental concerns. The environmental impacts of TRSs must be addressed in order for this technology to be actualised.

Method

Whilst most research into TRSs deploys numerical modelling, this research adds to the body of knowledge using physical modelling to investigate the hydro-environmental impacts of varying TRS designs. A 1:5000 scale model was built in the Hydro-environmental Research Centre at Cardiff University to test the effects of varying turbine spacing in TRS seawalls as well as comparing the impact of different shaped TRSs with the same area. Acoustic Doppler Current Profilers were used to record velocity, whilst water level data was obtained using pressure cells and fluorescent dye was injected into the TRS and filmed in order to visualise flow.

Results

Results showed that velocity patterns are most influenced by turbine spacing and that tight spacing leads to the greatest impact on baseline conditions due to concentrated wake effects. Wider spacing promotes slower circulation which would enable other activities to take place within TRSs but may lead to issues with water quality if flows are too slow to facilitate effective flushing. Both square and rectangular TRS designs showed similar results within the TRS but a rectangular TRS leads to greater blockage effects outside. This emphasises the need for site specific design to take coastal conditions into account. Overall, turbine spacing has a greater impact on flow conditions than the number of turbines, and central placement with wider spacing was found to be best for maintaining natural conditions.

Acknowledgments

This research is funded as part of the Water Informatics Science and Engineering Centre for Doctoral Training under a grant from the Engineering and Physical Sciences Research Council, grant number EP/L016214/1.

References

Neill, et al. (2018) Tidal range energy resource and optimization – Past perspectives and future challenges. Renewable Energy, 127, 763-778.