Abstract
A one-dimensional head driven channel flow model is used to investigate the characteristics of tidal stream energy extraction for large tidal farms deployed in tidal channels with specific focus on the limitations to realizable farm power due to turbine support structure drag and constraints on volume flow rate reduction. Support structures are seen to contribute significantly to the overall resistive force in the channel and thus reduce the overall flow rates through the channel leading to losses in realizable power. Over a wide range of channel characteristics, realistic levels of support structure drag are shown to lead to up to a 40% reduction in realizable power, and an associated reduction in the number of turbines that can be installed. Constraining the permissible flow rate reduction to 10% renders the structural drag to be even more important, reducing realizable power by up to 70% relative to the case without support structure drag and by over 80% relative to the case with no constraints on flow rate reduction and no support structure drag. For realistic levels of structural drag and permissible flow rate reduction, farm power output is seen to be approximately linear in undisturbed peak channel flow speed (or tidal amplitude), as opposed to the quadratic behaviour observed for channels with no constraint on flow rate reduction and no structural drag.