Due to the predictable nature of the tides, power generation from tidal streams could play a significant role in addressing future power network challenges by providing an auxiliary frequency balancing service. A requirement of such services is that power output may be rapidly adapted. This can be achieved by several alternative operating strategies applied to individual turbines, to entire farms or to clusters of turbines within a farm. The onset tidal flow speed to an array is sensitive to the net resistance provided by the array and so it is necessary to consider how such strategies would affect power output, net resistance and the flow onset to the farm. Investigations using a Reynolds-averaged Navier-Stokes Actuator Disc (RANS-AD) model and experiments in a shallow channel are conducted to assess the influence of rotor operating point on individual turbine loading and hence aggregate resistance of an array. Array- and row-specific values for the local thrust coefficient and corresponding disc porosities are chosen to represent three typical operating values of turbine thrust and power.
Both studies are assessed separately for turbine array configurations with up to 12 turbines deployed over 3 rows and in bi-directional flow. The results show good agreement with previous experimental and numerical publications. Additionally, similar trends are observed for the variation of the net array thrust coefficient with array layout and operating point for both studies.
Application of these array operating points within a simple channel model indicates that the imposed net thrust can be reduced by 12.3% whilst the energy yield reduction over a 12 hour period is almost negligible.
Thus, an adaptive operating strategy does not only provide more accurate information of the power output from tidal farms and reduces the environmental footprint of the latter, but also promotes a more flexible array operation which can facilitate a better grid integration of future large-scale tidal stream turbine arrays.