Experimental optimisation of power for large arrays of cross-flow tidal turbines

Abstract As commercial scale tidal energy devices are shortly to be deployed in the first arrays, the knowledge of how different array layouts perform is a key and under-examined field. Here, the Momentum Reversal Lift (MRL) turbine, developed by the University of Exeter, is deployed in five different array layouts utilising up to 15 devices. The use of dynamic turbines allows the inclusion of analysis of the effects of flow direction in the wake. The layouts investigated explore the effect of lateral and stream-wise turbine spacings as well as differences between staggered and in-line layouts on power. The staggered array with decreased streamwise spacing is shown to have the highest total power per ‘footprint’ area among the layouts tested. For the staggered arrays, increased downstream separation had little effect on total power generated, while decreasing the lateral spacing below 2 rotor diameters decreased the power. The in-line arrays showed a lower power per device but similar total power. It was also shown that increased in-flow into a turbine didn't necessarily lead to an increased power extraction. The decrease in power with a decrease in streamwise spacing is in-line with theoretical and CFD predictions.