Tidal stream technology is a promising source of renewable energy which is expected to contribute to the global energy mix by 2050. The technology is currently still in its infancy and the road to commercialisation relies on extensive research and development that will improve the operability of tidal devices and increase the efficiency of power generation. This report presents the results of an experimental study into the performance of scale model horizontal axis tidal stream turbines placed in different array configurations.Optimising an array configuration can maximise power extraction which is essential in driving reductions in the levelised cost of energy associated with tidal power. In the experimental investigation presented, three scale model turbines were placed in four different configurations. The flow data and turbine performance data were analysed to determine which array generated the most favourable results. The four array layouts were all setup with two upstream devices with a single downstream device. These devices were set in a delta shape with tests repeated with differing lateral separation between upstream devices and longitudinal separation between the front row and the single downstream device. A single array configuration with the downstream device 7.8D downstream of the front row of turbines was tested along with three compact array cases with the downstream device was set at 3.2D downstream of the front row of devices. All three devices were operated at a constant rotational speed for a given test and array configuration as facilitated by the permanent magnet synchronous machine operating under servo control. To achieve a range of operating conditions for each array configuration, a range of experiments were undertaken at each layout with the downstream device operating at differing rotational velocities.