An array of tidal stream generators situated off Portland Bill headland (English Channel coast, Southern UK) was simulated using a two-dimensional finite element model developed with the TÉLÉMAC hydrodynamic modelling system. The effect of energy extraction was parameterized as a stress proportional to the square of flow speed, linearly interpolated in space across affected elements within the mesh. Different resolution finite element meshes were used to indicate the degree of mesh-independence of the simulation. For each run, one month of simulation results were analyzed in terms of Z harmonic constituents using T_TIDE. The distributions of cubed speeds over 18.6 years were then compared for cases with and without energy extraction, in order to quantify the difference in predicted input power to the generator array. It was found that in the bin that was closest to the rated speed chosen for the array, 15– 16 (m/s)3, there was a reduction in available energy of approximately one third. This implies that there could be a large impact upon individual generator design criteria in this case, subject to future validation of this method of simulating energy extraction, through experimental results.