Kinetic hydropower involves the use of hydro turbines, submerged within existing currents for power generation. They are applicable to ocean and tidal currents, rivers, and human-made channels. This versatility gives them advantages over conventional hydropower, however they suffer from low power densities. This numerical study investigates the use of diffusers to enhance the performance and viability of kinetic hydro, turbines. To simplify the problem, the turbine is modeled as a momentum source region, a strategy that is first validated against Betz theory. The diffuser configuration produces 3.1 times more power than the turbine with no diffuser. A scaling analysis also shows a turbine with a diffuser outperforms a larger size turbine with no diffuser. (C) 2009 Elsevier Ltd. All rights reserved.