Global energy production is shifting towards more distributed technologies, where power generation takes place close to people. A vaned Savonius wind turbine is one of the possible solutions, which can fulfil the requirements of being simultaneously reliable, safe and non-disturbing. One challenge is that when the size of the turbine becomes smaller and the wind velocity is low, the Reynolds number effects begin to deteriorate the performance. Public literature lacks detailed information about how the turbine performance and internal flows change in these conditions. In this work, a vaned Savonius turbine is tested in a wind tunnel with seven Reynolds numbers and several tip-to-speed ratios. The measurements include both the turbine performance and the static pressures inside the vane passages. All experiments are also conducted separately for the stator only configuration to evaluate the effects of stator-rotor interaction. The main results are: (1) a new Reynolds number-dependent performance prediction correlation is developed with an achievable accuracy of +/- 5%, (2) Savonius turbine power coefficient follows the trend of kinetic compressors relatively well and due to the changing Reynolds number, an over 20% drop in vaned turbine performance can be observed, (3) the Reynolds number affects performance through friction and flow separations, but the vane passage pressure distributions are not affected and (4) tip-to-speed ratio affects the vane passage pressure distribution via stator-rotor interaction. It is also suggested that the nominal tip-to-speed ratio should be kept relatively low in the design phase to minimise the negative effects of stator-rotor interaction.