This paper presents an experimental study on the performance of a reverse electrodialysis (RED) stack for SELEMION, ASTOM, and FUJI membranes with the cell pair number from 3 to 15 and flowrate from 5 to 60 L/h over a wide solution concentration range from 1 to 120 g/L. Direct current and alternate current measurements are employed to identify quantitatively the contribution of ohmic and non-ohmic resistances to the stack total resistance and then, the power output is predicted theoretically. The results show that the ohmic resistance dominates in the stack total resistance and accounts for about 90%. The factors such as the membrane type, cell pair, solution concentration, and flowrate have a considerable impact on the power generation process of RED. Especially, simultaneously increasing the high concentration (HC) and low concentration (LC) solution concentrations is more conducive to suppressing the concentration polarization when compared with increasing HC solution concentration alone. Although the concentration polarization maintains declining with the increase in flowrate, the flowrate should not be too large in order to harvest the highest power output by reason of serious tangential flow at higher flowrates. The optimal performance of RED stack is obtained when SELEMION membranes are used with cell pairs of 5, HC–LC solution concentration of 120-4 g/L and feed flowrate of 20 L/h.