Salinity gradient is a non-conventional renewable energy form which is widely available worldwide. Reverse Electrodialysis is a promising and innovative technology able to convert directly this chemical renewable energy into electricity. This paper presents a number of different scenarios where salinity gradients are naturally available or they result from industrial/urban activities. A sophisticated model accounting for all the main phenomena (including all the detrimental ones) occurring within a Reverse Electrodialysis unit has been purposely developed. The model is used to calculate how much electric energy can be harvested from the above-mentioned salinity gradients.