Salinity gradient has globally high potential for electric energy production, especially where low salinity rivers discharge into hyper-saline lakes. Lake Urmia is world's second hyper-saline lake, with a number of low salinity rivers discharging into the lake, the most significant of which is ZarrinehRud River. Based on thermodynamic calculations and on field data, the theoretical potential of energy production at the above system has been calculated between 400 and 1000 MW, while the technical potential is expected between 40 and 50% of that. Two processes for the production of electricity from salinity gradients were investigated: PRO and RED. The revenue of such attempt is a function of membrane cost, power density, lifetime expectation and sale price of electric power. Based on the available technology, the project is expected to be viable if membranes with power density above 5 W/m(2) and 10 years lifetime expectancy or 10 W/m(2) and 5 years lifetime expectancy will be used. The cost of membranes for a 25 MW plant has been estimated between 75 and 150 million USD, while the cost of electric energy from a full-scale PRO plant is expected to be between 65 and 130 USD/MWh (comparable with the cost of electric energy generated from other renewable energy sources). (C) 2015 Elsevier Ltd. All rights reserved.