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This energy originates because of difference in salt concentrations at the junction of river and ocean or sea. Energy generation from salinity gradient is a two‐stage process. The ‘pressure retarded osmosis’ is used where freshwater flows through a semi‐permeable membrane to increase the pressure in a reservoir of seawater and ‘reverse electro dialysis’ with ions of salt passing through alternating reservoirs of sea and river water. Recently, a research estimated the potential of salinity gradient energy as approximately 1650 TWh/yr. (Cornett 2008, p. 9). At present, the major challenge faced by utilization of this energy is its high cost of power generation. In 2009, this energy was harnessed for the first time at Tofte site (Nihous 2010).

Currently, harnessing ocean energy using different technologies is in its infancy due to costly technologies, high capital cost, socio‐economic impact on shipping and tourism and environmental effects. There are several technical issues which are associated with this energy such as device manufacturing, installation, maintenance and grid and power transmission. Further, due to lack of studies which establish the impact of ocean energy exploitation on marine environment, aquatic ecosystem and water pollution due to corrosion of various device obstructs its development.