The paper treats a new source of energy - salinity gradient which at equilibrium mixing of solutions this energy can be transformed into useful forms of energy, estimates salinity gradient energy sources by the example of Primorye rivers, and treats several methods of salinity gradient energy transformation, first of all including reverse electrodialysis.
Oceans contain a huge volume of a natural solution, such as sea water. Solutions of different concentration have different chemical potentials, useful energy can be received at equilibrium mixture of solutions. Fresh water of the rivers running into the seas and artificial brines of high concentration can to be used as second solution. Such energy sources have received the name - salinity gradients energy (SGE) sources. Salinity gradients have advantages before many other alternative energy sources in size of energy potential and energy density. SGE conversion and usage have minimum environmental influence compared to other energy sources.
SGE resources of several Primorye, Russia rivers are evaluated in the laboratory of non-conventional energetics (Knyazhev, 2008) (Table 1, Fig.1). Summary power potential is 1.5·106 kW in the mouths of rivers of Primorye falling into the Japan sea.
Solutions of various concentrations are characterized by different chemical potentials, as known from chemical thermodynamics; the useful energy can be obtained during the equilibrium mixing of solutions. That is why most methods of conversion for salinity gradient energy are reverse to methods of solution freshening. Molecule exchange of the solvent or dissolved matter between solutions may proceed through membranes, a surface of the intermediate body or surfaces of different phase state solutions.
The reverse electrodialysis is the most promising with exploitation of the SGE source of the type river water-sea water.