Reverse Electrodialysis

Reverse electrodialysis (RED) is the salinity gradient energy derived from the difference in the salt content between river water and saltwater. At the Ben-Gurion University of the Negev in 1977, Professor Sidney Loeb developed a way to use the energy generated by this process using a heat engine. —U.S. Patent US4171409. In reverse electrodialysis, salt solution and fresh water are passed through a stack of alternating cation and anion exchange membranes. Each membrane experiences a voltage as a result of the chemical potential difference between salt and fresh water; the system's overall potential is the sum of these voltages. The technique relies on a difference in ion concentration rather than an electric field, which has consequences.