Reverse Electrodialysis Energy Harvesting System Using High-Gain Step-Up DC/DC Converter

Salinity gradient power (SGP) between fresh river water and sea water is a form of renewable energy with huge potential but not well explored. This paper presents a feasibility study on energy harvesting of SGP based on: 1) the use of reverse electrodialysis (RED) stack, and 2) the combined use of harmonics-boosted resonant inverter and multistage diode-capacitor step-up converter. The properties of an RED stack have been characterized into steady-state ac and dc equivalent circuit models for power converter design for the first time. The gains of the resonant inverter and diode-capacitor step-up converter are also optimized for maximizing the energy efficiency. An RED stack prototype comprising multiple alternating anion and cation exchange membranes with an area of 0.01 m(2) each has been constructed. The dc output voltage of 2-3 V from the RED stack has been stepped up to be over 155 V. This study has confirmed that energy can be harvested with a membrane power density of at least 1.4 W/m(2), a power converter's efficiency exceeding 85%, and a voltage gain of 67.3 times.