Reverse Electrodialyis Salinity Gradient Power Experiment

Today’s rate of fossil fuel consumption rapidly depletes fuel reserves and leads to a number of adverse environmental effects. Although the scope of these effects has yet to be fully realized, it is clear that the development of alternative energy sources is very important. A relatively new form of alternative energy known as reverse electrodialysis (RED) appears to be one of the promising energy sources of the future. This technology harvests the energy stored in the salinity gradient between two different liquids, and converts it directly into electric power. This power is generated by pumping water through an array of alternating pairs of cation and anion exchange membranes called cells. Various academic sources calculate the available energy to be 1.5 MJ for every cubic meter of sea and river water mixed, making all river basins a potential location for power production. Small prototype systems using 50 cells with areas of 100 cm2 were assembled by a group in the Netherlands, but larger stacks remain to be tested. An understanding of the feasibility of RED as a possible energy source relies on testing of cells with larger membrane area and different numbers of membrane pairs. An experimental system was designed with cells 61 cm × 16.5 cm, which will increase the output by nearly a factor of 10. Along with having much larger dimensions than previous systems, the design has an adjustable number of cells in the stack, allowing users obtain test results at a variety of settings. Comparing the output of systems with few cells to systems with many cells will help us to optimize the stack size in terms of hydrodynamic losses. Initial testing of the system resulted in a positive result. The tests showed that the system produced power, and the 1.98 volts measured was 83% of the predicted value. Leakage of the electrode rinse solution contaminated the membranes, and prevented more testing. Once the electrode rinse system is redesigned, more testing will be done.