Going PRO: The Grand Gradient

Courtesy of: Yip and Elimelech 2014

The major untouched source of energy on planet is that of water, but not just water, the salinity gradient it contains. There are two methods that have been studied, Pressure Retarded Osmosis (PRO) and Reserve Electrodialysis (RED), in order to see how the energy efficiency and power density would perform in real simulations. The study found that a higher efficiency (useful work) was more attainable in PRO over RED, due to the fact that frictional loses, resistive loses, uncontrolled mixing loses and unutilized energy in RED overpowered the little useful work it created. PRO also worked better than RED when put through the three types of gradients: natural (seawater - river water), anthropogenic (desalination brine - wastewater effluent), and engineered (synthetic hyper-saline solutions). Power density in this study is defined by the the amount of area the salinity energy has to use, and once again PRO was able to create the most energy using the less amount of area. The outcome of this study shows how energy could be harvested from the many streams and rivers found around the world.

Reference:

Ngai Yin Yip and Menachem Elimelech (2014). Comparison of Energy Efficiency and Power Density in Pressure Retarded Osmosis and Reverse Electrodialysis. Environmental Science & Technology, 48, 11002-11012.