Comparative mechanical efficiency of several plant configurations using a pressure-retarded osmosis energy converter

Mechanical efficiencies have been compared for several plant configurations utilizing a pressure-retarded osmosis (PRO) energy converter. In this comparison reliance has been placed on previously obtained experimental data of Honda in a reasonably sized PRO module with hollow fibers sized for PRO use. These data were obtained with a 3.5 percent NaCl solution, i.e. one fairly close to sea water. The comparisons indicate that the continuous flow, terrestrial PRO plant will be too low in efficiency to be effective. The continuous flow, underground PRO plant will be much more efficient but requires that most of the equipment be located in an underground cavern at a depth of about 90 meters below the surface of the sea. The alternating flow, terrestrial PRO plant has high efficiency, but requires the use of two pressure vessels in addition to the usual PRO equipment.