Salinity Gradient Energy Conversion

The feasibility of Osmo-Hydro Power^TM(OHP) systems, as conceived by ITC/Solar, to generate electricity in a practical and economic manner from aqueous saline solutions is discussed. Initial design of a 50-kWe system using brackish water and saturated brine is presented. Preliminary estimates show that for larger units the capital cost of such a system will be around $4,000 to $5,000 per net kWe. The technical and economic feasibility of salinity gradient energy conversion using Osmo-Hydro Power^TM(OHP) systems was investigated by InterTechnology/ Solar Corporation (ITC/Solar) under two Department of Energy funded projects. Under one project (1) laboratory experiments were done to investigate several technological problems of such a system, including membrane compaction under high hydraulic pressures, salt polarization, and brine-induced deterioration of membranes. The second project (2) was concerned with the development of OHP systems for utilizing various sources of salt and water, development of a system simulation model, and assessment of the potential for salt/water OHP systems to generate power in the U.S. Under this project, preliminary performance estimates were made with a comprehensive model for OHP systems. Results of these two projects are well documented in References (3) to (6). This paper will discuss some of the pertinent results from these two projects. Encouraged by the findings of these two studies, the Department of Energy awarded a joint contract to Ebasco and InterTechnology/Solar to design a 50-kW system, which started in January 1979. The first phase of this contract was completed in April 1979 (7). The results of this phase are also discussed in this paper. In particular it will be shown that Osmo-Hydro Power systems utilizing seawater or brackish water are feasible. Furthermore, with the development of pressure-retarded osmosis membranes, these systems could be cost-competitive with other renewable energy systems.