Salinity Gradient

The salinity gradient, or osmotic energy, is one of the emerging renewable energy resources available for countries with access to the sea. Two basic concepts of generating power from salinity gradients are presented: (a) pressure-retarded osmosis (PRO) and (b) reverse electro-dialysis (RED) systems. The advantages and disadvantages of salinity gradient systems are discussed. The basic equation for estimating energy from the salinity gradient is discussed using similar calculations for estimating the energy required for water desalination systems. The sizing of PRO systems is discussed with examples and the use of the most recent net power density output from recently achieved designs. If one is interested in calculating the required membrane area for household applications, an example is also presented. This chapter also discusses specific applications and locations for potential salinity gradient projects. Finally, limitations and factors affecting performance are enumerated, including performance and costs. Simple payback period calculations for salinity gradient facilities are also presented by way of examples from actual pilot plants. There are barriers to the large-scale use of the salinity gradient, and this must be included in the design. Engineers must consider suitability, sustainability, and reliability for widespread adoption.