Researchers cast doubt on economics of osmotic power

New research findings have questioned the economics of power production from pressure retarded osmosis (PRO).

A team from Yale University in the US shows that a typical constant pressure PRO would find it challenging to generate a sizeable amount of energy. PRO exploits a salinity gradient between two water sources – typically using seawater as the draw solution and river water as feed solution.

The Yale paper theoretically evaluates membrane modules employing co-current and counter-current flows with different salinity source waters to determine the maximum extractable energy that will establish PRO’s viability.

According to the researchers doubts over PRO’s economics grow further on considering efficiency losses from reverse draw flux, external concentration polarization, membrane fouling and pretreatment energy requirements.

In December last year Norwegian state-controlled power firm Stadtkraft abandoned its development of PRO – sometimes dubbed osmotic power – after years of research and announcing plans for a large demonstration plant in Norway. Norway was seen as having an ideal combination of freshwater fjords and seawater coastlines for the exploitation PRO.

PRO – sometimes dubbed osmotic power – is a membrane process that combines aspects of forward osmosis (FO) and reverse osmosis (RO) to convert seawater’s natural osmotic pressure into hydrostatic pressure that can be used to drive a turbine to produce electrical energy. The concept was initially developed and patented by Sidney Loeb, the co-inventor of the RO membrane, in 1973.