6. Other Technologies

6.3. Salinity Gradient

The principle behind salinity gradient power (or osmotic power) is that there is a difference in entropy between salt and fresh water which can be exploited for the production of energy. This form of energy is a complex concept as it cannot be detected in the same way as other forms of energy such as solar, wind or wave. However, considering that the reverse process, desalination of seawater, requires large amounts of energy, the principle behind salinity gradient power is more logical1.

There are two methods in development: reverse electro-dialysis (RED) and pressure retarded osmosis (PRO). Both of these processes use alternate chambers separated by semi-permeable membranes. The RED method involves the migration of salt ions, by osmosis, through the semi-permeable membrane, thereby creating a low voltage current2. The PRO method uses a membrane which is more permeable to water than to salt. Water molecules will be forced through the membrane to the salt water side. As water molecules pass through the membrane, hydrostatic pressure will increase on the seawater side, up to a maximum of 26 bars2. This pressurized water is used to drive a turbine and make electricity.

 

References

1. Statkraft, Osmotic Power. [online]: http://www.statkraft.com/Images/Statkraft%20Osmotic%20Power_tcm4-5362.pdf (14 November 2008).

2. UN Atlas of the Oceans, Salinity Energy. [online] http://www.oceansatlas.org/servlet/CDSServlet?status=ND0zMDY0JjY9ZW4mMzM9KiYzNz1rb3M~ (14 November 2008).

llp logoThis project has been funded with support from the European Commission (EU Lifelong Learning Programme Agreement no LLP/LdV/TOI/2009/IRL – 515). This publication reflects the views only of the author, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

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