Draining with Osmosis

For a change I am writing this about a non-railroad issue. It is the English translation of the German article Entwässerung mit Osmose.

Osmosis is described quite well in Wikipedia. In short, mixing of salt solutions with different concentrations sets free some energy. For example when mixing fresh water with sea water, this energy is equivalent to a falling height of 270 m (not 2.8!!!). By using a semi-permeable membrane between the two salt solutions, water molecules will diffuse through the membrane until the sea water side is about 270 m higher than the fresh water side, if dilution of sea water during this process is neglected.

About 30 years ago I have heard about the idea of building osmotic power plants at the mouths of rivers to the sea. They seem to have built a prototype of this recently in Norway and intend to produce 10% of the electricity demand of Norway by osmotic power. This indicates that the concept might become mature soon, even though few countries have as much precipation per inhabitant as Norway, so the achievable percentage will be much lower in most countries.

Another interesting use case of this technology could be draining land areas that are below sea level, like part of the Netherlands or New Orleans. I am sure that there are more of these. Today draining is mostly done by using electric pumps, which consume quite a significant amount of energy. As long as the height difference against the lower tide is less than 270 meters, draining could actually be achieved by using some kind of osmotic pumps without using electricity. Since the height difference is less, it would even be possible to produce some surplus electricity.

I expect that we will see this implemented in areas where applicable within the next ten years, since the osmotic power plant shows that the technology needed for this is becoming mature.

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