Salinity difference energy also called Blue energy in The Netherlands, is the energy that can be gained by mixing two kinds of water with different salinity. The idea is formulated first in 1954 by R. Pattle in Nature . Mixing 1 m3 of fresh river water with a large amount of sea water gives a mixing energy of 2 MJ. If one would like to extract the same amount of energy from fresh water via conventional hydropower one would need a dam with a height difference of 200 m.
The power available globally in form of salinity difference has been estimated in the 1970s (based on average ocean salinity and annual global river discharges) to be around 2 TW [2, 3]. Thus, in terms of available power, the flow of all fresh water streams combined has the potential to satisfy the current global electricity demand (~2 TW).
The extraction of energy from salinity difference is not limited to the use of fresh
water from rivers. In desert-like regions, it is possible to use the salinity difference
between sea water and a more concentrated salt solution, obtained from sea water through evaporation ponds.
In principle this type of energy generation is inherently clean as this process is based on mixing, a process that happens anyway where the rivers flow out into the seas and oceans. There is no exhaust of CO2 or other polluting combustion emission, while no thermal pollution will occur. This energy source is renewable as it is based on the hydrological cycle powered by the sun. However the technology to economically harvest this energy has not been developed yet.
Here we propose capacitive mixing as a novel principle for electricity generation from the mixing process. The principal advantage of this technology is that the electricity generation is directly linked to the mixing process, while no additional intermediate conversions are necessary. There is thus no need for expensive complex converters like turbines or electrochemical reactions. Therefore this technology holds a great promise to become an economical and environmental benign energy resource, available throughout large parts the world.
1 R. E. Pattle, Nature 174, 660 (1954).
2 R. S. Norman, Science 186, 350 (1974).
3 S. Loeb, R. S. Norman, Science 189, 654 (1975).