Could blue be the new green, asks BBC Future, referring to the so-called blue energy generated when fresh water rivers flow into salt water estuaries:
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It is perhaps one of the most under-exploited sources of green energy. When salt water and fresh water mix in estuaries, a chemical process occurs that can be harnessed for electricity generation.
According to one estimate, this “blue energy” is so plentiful that it could meet all our needs – if we can find an effective way to tap it. Could ‘blue’ be the new green?
Blue energy was first proposed in 1954 by a British engineer named R E Pattle. It is sometimes called “osmotic power”, because it exploits the phenomenon of osmosis. To understand how this works, picture two solutions of water with different concentrations of a dissolved substance like salt. If these two solutions are separated by a thin “semi-permeable” membrane that lets water through but not salt ions, then water will naturally pass from the less- to the more-salty side.