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. The flow of water across the membrane builds up pressure on one side that can be used to drive turbines and generate power.

It wasn’t possible to exploit Pattle’s idea for power generation until the 1970s. That’s when artificial materials for making semi-permeable membranes became commercially available. An […]