Millions of litres of water constantly flow into the sea from the world’s rivers yet scientists may have discovered a way of turning it into electricity without using barrages or even turbines.

A report on the New Scientist website states that a gigawatt of electricity could be created (enough to power 650,000 homes) by channeling the salt water of the north sea and the fresh water of the River Rhine through a type of battery.

The idea originates from the invention of the modern desalination plant that turns salt water into fresh water by pumping it through a membrane – a technique known as reverse osmosis.

One of the two inventors, Sidney Loeb, envisaged using the same technique to create pressurized water containing enough energy to power a turbine. Loeb named this process pressure retarded osmosis (PRO) and patented it in 1973.

The technology has been held back by the lack of a suitable membrane that divides the salt from the fresh, yet allows the molecules through when pressurized.

Norwegian scientists are close to developing full working prototypes, claiming global capacity to be 1600-1700 terrawatts – 1% of global capacity.

A competing Dutch technology reckons its similar system could generate as much as 7% of global demand.