Fire from Water - Alternative Energy from the World's Most Plentiful Resource

One of the primary challenges faced by the world today is human civilization’s seemingly insatiable demand for energy. Access to stable, abundant and reliable forms of fuel has taken its place alongside the importance of food, clean water, health and human rights in the 21st century.

In all likelihood, the energy of the future will be produced using a variety of methods. One promising production technique was proposed by scientists at Stanford University in a recent American Chemical Society (ACS) journal of Nano Letters.

The novel concept would utilize estuaries where fresh water and sea water mix as potential sites for power plants. So-called entropy batteries would charge off the difference in the salt content of the sea water and fresh water, providing clean power in a reasonably safe and secure way.    

It’s long been known that electricity can be generated by differing saline content in water but up until now, the methods have been too costly and impractical for large-scale energy production.

The new battery is built around a fairly simple premise. Two electrodes – one containing positive sodium ions and one containing negative chlorine ions – are immersed in the fresh river water of a site like Belem, Brazil, where the Amazon ends its 6,400 kilometre trek to the Atlantic Ocean. 

A small electrical charge is applied to the fresh water, which pulls ions from the electrodes and slowly charges the battery. Then the water is drained and replaced with salty sea water, which contains 60 to 100 times more ions than fresh water.

As a result, the electrical potential – or voltage – between the two electrodes is dramatically heightened, causing a significant net energy gain over the amount used to charge the battery. 

“If you charge at low voltage in fresh water, then discharge at high voltage in sea water, that means you gain energy,” said Stanford University researcher Yi Cui. “You get more energy than you put in.”    

Although the practical, large-scale operation of such an approach is still years away, scientists believe their plan could potentially supply about 13 percent of the world’s energy needs. 

According to statistics from British Petroleum, total worldwide energy consumption was 474 exajoules in 2008, the equivalent of an average annual power consumption rate of 15 terawatts.

If these numbers are accurate, the entropy battery could produce roughly 60 exajoules globally, provided all the world’s rivers were harvested in such a way. 

However, this seems unlikely – at least in the near future - since a variety of competing interests are likely to deter the implementation of any new form of large-scale energy production, no matter how promising or cost-effective its methodology may be.