Seas and oceans are often seen profitable for their waves’ power, but few know that these huge salt water recipients store energy in yet another way: in their salt. The new approach sees the entire oceans and seas as battery electrolytes. Interesting? Read on.
When a battery charges, electrons are exchanged with ions in a move between the electrolyte and the electrodes. If the classic version of a battery keeps the ions inside, the one described in a recent Nano Letters issue allows the ions to exchange freely with oncoming water.
Saltwater has some salt ions that naturally exist in it, such as manganese dioxide. These ions can react with the carefully-chosen battery electrodes, and can form Na2Mn5O10, a harmless compound having a high energy density. This is basically how the battery charges itself. Saltwater flows between the electrodes, the electrodes react with it, and capture the ions. To release the energy,saltwater has to be replaced by freshwater, and the cycle is reversed.
The battery has been named “mixing enthropy battery,” and the study authors say it’s about 75% efficient. A hundred charge/discharge cycles later, the battery didn’t show any sign of damage.
Huge amounts of energy can be generated by using this type of battery. A water flow of 40 cubic meters per second can generate up to 100 megawatts, while globally there may be a theoretical value of 2 terawatts – much less than the estimated 47 TW worldwide energy consumption, but it’s something (4.2%).
Solar power storing devices have also been envisioned and tested, involving the evaporation of fresh water from a salt stock driven by heat.