Two electrodes, stacked one on top of the other. Image credit: Doriano Brogioli.
Now That's a Clever Source of Power!
When you mix fresh water with salt water, a reaction happens so that a new salinity equilibrium can be reached. This dissipates energy that could be harnessed and turned into clean electricity using a new technique developed by Doriano Brogioli of the University of Milan Bicocca in Monza, Italy. Are we about to enter the era of "estuary power"?
Here's how it works:
The [electric double layer] capacitor is made of two porous carbon electrodes immersed in salt water. The electrodes are then connected to a power supply so that one becomes negatively charged and the other positively charged. Since salt water consists of positively charged sodium ions and negatively charged chloride ions, the positive electrode attracts the chloride ions and the negative electrode attracts the sodium ions. With the help of the electrostatic force keeping the oppositely charged ions near their respective electrodes, the EDL capacitor can store a charge.
To extract the charge, fresh water is pumped into the device, causing the sodium and chloride ions to diffuse away from the electrodes against the electrostatic force. In other words, the work done by the fresh water to extract the salt water is converted into electrostatic energy, appearing as an increase in voltage between the electrodes. Overall, the system transforms mechanical work (the mixing of the salt and fresh water) into electrostatic energy that can be extracted as usable power.
The beauty of this is that the world has plenty of estuaries, and if this technology can be scaled up, it has the potential to produce many gigawatts of "always on" clean power, the holy grail of renewable energy.
Of course this is still in the lab, so there are still a lot of unknowns that need to be figured out before a real world deployment could be possible (and even if it's technically possible, cost will be an important factor), but it's definitely worth keeping an eye on this technology.
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