The Estuary at River Erme. Courtesy FlickrAnother day, another source for alternative energy. This time, scientists are working on harnessing the energy produced by the mixing of fresh and salt water, particularly that which occurs in an estuary. The mixing generates 2.2 kJ of energy per liter of fresh water that flows into the sea.

According to PhysOrg.com:

The EDL 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 only energy required by the system is the initial power source to jumpstart the capacitor, and power to pump fresh and salt water into the device.

Scientists intend to ramp up the scale for industrial use and expect that the costs would rival that of wind power. But head researcher, Doriano Brogioli, sees this method as a complement to wind and solar power, for those areas that may not have access. He states, "In other places, it can be better to use solar energy with a concentration device, for example, or small wind turbines, biofuels, or whatever else, perhaps including fossil fuels or nuclear power. In this sense, my method is an ‘alternative’ to other ‘alternative’ energy sources.”