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Can anyone explain why the fresh water is needed? The article mentions that the ions in water are not bound to one another so why can’t we just use salt water e

• mnw21cam 7y ago
  There has to be a difference in the water on either side of the membrane. The energy is being extracted from the entropy of the system. Currently, fresh water flows into the ocean, where it mixes with salty water, and goes from a highly ordered system (separate fresh and salty) to a disordered system. We generate energy from heat the same way. It is no good to just have heat. To generate electricity or motion, you also need cold. It is the transfer of heat from hot to cold, making the hot cooler and the cold warmer, that allows us to make use of it. Practically speaking, this membrane lets positive ions through, but not negative ones. So, you put fresh water on one side, which has few ions, and salty water on the other side, which has plenty of both. Then, the positive ions flow through, and you end up with water full of positive ions on one side and water full of negative ions on the other side. That is electricity that can be directly tapped.