when you dissolve salt in water, then salt splits into ions and each can hold up specific number of water molecules, which means that this water can’t do water things. so on top of salt’s physical presence, there’s a fraction of water that can’t water, or salt water is less watery in a sense than fresh water. now it turns out, if you put a membrane between these two that allows water through but not salt, water goes to higher salinity on its own, because there’s less watery there. how hard it happens is quantified as osmotic pressure and it can be in tens of atmospheres. reverse electrodialysis is just a clever arrangement that avoids energy recovery from low volume of high pressure liquid, like how reverse of reverse osmosis would work
Comment on power generator
frank@sopuli.xyz 1 week agoYeah, it’s a super rad tech! A bit pricey but a neat renewable that almost generates opposite to solar in a way, in that if it’s raining you’re getting some energy in the form of fresh water
Can you ELI10 an intuitive explanation on why the salinity gradient provides energy? It doesn’t make intuitive sense to me and never has. Like why is fresh water mixing with salt water energy positive?
rain_enjoyer@sopuli.xyz 1 week ago
marcos@lemmy.world 1 week ago
It doesn’t. It’s the thermal energy that is converted to electricity.
The salinity gradient provides an entropy dump. The dialysis machine is built in a way that the only possible way for that entropy to increase is by generating some electricity.