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‘Two-faced’ membrane can create electricity from salty and fresh water
- Jarmsy 8y ago*nothing but salty water... and fresh water. Pretty important distinction
- taneq 8y agoAmazing new steam engine creates power from nothing but water![1] Still a pretty cool thing if they can just install these in a river mouth and get free electricity out of 'em. [1] And an external heat source such as a coal fire.
- agumonkey 8y agoMaybe even a sea/river buffer dam. Hydro + Osmotic
- kurthr 8y agoYes, it's the fresh water that's rare, and becomes salty in the process so it's sort of like stored solar energy from rain (mostly from the oceans)... osmotic power. https://en.wikipedia.org/wiki/Osmotic_power https://en.wikipedia.org/wiki/Osmotic_power The power density even at 40% efficiency is pretty high (300Wh/m3) so major rivers (Mississippi 20,000m3/sec or 72Mm3/hr) would generate 20GW fully exploited. The problem has always been the growth of biofilms on the surfaces of the membrane, which break them down and/or lower their efficiency.
- jasonmccay 8y agoInteresting ... curious what the replacement cost of these membranes are as compared to installation and ongoing maintenance of wind turbines. Also, as always, curious how having these membranes in the water would affect the local ecosystem.
- mycall 8y agoHave robots constantly cleaning surfaces. Then humans clean the robots.
- kibwen 8y agoThen use the salty water to clean the humans. The circle of life!
- chongli 8y ago20GW is basically nothing next to the environmental damage it would cause by destroying the Mississippi delta in order to build this plant. 20GW gives you 480,000 MWh/d. The US as a whole is currently using over 13,000,000 MWh/d [1]. There is only one Mississippi! Not worth it, if you ask me. Besides, it's not just biofilms that are the problem. With a river you're going to have huge amounts of silt and very fine clay clogging up your membrane. The maintenance costs for an installation like this would be overwhelming. [1] https://www.eia.gov/realtime_grid/#/summary/demand?end=20160802&start=20160702 https://www.eia.gov/realtime_grid/#/summary/demand?end=20160...
- Retric 8y agoThere is far more than just one US river. Hudson for example is: 21,400 ft³/s, Potomac is 10,810 ft³/s etc. And the output is just mild salinity water, so you could probably extract form 1/2 the flow without causing that much environmental harm as long as you pipe the output to an area with similar salinity.
- ambrop7 8y agoIndeed, I assume it has something to do with the second law of thermodynamics. Just like you can't make electricity out of heat alone but need a temperature difference, here you need different concentrations of salt.
- _Microft 8y agoIf you want to read about some interesting stuff, you might wanna research "flux coupling". That is when one flux is used to pump another against a gradient, i.e. in the opposite direction as it would normally flow. That's pretty common in biological systems but there are physical cases as well when e.g. thermal and electric fluxes are coupled (Seebeck-/Peltier-effect).
- stochastic_monk 8y agoThis reaction is also commonly demonstrated in handheld heat pouches and military MRE heating packs.
- callalex 8y agoNo that’s different. That is caused by superheating the salt/water mixture.
- dang 8y agoOk, we'll add fresh water to the title above.
- robg 8y agoUseful any where near a coast where fresh water costs less than electricity.
- ph0rque 8y agoI wonder if this can be reversed to use electricity to make fresh water. Then you can have a giant battery in the ocean that also produces fresh water as needed!
- imhoguy 8y agoThere is no free lunch. Efficiency kills the idea. However the nature sorted it out already - evaporation, clouds, rains.
- perlgeek 8y agoThe reverse process is called desalination, and there are a few approaches to desalination that use membranes: https://en.wikipedia.org/wiki/Desalination https://en.wikipedia.org/wiki/Desalination Typically, you don't use electricity directly, but pump in salt water with high pressure, and some of the water is pushed through, while the salt remains.
- WJW 8y agoThat exists and is called reverse osmosis desalination. https://en.wikipedia.org/wiki/Desalination#Reverse_osmosis https://en.wikipedia.org/wiki/Desalination#Reverse_osmosis
- _Microft 8y agoIf the membrane performs as well in “the wild,” the new membranes could be used to power remote communities with no other sources of renewable energy in just a few years, the researchers say. I wonder what communities they have in mind where neither wind turbines nor solar power are viable options but fresh and salt water are abundant.
- _Microft 8y agoThey only compare it with conventional hydroelectric power in the video (around the 1:50 minute mark) by the way.
- Pxtl 8y agoNorthern Canada? Lacks the transportatjon for the massive weight of the concrete needed for wind, lacks the sunlight for solar. Has fresh water... But question is how much of that water is flowing in winter. I assume this thing fails at sub zero temperatures.
- danans 8y agoWhat,if any, are the side effects of generating electricity this way, other than lowering the speed of the water going through the membrane? Also, the article didn't mention the power density of the membrane, which matters for making this work without covering river mouths.
- mchannon 8y agoThere are a couple more things you need for this to make electricity: •Wire. Whatever goop makes up this membrane is not going to be able to send all that energy back to the desired destination. I'd expect you to have to come with some kind of metallization and tabbing not unlike what you find on solar cells. •Electrical insulation. At least with solar cells the plus and minus sides are pretty well insulated from each other. Wet goop on the other hand, not so much, and with water occasionally flowing around the edges to shunt the power produced. •MPPT. I'd imagine this produces a highly variable low DC voltage, which is guaranteed to not be even close to the highly stable high AC voltage you want to provide, so you need these boppers. Luckily, PV has made them cheap. Unluckily, they're not waterproof. •Lots of pressurized freshwater, and lots of pressurized saline water. Eventually, it'll all be saline, unless you have streams or rivers or other naturally charged sources. When it's all saline, power output goes to zero. When it's the dry season and the river dries up, power output goes to zero. When sea levels go up a foot, well, you know. In the end, the amount of available surface area, if we spent trillions on R&D to make the perfect design of these, and resigned ourselves to killing all the species at this halocline and making river mouths nonnavigable, would probably be rated less than a couple conventional hydro plants. Efficiency is a red herring, and many devices (thermoelectric generators in particular) become more useful the less efficient they get.
- warent 8y ago"Efficiency is a red herring, and many devices (thermoelectric generators in particular) become more useful the less efficient they get." I don't understand this part. How does a thermoelectric generator become more useful with less efficiency?
- badosu 8y agoAs I understand they mean that a thermoelectric generator is much more useful in small scales of size and weight, where it can't operate very efficiently. It's primary application being for spacecraft since it can have a decent power output for a very long time, which is what's typically required from a long standing mission.
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- markhahn 8y agoany differential can generate power - what am I missing here?
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- punnerud 8y agoOur try in Norway on a large osmosis plant: https://en.m.wikipedia.org/wiki/Statkraft_osmotic_power_prototype_in_Hurum https://en.m.wikipedia.org/wiki/Statkraft_osmotic_power_prot... Crossing fingers that this could reignite the view on osmosis.
- solarkraft 8y agoI am no expert, but I think I have seen such a thing about 10 years ago and this article doesn't explain how it would be any different. Also, here's why this thing, even with the technology completely perfected (100% efficiency), would be absolutely terrible: You're turning valuable fresh water into mostly unusable salt water.
- hannob 8y agoThe idea isn't new. It's been tried before in Norway, unfortunately not very successful: https://en.wikipedia.org/wiki/Statkraft_osmotic_power_prototype_in_Hurum https://en.wikipedia.org/wiki/Statkraft_osmotic_power_protot...