‘Two-faced’ membrane can create electricity from salty and fresh water
sciencemag.org
sciencemag.org
•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.
I don't understand this part. How does a thermoelectric generator become more useful with less efficiency?
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.
You get no power when those things are minimized, and in fact you want them both as high as possible.
Another non-obvious (to me) thing it needs is the ability to drain the brackish water you’re creating. At scale this probably involves at least a long canal or pipe, and makes the setup more difficult that “let’s just put this were the river meets the sea”
One square meter, 100% efficient, looks like it would produce less than 1 kW with a river feeding it. With just rain, figure on well under 100 watts. Probably under 10 watts.
Compare with a floating PV array, also 1 square meter, but real-world 20% efficient cells. In the same rainy rainy spot. Probably much higher than 10 watts, even factoring in nights and overcast skies.
Maybe you could combine them, but I bet you'd get better bang for your buck by just doubling the floating PV array size. PV doesn't need a freshwater (or saline) source either.
If you care about consistent power then you'll need a battery (or grid connection) either way.
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.
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.
Also, as always, curious how having these membranes in the water would affect the local ecosystem.
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=20160...
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.
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.
Crossing fingers that this could reignite the view on osmosis.
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.
https://en.wikipedia.org/wiki/Statkraft_osmotic_power_protot...
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.
Also, the article didn't mention the power density of the membrane, which matters for making this work without covering river mouths.