4 ms·

There 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 ener

There 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 ago
  As 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.
- mchannon 8y ago
  When getting down to the nuts and bolts of a Seebeck (thermoelectric) junction, the efficiency is highest when the heat flow is minimized and the temperature difference is minimized. You get no power when those things are minimized, and in fact you want them both as high as possible.
hectormalot 8y ago
Its not even that new, REDstack started a engineering scale trial of salt-potential electricity generation already a few years ago. (https://www.theafsluitdijk.com/projecten/blue-energy/wat-is-het/ https://www.theafsluitdijk.com/projecten/blue-energy/wat-is-...) 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”
- pishpash 8y ago
  This had me thinking, any thermodyanmic (i.e. statistical) potential can be used to generate work, right? There should be all sorts of natural processes that can be hitched to to extract energy.
Dangeranger 8y ago
Instead of using brackish regions like river deltas, wouldn’t it make more sense to setup clusters of floating “lily pad” style DC power plants in tropical areas where the coast experiences regular heavy rainfall? The fresh water would sit atop the surface membrane due to its’ lower density and slowly filter through to the ocean surface. DC could be converted to AC onboard floating stations and transmitted to coastal regions using ocean floor cables.
- mchannon 8y ago
  Let's do the math. Rainiest spot on Earth sea level, say 1 inch freshwater per day, every day, and somehow consistent all year. 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.
  - nanomonkey 8y ago
    I would think that you could combine the two. The solar collectors could also funnel rain water to a column of this membrane that is located within the salt water.

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 ago
As 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.
mchannon 8y ago
When getting down to the nuts and bolts of a Seebeck (thermoelectric) junction, the efficiency is highest when the heat flow is minimized and the temperature difference is minimized. You get no power when those things are minimized, and in fact you want them both as high as possible.

hectormalot 8y ago

Its not even that new, REDstack started a engineering scale trial of salt-potential electricity generation already a few years ago. (https://www.theafsluitdijk.com/projecten/blue-energy/wat-is-het/ https://www.theafsluitdijk.com/projecten/blue-energy/wat-is-...) 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”

pishpash 8y ago
This had me thinking, any thermodyanmic (i.e. statistical) potential can be used to generate work, right? There should be all sorts of natural processes that can be hitched to to extract energy.

Dangeranger 8y ago

Instead of using brackish regions like river deltas, wouldn’t it make more sense to setup clusters of floating “lily pad” style DC power plants in tropical areas where the coast experiences regular heavy rainfall? The fresh water would sit atop the surface membrane due to its’ lower density and slowly filter through to the ocean surface. DC could be converted to AC onboard floating stations and transmitted to coastal regions using ocean floor cables.

mchannon 8y ago
Let's do the math. Rainiest spot on Earth sea level, say 1 inch freshwater per day, every day, and somehow consistent all year. 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.
- nanomonkey 8y ago
  I would think that you could combine the two. The solar collectors could also funnel rain water to a column of this membrane that is located within the salt water.