4 ms·

With your desal example, I think a bulk of the energy requirement for desalination is building a pressure differential. That seems like it would be very easy to

With your desal example, I think a bulk of the energy requirement for desalination is building a pressure differential. That seems like it would be very easy to parallelize.. you don't need full on duplicative Desalination sites, you just need pressure vessels that can store large amounts of compressed air to take advantage of energy gluts.

DoctorOetker 8y ago
I thought they used electricity to deionize salt water, the salts are already dissociated into positive and negative ions, so pass a current through the water, and every now and then raise the electrodes out, mechanically scrape it off or reverse current in dump brine to remove the ions...
- amluto 8y ago
  Doesn’t work. By the time you’ve moved any non-negligible amount of ions, you’ve built up an insane amount of charge and hence voltage. That voltage will be impossible to work with, not to mention many orders of magnitude higher than the voltage needed to split water into H2 and O2. One mole of singly charged ions is ~1e5 Coulombs. At an insanely high capacitance of 1 Farad (which you’ll never see in such an application) that’s 100kV of static charge by the time you move a few grams of salt. This is why you essentially never encounter ions by themselves.
  - mikec3010 8y ago
    Could you store electrical energy this way more efficiently than pumped hydroelectric? Like make a capacitor the size of a wastewater storage tank?
    - logfromblammo 8y ago
      Wouldn't it self-discharge? And at that size, also blow itself up?
    - amluto 8y ago
      There are devices called “supercapacitors” that work a little bit like this. They have rather weird electrical characteristics. I think they’re occasionally used as car starter batteries, but they’re mostly used as very long-lasting devices that can store a moderate amount of energy for backup use. I have a nifty DIMM with some supercapacitors that power a circuit that will wrote the contents back to flash if the power fails.
  - DoctorOetker 8y ago
    I was thinking of https://en.wikipedia.org/wiki/Capacitive_deionization https://en.wikipedia.org/wiki/Capacitive_deionization I was wrong about the desorption step, I thought they scraped the ions off... Incidentally at that page: "Part of the energy input required during the adsorption phase can be recovered during this desorption step. " With enough of those electrodes, can't we use the sea as a big electrolyte battery? the energy is storedd capacitively
- bluGill 8y ago
  There are two major ways to do it at scale: Distillation, or reverse osmosis. In large plants they are actually energy competitive - reverse osmosis needs pumps to build pressure. Distillation needs energy to boil water, but then that steam is cooled down with the input water which gets heated in turn. I'm not aware of any large scale ion plants, I don't know if the chemistry can work or not.
  - ethagknight 8y ago
    Or boil via vacuum
kpil 8y ago
If you can store large amounts of compressed air to take advantage of energy gluts, it's probably better to just storing it and generate electricity to sell on the market when the price is high...

DoctorOetker 8y ago

I thought they used electricity to deionize salt water, the salts are already dissociated into positive and negative ions, so pass a current through the water, and every now and then raise the electrodes out, mechanically scrape it off or reverse current in dump brine to remove the ions...

amluto 8y ago
Doesn’t work. By the time you’ve moved any non-negligible amount of ions, you’ve built up an insane amount of charge and hence voltage. That voltage will be impossible to work with, not to mention many orders of magnitude higher than the voltage needed to split water into H2 and O2. One mole of singly charged ions is ~1e5 Coulombs. At an insanely high capacitance of 1 Farad (which you’ll never see in such an application) that’s 100kV of static charge by the time you move a few grams of salt. This is why you essentially never encounter ions by themselves.
- mikec3010 8y ago
  Could you store electrical energy this way more efficiently than pumped hydroelectric? Like make a capacitor the size of a wastewater storage tank?
  - logfromblammo 8y ago
    Wouldn't it self-discharge? And at that size, also blow itself up?
  - amluto 8y ago
    There are devices called “supercapacitors” that work a little bit like this. They have rather weird electrical characteristics. I think they’re occasionally used as car starter batteries, but they’re mostly used as very long-lasting devices that can store a moderate amount of energy for backup use. I have a nifty DIMM with some supercapacitors that power a circuit that will wrote the contents back to flash if the power fails.
- DoctorOetker 8y ago
  I was thinking of https://en.wikipedia.org/wiki/Capacitive_deionization https://en.wikipedia.org/wiki/Capacitive_deionization I was wrong about the desorption step, I thought they scraped the ions off... Incidentally at that page: "Part of the energy input required during the adsorption phase can be recovered during this desorption step. " With enough of those electrodes, can't we use the sea as a big electrolyte battery? the energy is storedd capacitively
bluGill 8y ago
There are two major ways to do it at scale: Distillation, or reverse osmosis. In large plants they are actually energy competitive - reverse osmosis needs pumps to build pressure. Distillation needs energy to boil water, but then that steam is cooled down with the input water which gets heated in turn. I'm not aware of any large scale ion plants, I don't know if the chemistry can work or not.
- ethagknight 8y ago
  Or boil via vacuum

kpil 8y ago

If you can store large amounts of compressed air to take advantage of energy gluts, it's probably better to just storing it and generate electricity to sell on the market when the price is high...