6 ms·

Desalination seems to be well-positioned to take advantage of variable energy prices, particularly in dry-summer climates where demand for water increases at th

by scythe 3y ago

Desalination seems to be well-positioned to take advantage of variable energy prices, particularly in dry-summer climates where demand for water increases at the same time as solar energy availability. If you run the desalination system when energy is cheapest, your energy storage problem becomes a water storage problem, but a simpler one than with pumped-hydroelectric storage. I haven't seen a detailed analysis, but this could look good for California, notwithstanding the other problems with desalination (ecological).

10u152 3y ago
Absolutely, but it's a scale problem. Say you want to produce 1000m3 a day. Well you can build a small plant that makes 41m3 ish an hour and run it 24/7. If you want to produce 1000m3 a day in the three or four hours where solar energy is very cheap you need a plant that does 250m3 an hour - or about 5x the size. So your energy is cheaper but your capital cost is 5x or so.
- scythe 3y ago
  If you save enough on energy, you can switch your system to save on capital. RO has a fancy nanostructured membrane but electrodialysis or MSF might be easier to build at the cost of 20-50% worse efficiency.
- gonzo41 3y ago
  If you build a few batteries next to the plant and that problem is solved.
  - 10u152 3y ago
    That also increases capital costs, putting us back to square 1. Also, have a look at the energy requirements of desal plants. "a few batteries" is pretty gargantuan hand waving
  - dimitar 3y ago
    Or you can build reservoirs for freshwater
    - jvanderbot 3y ago
      Very much. Or pump it into aquifers.
      - ehnto 3y ago
        Maybe the storage could be part of the energy solution, by pumping to an uphill resovior when power is cheap, and sending it through to downhill resoviors via a hydroplant during the peak hours.
        Maxion 3y ago
        I don't think there are very many places that pumped hydro can be built, where it hasn't been built. You also need quite the significant height difference for it to be meaningfull.
      - 10u152 3y ago
        That helps with storage on the output side. But what about the issues/capital costs/resource/labour usage of building huge capacity plant that only gets used 15% of the day?
        jvanderbot 3y ago
        I don't understand the question. Why can we only pump into aquifers 15% of the day? The point of having massive storage is that you can build a smaller plan and run it all day. But anyway, arguments about cost of making drinking water are moot. We need it, so eventually all options will be explored as needs increase.
- BobbyJo 3y ago
  It is very likely that costs would scale sub-linearly. So that 5x is likely dramatically overestimating the increase in capital requirements.
  - lazide 3y ago
    Maintenance on less-consistently run plants is much higher.
  - 10u152 3y ago
    Even so - from a usage of the worlds resources point of view, have 5x oversized equipment idling for 75% of the day is not ideal.
- femto 3y ago
  Maybe it could be combined with pumped hydro? Pump the water to a higher elevation during daylight hours, then use the pressure of the elevated water to drive osmosis based desalination around the clock. You would have to build a reserviour, but it only has to be big enough to hold 24 hours worth of water. If there is not a high enough hill, some/all of the elevation difference can be in the form of a hole, such as an old mine.
  - UnlockedSecrets 3y ago
    The requirement for a large high-low point for pumped storage to be effective would limit it to a few areas wherein it could be viable. I imagine other energy storage technologies would be more viable.
  - 10u152 3y ago
    There's inherently no advantage to just taping the two things together. The idea is to make drinking water. Storing energy is a separate challenge. There's no advantage to combining the two.
  - elmolino89 3y ago
    Assuming you use the sea water: in a hot climate if the reservoir is exposed evaporation will make the water more salty. Building covered elevated cisterns just for the salty water energy storage may be too costly compared to other options, not to mention the risk of creating a salty desert / contaminated aquifer in the case if it leaks out. Also desalinated water does not to be used the moment it is produced. One can run desalination facility at full blast during the day using renewable energy and at a lower or even trickling speed during the night using cheaper, often wasted otherwise energy from the grid.
    - femto 3y ago
      > One can run desalination facility at full blast during the day The advantage is that you need a smaller desalination facility, as it can run at 100% duty cycle. Pumped hydroelectricity could do something similar, but why not have a go at removing the losses of converting back to electricity. (Then again, if you have an electric pump you already have most of the equipment required to produce hydroelectricity by running it in reverse, so pumped hydro might be better because it is more versatile?)
BurningFrog 3y ago
The only ecological problem I've heard of is pumping back the extra saline water to the ocean. Which to me sounds completely negligible in real world terms.
- schiffern 3y ago
  The problem isn't "the ocean." The problem is the brine sinks and forms a hypersaline layer, creating a dead zone in coastal waters which are typically highly biodiverse. https://www.unep.org/news-and-stories/story/five-things-know-about-desalination https://www.unep.org/news-and-stories/story/five-things-know... https://web.archive.org/web/20190114220150/https://www.reuters.com/article/us-environment-brine-idUSKCN1P81PX https://web.archive.org/web/20190114220150/https://www.reute...
  - kgermino 3y ago
    How far away from the shore would you need to go? I imagine it would be fairly easy to pipe the brine a few miles off shore to deeper waters. I have no idea how much of an impact that would have though.
  - BurningFrog 3y ago
    Without any estimates of magnitudes that is meaningless. Of course building infrastructure affects nature, on land and in the oceans.
    - schiffern 3y ago
      > Without any estimates of magnitudes that is meaningless. I see you didn't click my second link, and/or research it yourself. ;) But even if the magnitude of harm were unknown, that doesn't mean we can just default to "ignore it." Additional sources: https://www.frontiersin.org/articles/10.3389/fmars.2022.845113/full https://www.frontiersin.org/articles/10.3389/fmars.2022.8451... https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6959559/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6959559/
      - 3y ago

by scythe 3y ago

10u152 3y ago

Absolutely, but it's a scale problem. Say you want to produce 1000m3 a day. Well you can build a small plant that makes 41m3 ish an hour and run it 24/7. If you want to produce 1000m3 a day in the three or four hours where solar energy is very cheap you need a plant that does 250m3 an hour - or about 5x the size. So your energy is cheaper but your capital cost is 5x or so.

scythe 3y ago
If you save enough on energy, you can switch your system to save on capital. RO has a fancy nanostructured membrane but electrodialysis or MSF might be easier to build at the cost of 20-50% worse efficiency.
gonzo41 3y ago
If you build a few batteries next to the plant and that problem is solved.
- 10u152 3y ago
  That also increases capital costs, putting us back to square 1. Also, have a look at the energy requirements of desal plants. "a few batteries" is pretty gargantuan hand waving
- dimitar 3y ago
  Or you can build reservoirs for freshwater
  - jvanderbot 3y ago
    Very much. Or pump it into aquifers.
    - ehnto 3y ago
      Maybe the storage could be part of the energy solution, by pumping to an uphill resovior when power is cheap, and sending it through to downhill resoviors via a hydroplant during the peak hours.
      - Maxion 3y ago
        I don't think there are very many places that pumped hydro can be built, where it hasn't been built. You also need quite the significant height difference for it to be meaningfull.
    - 10u152 3y ago
      That helps with storage on the output side. But what about the issues/capital costs/resource/labour usage of building huge capacity plant that only gets used 15% of the day?
      - jvanderbot 3y ago
        I don't understand the question. Why can we only pump into aquifers 15% of the day? The point of having massive storage is that you can build a smaller plan and run it all day. But anyway, arguments about cost of making drinking water are moot. We need it, so eventually all options will be explored as needs increase.
BobbyJo 3y ago
It is very likely that costs would scale sub-linearly. So that 5x is likely dramatically overestimating the increase in capital requirements.
- lazide 3y ago
  Maintenance on less-consistently run plants is much higher.
- 10u152 3y ago
  Even so - from a usage of the worlds resources point of view, have 5x oversized equipment idling for 75% of the day is not ideal.
femto 3y ago
Maybe it could be combined with pumped hydro? Pump the water to a higher elevation during daylight hours, then use the pressure of the elevated water to drive osmosis based desalination around the clock. You would have to build a reserviour, but it only has to be big enough to hold 24 hours worth of water. If there is not a high enough hill, some/all of the elevation difference can be in the form of a hole, such as an old mine.
- UnlockedSecrets 3y ago
  The requirement for a large high-low point for pumped storage to be effective would limit it to a few areas wherein it could be viable. I imagine other energy storage technologies would be more viable.
- 10u152 3y ago
  There's inherently no advantage to just taping the two things together. The idea is to make drinking water. Storing energy is a separate challenge. There's no advantage to combining the two.
- elmolino89 3y ago
  Assuming you use the sea water: in a hot climate if the reservoir is exposed evaporation will make the water more salty. Building covered elevated cisterns just for the salty water energy storage may be too costly compared to other options, not to mention the risk of creating a salty desert / contaminated aquifer in the case if it leaks out. Also desalinated water does not to be used the moment it is produced. One can run desalination facility at full blast during the day using renewable energy and at a lower or even trickling speed during the night using cheaper, often wasted otherwise energy from the grid.
  - femto 3y ago
    > One can run desalination facility at full blast during the day The advantage is that you need a smaller desalination facility, as it can run at 100% duty cycle. Pumped hydroelectricity could do something similar, but why not have a go at removing the losses of converting back to electricity. (Then again, if you have an electric pump you already have most of the equipment required to produce hydroelectricity by running it in reverse, so pumped hydro might be better because it is more versatile?)

BurningFrog 3y ago

The only ecological problem I've heard of is pumping back the extra saline water to the ocean. Which to me sounds completely negligible in real world terms.

schiffern 3y ago
The problem isn't "the ocean." The problem is the brine sinks and forms a hypersaline layer, creating a dead zone in coastal waters which are typically highly biodiverse. https://www.unep.org/news-and-stories/story/five-things-know-about-desalination https://www.unep.org/news-and-stories/story/five-things-know... https://web.archive.org/web/20190114220150/https://www.reuters.com/article/us-environment-brine-idUSKCN1P81PX https://web.archive.org/web/20190114220150/https://www.reute...
- kgermino 3y ago
  How far away from the shore would you need to go? I imagine it would be fairly easy to pipe the brine a few miles off shore to deeper waters. I have no idea how much of an impact that would have though.
- BurningFrog 3y ago
  Without any estimates of magnitudes that is meaningless. Of course building infrastructure affects nature, on land and in the oceans.
  - schiffern 3y ago
    > Without any estimates of magnitudes that is meaningless. I see you didn't click my second link, and/or research it yourself. ;) But even if the magnitude of harm were unknown, that doesn't mean we can just default to "ignore it." Additional sources: https://www.frontiersin.org/articles/10.3389/fmars.2022.845113/full https://www.frontiersin.org/articles/10.3389/fmars.2022.8451... https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6959559/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6959559/
    - 3y ago