7 ms·

These types of systems are generally not competitive with PV for electricity, since they require a lot of concentrated solar energy thus limiting the options fo

These types of systems are generally not competitive with PV for electricity, since they require a lot of concentrated solar energy thus limiting the options for deployment. However, they are great for generating heat. And with heat you can trivially desalinate water. Since trees can be a nice carbon sink, I've often wondered if this type of scheme might make sense: - Plant heliostat molten salt reactors in desert coastal areas (the concentrated solar kind) - Use generated heat to desalinate water (e.g. Multi-stage flash distillation) - Use desalinated water to provide irrigation - Plant (potentially GMO'ed) trees and other bootstrapping organisms to "green" the desert - Rinse repeat. The net effect is that you can potentially turn large swaths of desert into forests, with minimal external energy requirements (and potentially build an agricultural community around them, more or less self contained in terms of water/energy)

flgb 7y ago
Something like this? https://www.sundropfarms.com/facilities/ https://www.sundropfarms.com/facilities/
- anon1253 7y ago
  Yep! but then with fewer greenhouses so it has more of a https://en.wikipedia.org/wiki/Desert_greening https://en.wikipedia.org/wiki/Desert_greening effect
dreamcompiler 7y ago
Coastal areas (even desert ones) are often plagued by clouds, and clouds are a big problem for concentrated solar. This doesn't make your idea bad but it's an obstacle. Edit: Now that I think more about it, who cares if the heat is less reliable if all you're doing is distilling water? I need to take off my electric generation hat sometimes.
- anon1253 7y ago
  Yeah it does limit it a bit, and if the goal is really to plant trees, then eventually it will be somewhat self defeating as forests cool the air and will generate clouds. On the other hand, desalination doesn't require extremely high temperatures, so it also kinda depends on the heat capacity of the molten salt. It probably also doesn't really have to be 24/7/365. But that's I guess a numbers game, so obviously it has to be modeled first.
gbrown 7y ago
If you're displacing groundwater based desert agriculture, that's one thing, but it's worth keeping in mind that in general, desert != wasteland. Deserts are fragile ecosystems with many rare and specialized plants and animals.
- anon1253 7y ago
  Absolutely, but then again (almost) everything is a fragile ecosystem. And if man-made climate change is real (I'm inclined to believe that), then it's less of an absolute and more of a trade-off ... a tricky one certainly, but already we're seeing deserts expand (https://en.wikipedia.org/wiki/Desertification https://en.wikipedia.org/wiki/Desertification) and there are efforts to prevent it (https://en.wikipedia.org/wiki/Great_Green_Wall https://en.wikipedia.org/wiki/Great_Green_Wall) so it could potentially be another tool.
  - gbrown 7y ago
    For sure, I just don't think we should gloss over the nature of such ecosystems, since many people really don't know.
- chongli 7y ago
  Deserts are fragile ecosystems with many rare and specialized plants and animals. Climate change may push the temperature of some of those deserts too high, wiping out the specialized plants and animals that live there. Perhaps we could use a solar installation to provide shade in areas that are getting too hot.
  - gbrown 7y ago
    I'm well aware, just wanted to point out a fact about an underappreciated ecosystem. I feel the same way when people complain about swamps.
iagovar 7y ago
Hmmm we have multiple CSP plants in southern Spain, I wonder if we could do that, because it has been predicted that Spain will desertify with coming climate changes. My issue is what do we do with the byproducts of desalination? If I did understand it there's no really use for that, and I've seen that other countries just dump it into the water, which is a big no no for local ecosystems (and I guess for oceans ph levels if this becomes widespread).
- anon1253 7y ago
  Straight up dumping it in the ocean is generally considered bad. The standard trick is to wash/mix the brine with fresh ocean water to reduce the concentration of salt before dumping it back. Another interesting byproduct that is often overlooked are the metals and minerals. Things like lithium (and even gold) are relatively abundant in sea water and could be recovered from the brine (at the cost of complexity of course).
  - iagovar 7y ago
    That looks like a large scale operation. CSP is struggling to compete in Spain with PV, but I can see it happening with companies like Acciona or some other spanish utility behemoths.
  - pfdietz 7y ago
    Gold is not abundant in seawater: ~10 parts per trillion by mass.
MichaelApproved 7y ago
The infrastructure to get the salt water to the desert and then to distribute the fresh water to the trees will also be a challenge. There are other challenges that you might not have considered, like sand dunes ruining your progress. China has been working to turn some of it deserts into forests with pretty good success. For the sand dunes issue, they’ve come up with a webbed system that’s fairly easy to deploy. The material is cheap and it’s easy for unskilled labor to deploy. Putting aside the horrible human rights issues with China, it’s amazing to see what they’re doing with infrastructure. Lots of videos on the desert projects, just search for “china desert to forest”. Here’s one of them https://youtu.be/7Nur35fnjDA https://youtu.be/7Nur35fnjDA
- api 7y ago
  In the US Southwest there is the Salton Sea which is an already artificial saline reservoir. Just pipe more ocean into it and use that as the salt water source.
- klyrs 7y ago
  > Putting aside the horrible human rights issues with China, it’s amazing to see what they’re doing with infrastructure. Mussolini got the trains running on time, and China has hundreds of thousands of Uyghur and Muslim people locked away in concentration camps. Do you consider what side of history you're on when you "put aside" such behavior?
  - classicsnoot 7y ago
    1) This is not a constructive comment. Author did not minimize PRC's conduct, or justify it. Rather he negated it from the equation. If PRC's de-desertification strategies were reliant on the prison camps, or in any way contingent, you might have a point. 2) There is no right side of history; there is only what gets remembered and how that memory is portrayed. Consider that America is quite accurately describes as a White Nationalist government for the duration of WWII. One could then frame the war as Nazis and Imperialists being defeated by Communards and White Nationalists with the assistance of Colonizers.
XaspR8d 7y ago
Tangent - is there a systems reason (aside from the "base ecological ethics" of wanting to preserve biodiversity and not eradicate any unique ecosystems) why humans would not want to get rid of deserts? Obviously having more arable or at least livable land is useful to human society, but I generally assume that messing with any large scale climates or biomes has adverse effects. I'm not yet aware of what that would be for deserts though. I suppose they have fairly high albedo, unlike most land formations that can exist in lower latitudes. (To be clear my own views aren't necessarily so utilitarian and I like deserts. Just curious about a rational geoengineering civilization might do.)
- ryanmercer 7y ago
  >Tangent - is there a systems reason (aside from the "base ecological ethics" of wanting to preserve biodiversity and not eradicate any unique ecosystems) why humans would not want to get rid of deserts? Getting rid of deserts could actually be quite bad for other ecosystems. The Amazon is fertilized by the Sahara for example https://www.nasa.gov/content/goddard/nasa-satellite-reveals-how-much-saharan-dust-feeds-amazon-s-plants/ https://www.nasa.gov/content/goddard/nasa-satellite-reveals-...
  - jacobush 7y ago
    That's incredible. I assumed arrogantly it was mostly inert silica, not phosphorous.
    - ryanmercer 7y ago
      Yeah the earth is a very complex system. When YC came out and proposed the idea of proposed turning the Sahara into a bunch of algae ponds [1] I cringed. First the plan requires more power than we currently produce just to pump all the water but then you would drastically reduce how much gets blown over to the Amazon AND you would suddenly introduce a tremendous amount of moisture to the atmosphere which would almost certainly change global weather patterns. All of that moisture could cause a considerable increase in rainfall for somewhere (presumably the Amazon, I don't know anything about weather modelling though and am just guessing) which could be catastrophic for life there and even result in tremendous economic losses. Even relatively small scale geoengineering like damns can have profound negative impacts on ecosystems with some being very predictable and some being completely wildcard. We know the Sahara fertilizes the Amazon but what level does it effect marine life by feeding stuff at the bottom of the food chain (plankton for example) and what would removing that mineral/nutrient source do to the food chain, would it increase rains (and cloud cover) over that area of ocean that might change temperatures subtly enough to make an impact on currents, etc. We're at the point now as a species where we have the power of gods but can't begin to understand the implications of what we are capable of doing. [1] http://carbon.ycombinator.com/desert-flooding/ http://carbon.ycombinator.com/desert-flooding/
mojomark 7y ago
> These types of systems are generally not competitive with PV for electricity, since they require a lot of concentrated solar energy thus limiting the options for deployment. > However, they are great for generating heat. And with heat you can trivially desalinate water. Not trying to be a PITA, but to your first point, suggest you provide a citation if you're going to make a sweeping claim. I'm actually interested in this claim. To your second point, while desalination at scale isn't 'rocket science', it isn't exactly trivial. Having designed and worked on desalination plants for commercial ships, yes, you can buy an off the shelf evaporator. However, you still need to carefully design the heat supply system and pressure regulation. Also, you have to carefully manage the highly corrosive brine discharge. When I say corrosive, I mean this stuff is NASTY. At sea, it's a little easier, because you are constantly moving can kust discharge it overboard (although the environmental impacts are becoming increasingly apparent, so I'm not sure that direct discharge option will last much longer). However, you still need thick/expensive corrosion resistant brine discharge line piping/valves/etc. (or you will be replacing pipe often). Ashore, you need to manage to transport the brine away and somehow dilute it to a point where it's non-toxic. You also have to carefully manage scaling inside of the evaporator, and I'm telling you this scaling is not something you can just brush off. This stuff is like a mollusk she'll coating on all of your internally heat transfer surfaces. If you can remove it with a chisel and hammer and not damage your system, you're a better person than I. I'm not saying it's not doable, there are land-based desalination plants all over the place. I'm just saying it's not as simple as running some heating coils in a tub of water and collecting the evaporated water.
- jfoutz 7y ago
  This is a fascinating comment. In a municipal environment, would standard remediation of sewer water be good enough to dilute the brine? It seems like you could get something close to a closed loop. Obviously some water would be lost to evaporation, but in a city a lot of water comes out of the tap, over dishes or people or laundry, and then right back down the drain. It's not drinkable anymore, but we've got lots of tools to make it reasonably cleanish enough to put in a river. Would using that gray water to dilute brine alleviate some of that pain? I'm not remotely an expert in this area, just spitballing here. But you clearly have some experience. I'm curious if closing the loop might be enough to make such a system workable.
adrianN 7y ago
You should check first that lowering the desert's albedo with trees is not worse than keeping the CO2 in the air.
reaperducer 7y ago
These types of systems are generally not competitive with PV for electricity You should tell that to the people who built at least a dozen of these plants in the American west, with more to come. Right now there are at least four that I've seen in Nevada exporting electricity to California.
- anon1253 7y ago
  There is a good map on the wiki of Concentrated Solar [1] showing the Direct Normal Irradiation. The US West coast is in somewhat of a unique position (as is Australia, South Africa, and a couple of others I suppose): high density population centers in areas with a lot of solar radiation. In those areas it might very well be the best method available (dunno, could be). Transporting electricity at distance is non-trivial however. Plans to put these installations in the Sahara and transport it to Europe via high-voltage DC lines have pretty much gone nowhere (https://en.wikipedia.org/wiki/Desertec https://en.wikipedia.org/wiki/Desertec). So non-competitive was more a reference to the constraints that it imposes, but I could've been clearer for sure. [1]: https://upload.wikimedia.org/wikipedia/commons/c/c7/Global_Map_of_Direct_Normal_Radiation_01.png https://upload.wikimedia.org/wikipedia/commons/c/c7/Global_M...
tomas789 7y ago
This would only lead to a constant shift in total CO2 emissions because there is only so much space you can utilize. When a plant dies it releases the CO2 back to the atmosphere. For the money, you can likely get higher CO2 abatement (i.e. close a coal fired power plant and replace it with renewables subsidy). In the first case, you save the CO2 roughly equivalent to the total weight of the plants. In the pther case, you save x tonnes of CO2 every year.
- anon1253 7y ago
  True, but planting trees as a method for carbon sequestering is not a novel idea, and currently seems one of the better short-term options. Long term it's not that great for the reason you mentioned, and there is quite a lot of debate about it going on right now. https://science.sciencemag.org/content/365/6448/76 https://science.sciencemag.org/content/365/6448/76 https://www.nature.com/articles/d41586-019-00122-z https://www.nature.com/articles/d41586-019-00122-z for two more or less competing views.
numtel 7y ago
Pretty soon we won't even need all these parts. If Metal-Organic Frameworks (MOF) take off like these reports describe, we'll be able to irrigate deserts passively. https://www.youtube.com/watch?v=XPSYzLZ7xKU https://www.youtube.com/watch?v=XPSYzLZ7xKU https://www.sciencemag.org/news/2019/09/crystalline-nets-harvest-water-desert-air-turn-carbon-dioxide-liquid-fuel https://www.sciencemag.org/news/2019/09/crystalline-nets-har...

flgb 7y ago

Something like this? https://www.sundropfarms.com/facilities/ https://www.sundropfarms.com/facilities/

anon1253 7y ago
Yep! but then with fewer greenhouses so it has more of a https://en.wikipedia.org/wiki/Desert_greening https://en.wikipedia.org/wiki/Desert_greening effect

dreamcompiler 7y ago

Coastal areas (even desert ones) are often plagued by clouds, and clouds are a big problem for concentrated solar. This doesn't make your idea bad but it's an obstacle. Edit: Now that I think more about it, who cares if the heat is less reliable if all you're doing is distilling water? I need to take off my electric generation hat sometimes.

anon1253 7y ago
Yeah it does limit it a bit, and if the goal is really to plant trees, then eventually it will be somewhat self defeating as forests cool the air and will generate clouds. On the other hand, desalination doesn't require extremely high temperatures, so it also kinda depends on the heat capacity of the molten salt. It probably also doesn't really have to be 24/7/365. But that's I guess a numbers game, so obviously it has to be modeled first.

gbrown 7y ago

If you're displacing groundwater based desert agriculture, that's one thing, but it's worth keeping in mind that in general, desert != wasteland. Deserts are fragile ecosystems with many rare and specialized plants and animals.

anon1253 7y ago
Absolutely, but then again (almost) everything is a fragile ecosystem. And if man-made climate change is real (I'm inclined to believe that), then it's less of an absolute and more of a trade-off ... a tricky one certainly, but already we're seeing deserts expand (https://en.wikipedia.org/wiki/Desertification https://en.wikipedia.org/wiki/Desertification) and there are efforts to prevent it (https://en.wikipedia.org/wiki/Great_Green_Wall https://en.wikipedia.org/wiki/Great_Green_Wall) so it could potentially be another tool.
- gbrown 7y ago
  For sure, I just don't think we should gloss over the nature of such ecosystems, since many people really don't know.
chongli 7y ago
Deserts are fragile ecosystems with many rare and specialized plants and animals. Climate change may push the temperature of some of those deserts too high, wiping out the specialized plants and animals that live there. Perhaps we could use a solar installation to provide shade in areas that are getting too hot.
- gbrown 7y ago
  I'm well aware, just wanted to point out a fact about an underappreciated ecosystem. I feel the same way when people complain about swamps.

iagovar 7y ago

Hmmm we have multiple CSP plants in southern Spain, I wonder if we could do that, because it has been predicted that Spain will desertify with coming climate changes. My issue is what do we do with the byproducts of desalination? If I did understand it there's no really use for that, and I've seen that other countries just dump it into the water, which is a big no no for local ecosystems (and I guess for oceans ph levels if this becomes widespread).

anon1253 7y ago
Straight up dumping it in the ocean is generally considered bad. The standard trick is to wash/mix the brine with fresh ocean water to reduce the concentration of salt before dumping it back. Another interesting byproduct that is often overlooked are the metals and minerals. Things like lithium (and even gold) are relatively abundant in sea water and could be recovered from the brine (at the cost of complexity of course).
- iagovar 7y ago
  That looks like a large scale operation. CSP is struggling to compete in Spain with PV, but I can see it happening with companies like Acciona or some other spanish utility behemoths.
- pfdietz 7y ago
  Gold is not abundant in seawater: ~10 parts per trillion by mass.

MichaelApproved 7y ago

The infrastructure to get the salt water to the desert and then to distribute the fresh water to the trees will also be a challenge. There are other challenges that you might not have considered, like sand dunes ruining your progress. China has been working to turn some of it deserts into forests with pretty good success. For the sand dunes issue, they’ve come up with a webbed system that’s fairly easy to deploy. The material is cheap and it’s easy for unskilled labor to deploy. Putting aside the horrible human rights issues with China, it’s amazing to see what they’re doing with infrastructure. Lots of videos on the desert projects, just search for “china desert to forest”. Here’s one of them https://youtu.be/7Nur35fnjDA https://youtu.be/7Nur35fnjDA

api 7y ago
In the US Southwest there is the Salton Sea which is an already artificial saline reservoir. Just pipe more ocean into it and use that as the salt water source.
klyrs 7y ago
> Putting aside the horrible human rights issues with China, it’s amazing to see what they’re doing with infrastructure. Mussolini got the trains running on time, and China has hundreds of thousands of Uyghur and Muslim people locked away in concentration camps. Do you consider what side of history you're on when you "put aside" such behavior?
- classicsnoot 7y ago
  1) This is not a constructive comment. Author did not minimize PRC's conduct, or justify it. Rather he negated it from the equation. If PRC's de-desertification strategies were reliant on the prison camps, or in any way contingent, you might have a point. 2) There is no right side of history; there is only what gets remembered and how that memory is portrayed. Consider that America is quite accurately describes as a White Nationalist government for the duration of WWII. One could then frame the war as Nazis and Imperialists being defeated by Communards and White Nationalists with the assistance of Colonizers.

XaspR8d 7y ago

Tangent - is there a systems reason (aside from the "base ecological ethics" of wanting to preserve biodiversity and not eradicate any unique ecosystems) why humans would not want to get rid of deserts? Obviously having more arable or at least livable land is useful to human society, but I generally assume that messing with any large scale climates or biomes has adverse effects. I'm not yet aware of what that would be for deserts though. I suppose they have fairly high albedo, unlike most land formations that can exist in lower latitudes. (To be clear my own views aren't necessarily so utilitarian and I like deserts. Just curious about a rational geoengineering civilization might do.)

ryanmercer 7y ago
>Tangent - is there a systems reason (aside from the "base ecological ethics" of wanting to preserve biodiversity and not eradicate any unique ecosystems) why humans would not want to get rid of deserts? Getting rid of deserts could actually be quite bad for other ecosystems. The Amazon is fertilized by the Sahara for example https://www.nasa.gov/content/goddard/nasa-satellite-reveals-how-much-saharan-dust-feeds-amazon-s-plants/ https://www.nasa.gov/content/goddard/nasa-satellite-reveals-...
- jacobush 7y ago
  That's incredible. I assumed arrogantly it was mostly inert silica, not phosphorous.
  - ryanmercer 7y ago
    Yeah the earth is a very complex system. When YC came out and proposed the idea of proposed turning the Sahara into a bunch of algae ponds [1] I cringed. First the plan requires more power than we currently produce just to pump all the water but then you would drastically reduce how much gets blown over to the Amazon AND you would suddenly introduce a tremendous amount of moisture to the atmosphere which would almost certainly change global weather patterns. All of that moisture could cause a considerable increase in rainfall for somewhere (presumably the Amazon, I don't know anything about weather modelling though and am just guessing) which could be catastrophic for life there and even result in tremendous economic losses. Even relatively small scale geoengineering like damns can have profound negative impacts on ecosystems with some being very predictable and some being completely wildcard. We know the Sahara fertilizes the Amazon but what level does it effect marine life by feeding stuff at the bottom of the food chain (plankton for example) and what would removing that mineral/nutrient source do to the food chain, would it increase rains (and cloud cover) over that area of ocean that might change temperatures subtly enough to make an impact on currents, etc. We're at the point now as a species where we have the power of gods but can't begin to understand the implications of what we are capable of doing. [1] http://carbon.ycombinator.com/desert-flooding/ http://carbon.ycombinator.com/desert-flooding/

mojomark 7y ago

> These types of systems are generally not competitive with PV for electricity, since they require a lot of concentrated solar energy thus limiting the options for deployment. > However, they are great for generating heat. And with heat you can trivially desalinate water. Not trying to be a PITA, but to your first point, suggest you provide a citation if you're going to make a sweeping claim. I'm actually interested in this claim. To your second point, while desalination at scale isn't 'rocket science', it isn't exactly trivial. Having designed and worked on desalination plants for commercial ships, yes, you can buy an off the shelf evaporator. However, you still need to carefully design the heat supply system and pressure regulation. Also, you have to carefully manage the highly corrosive brine discharge. When I say corrosive, I mean this stuff is NASTY. At sea, it's a little easier, because you are constantly moving can kust discharge it overboard (although the environmental impacts are becoming increasingly apparent, so I'm not sure that direct discharge option will last much longer). However, you still need thick/expensive corrosion resistant brine discharge line piping/valves/etc. (or you will be replacing pipe often). Ashore, you need to manage to transport the brine away and somehow dilute it to a point where it's non-toxic. You also have to carefully manage scaling inside of the evaporator, and I'm telling you this scaling is not something you can just brush off. This stuff is like a mollusk she'll coating on all of your internally heat transfer surfaces. If you can remove it with a chisel and hammer and not damage your system, you're a better person than I. I'm not saying it's not doable, there are land-based desalination plants all over the place. I'm just saying it's not as simple as running some heating coils in a tub of water and collecting the evaporated water.

jfoutz 7y ago
This is a fascinating comment. In a municipal environment, would standard remediation of sewer water be good enough to dilute the brine? It seems like you could get something close to a closed loop. Obviously some water would be lost to evaporation, but in a city a lot of water comes out of the tap, over dishes or people or laundry, and then right back down the drain. It's not drinkable anymore, but we've got lots of tools to make it reasonably cleanish enough to put in a river. Would using that gray water to dilute brine alleviate some of that pain? I'm not remotely an expert in this area, just spitballing here. But you clearly have some experience. I'm curious if closing the loop might be enough to make such a system workable.

adrianN 7y ago

You should check first that lowering the desert's albedo with trees is not worse than keeping the CO2 in the air.

reaperducer 7y ago

These types of systems are generally not competitive with PV for electricity You should tell that to the people who built at least a dozen of these plants in the American west, with more to come. Right now there are at least four that I've seen in Nevada exporting electricity to California.

anon1253 7y ago
There is a good map on the wiki of Concentrated Solar [1] showing the Direct Normal Irradiation. The US West coast is in somewhat of a unique position (as is Australia, South Africa, and a couple of others I suppose): high density population centers in areas with a lot of solar radiation. In those areas it might very well be the best method available (dunno, could be). Transporting electricity at distance is non-trivial however. Plans to put these installations in the Sahara and transport it to Europe via high-voltage DC lines have pretty much gone nowhere (https://en.wikipedia.org/wiki/Desertec https://en.wikipedia.org/wiki/Desertec). So non-competitive was more a reference to the constraints that it imposes, but I could've been clearer for sure. [1]: https://upload.wikimedia.org/wikipedia/commons/c/c7/Global_Map_of_Direct_Normal_Radiation_01.png https://upload.wikimedia.org/wikipedia/commons/c/c7/Global_M...

tomas789 7y ago

This would only lead to a constant shift in total CO2 emissions because there is only so much space you can utilize. When a plant dies it releases the CO2 back to the atmosphere. For the money, you can likely get higher CO2 abatement (i.e. close a coal fired power plant and replace it with renewables subsidy). In the first case, you save the CO2 roughly equivalent to the total weight of the plants. In the pther case, you save x tonnes of CO2 every year.

anon1253 7y ago
True, but planting trees as a method for carbon sequestering is not a novel idea, and currently seems one of the better short-term options. Long term it's not that great for the reason you mentioned, and there is quite a lot of debate about it going on right now. https://science.sciencemag.org/content/365/6448/76 https://science.sciencemag.org/content/365/6448/76 https://www.nature.com/articles/d41586-019-00122-z https://www.nature.com/articles/d41586-019-00122-z for two more or less competing views.

numtel 7y ago

Pretty soon we won't even need all these parts. If Metal-Organic Frameworks (MOF) take off like these reports describe, we'll be able to irrigate deserts passively. https://www.youtube.com/watch?v=XPSYzLZ7xKU https://www.youtube.com/watch?v=XPSYzLZ7xKU https://www.sciencemag.org/news/2019/09/crystalline-nets-harvest-water-desert-air-turn-carbon-dioxide-liquid-fuel https://www.sciencemag.org/news/2019/09/crystalline-nets-har...