4 ms·

Might come down to things like, how efficient are cranes & conveyors & so forth, vs water pumps & hydro generators. The nature of each material leads to differe

by st26 8y ago

Might come down to things like, how efficient are cranes & conveyors & so forth, vs water pumps & hydro generators. The nature of each material leads to different techniques which could have very different efficiencies.

hinkley 8y ago
Upfront costs can sink a project, but so can ongoing maintenance. Materials that don't foul as easily have a long term advantage. And when there's a drought people won't be too happy about all that fresh water you're taking to make electricity ('course, how much water does it take to make a cubic foot of concrete, cradle to grave?).
- mmt 8y ago
  > how much water does it take to make a cubic foot of concrete The article does mention that they expect to use 1/6th the cement of construction concrete. This paper https://www.nature.com/articles/s41893-017-0009-5 https://www.nature.com/articles/s41893-017-0009-5 gives an idea: 2 Gt of water per 21.3 Gt of not-water. Assuming perfectly dry concrete (and none of the water converting to not-water mass, both of which I believe are counter-factual), that means a 2130 kg block of concrete would have needed 200 kg of water. Pumped hydro, assuming identical efficiency, would need all 2130 kg of water.
  - hinkley 8y ago
    2Gt of water was mixed into the concrete, but when you're calculating water footprint you need to look at how much water went into creating all of the ingredients. That can be pretty substantial. That article does go on to cover the water footprint, but what troubles me is that they switch units, and report it as 16.6km^3 of water. Which seems like they're trying to obfuscate the results (they have obfuscated them, whether that was intentional or not is another question). That's all the water for all the concrete. Which for a hydroelectric perspective, is about 5% of the volume of water behind Grand Coulee Dam, for all the concrete we currently make every year. So maybe concrete blocks make sense for power.
    - CydeWeys 8y ago
      Here's an idea: It's possible to make unreinforced concrete using seawater. Wonder if that would work here.
    - deleted 8y ago
      [deleted]
    - mmt 8y ago
      > 2Gt of water was mixed into the concrete, but when you're calculating water footprint you need to look at how much water went into creating all of the ingredients. True, though the paper makes a point, early on, that much of it is used in producing the aggregate, and the article makes a point of (potentially) using recycled/discarded aggregate, which would incur no additional water consumption. > report it as 16.6km^3 of water. Which seems like they're trying to obfuscate the results That's a remarkably harsh characterization, especially since that was parenthetical. The main reported amount was 16.6 × 10^9 m^3. With water having the convenient density of 1000kg/m^3 (1 ton/m^3) and 10^9 being equivalent to the SI G prefix (both facts which one reasonably expect a reader of a physical sciences journal to know casually), it seems hardly obfuscatory. I'd attribute, instead, a change of units to a desire to compare it to household use, later in that paragraph, which is more typically measured by volume. Although for commercial concrete block of 2130kg, that would, indeed, change the amount of water to be 1660kg from my original 200kg. However, I'm fairly confident that the ability to use 1/6th the cement combined with not needing any particular aggregate (even recycled) will bring the number for the article's application much closer to the smaller one than the larger one.
mikec3010 8y ago
I wonder if you could compromise and use powdered concrete in a closed system? High powered fans could blow the fine powder upward in a silo so it would act like a liquid. Then large paddlewheels catching the powder could power a generator coming back down. I have no idea if powder going up a tube has less friction than blocks on a cable/pulley, however.
- effie 8y ago
  That's not a good idea. You would have turbulent airflow with dust, most energy would get lost, resulting in low efficiency. Weights on cables pulled by electric motors is as efficient as it gets. Not to mention dust bucking up the gears and sockets.
PeterisP 8y ago
The efficiency is comparable, pumped hydro gets ~80% at large scale practice, while this is promised to be 85% and might turn out to be the same after all the implementation issues and wear&tear comes in. Which it should be - IMHO, despite the material, both systems get very similar techniques, at the core in both cases you have the loss of a motor+generator pair plus the friction of your mechanical system.

by st26 8y ago

hinkley 8y ago

Upfront costs can sink a project, but so can ongoing maintenance. Materials that don't foul as easily have a long term advantage. And when there's a drought people won't be too happy about all that fresh water you're taking to make electricity ('course, how much water does it take to make a cubic foot of concrete, cradle to grave?).

mmt 8y ago
> how much water does it take to make a cubic foot of concrete The article does mention that they expect to use 1/6th the cement of construction concrete. This paper https://www.nature.com/articles/s41893-017-0009-5 https://www.nature.com/articles/s41893-017-0009-5 gives an idea: 2 Gt of water per 21.3 Gt of not-water. Assuming perfectly dry concrete (and none of the water converting to not-water mass, both of which I believe are counter-factual), that means a 2130 kg block of concrete would have needed 200 kg of water. Pumped hydro, assuming identical efficiency, would need all 2130 kg of water.
- hinkley 8y ago
  2Gt of water was mixed into the concrete, but when you're calculating water footprint you need to look at how much water went into creating all of the ingredients. That can be pretty substantial. That article does go on to cover the water footprint, but what troubles me is that they switch units, and report it as 16.6km^3 of water. Which seems like they're trying to obfuscate the results (they have obfuscated them, whether that was intentional or not is another question). That's all the water for all the concrete. Which for a hydroelectric perspective, is about 5% of the volume of water behind Grand Coulee Dam, for all the concrete we currently make every year. So maybe concrete blocks make sense for power.
  - CydeWeys 8y ago
    Here's an idea: It's possible to make unreinforced concrete using seawater. Wonder if that would work here.
  - deleted 8y ago
    [deleted]
  - mmt 8y ago
    > 2Gt of water was mixed into the concrete, but when you're calculating water footprint you need to look at how much water went into creating all of the ingredients. True, though the paper makes a point, early on, that much of it is used in producing the aggregate, and the article makes a point of (potentially) using recycled/discarded aggregate, which would incur no additional water consumption. > report it as 16.6km^3 of water. Which seems like they're trying to obfuscate the results That's a remarkably harsh characterization, especially since that was parenthetical. The main reported amount was 16.6 × 10^9 m^3. With water having the convenient density of 1000kg/m^3 (1 ton/m^3) and 10^9 being equivalent to the SI G prefix (both facts which one reasonably expect a reader of a physical sciences journal to know casually), it seems hardly obfuscatory. I'd attribute, instead, a change of units to a desire to compare it to household use, later in that paragraph, which is more typically measured by volume. Although for commercial concrete block of 2130kg, that would, indeed, change the amount of water to be 1660kg from my original 200kg. However, I'm fairly confident that the ability to use 1/6th the cement combined with not needing any particular aggregate (even recycled) will bring the number for the article's application much closer to the smaller one than the larger one.

mikec3010 8y ago

I wonder if you could compromise and use powdered concrete in a closed system? High powered fans could blow the fine powder upward in a silo so it would act like a liquid. Then large paddlewheels catching the powder could power a generator coming back down. I have no idea if powder going up a tube has less friction than blocks on a cable/pulley, however.

effie 8y ago
That's not a good idea. You would have turbulent airflow with dust, most energy would get lost, resulting in low efficiency. Weights on cables pulled by electric motors is as efficient as it gets. Not to mention dust bucking up the gears and sockets.

PeterisP 8y ago

The efficiency is comparable, pumped hydro gets ~80% at large scale practice, while this is promised to be 85% and might turn out to be the same after all the implementation issues and wear&tear comes in. Which it should be - IMHO, despite the material, both systems get very similar techniques, at the core in both cases you have the loss of a motor+generator pair plus the friction of your mechanical system.