6 ms·

85% efficiency - wow!

msandford 12y ago
Once you run it through some kind of thermodynamic cycle to turn steam into electricity, the efficiency will drop. There's a limit to how efficient those processes are. For the kinds of temperatures we can easily handle with the technology we have, it's not so rosy. Steam plants are between 30% and 60% efficient depending on how fancy (and thus expensive to build) they are. http://en.wikipedia.org/wiki/Thermal_efficiency http://en.wikipedia.org/wiki/Thermal_efficiency So if you figure the steam plant might be 45% efficient and the steam production is 85% efficient you end up with 0.45 * 0.85 = 38.5% total efficiency. Better than off-the-shelf PV panels available today. But this method requires solar concentration by a factor of 10x which will definitely add cost. If it's better that PV at that point would remain to be seen.
- Someone 12y ago
  On the other hand, 10x concentration is not absurdly high, and if you use this to make tea (that's the kickstarter project) or to purify water (the third world project), you get that 85%.
  - parennoob 12y ago
    This. The applicability of this research to desalination alone makes it hugely useful.
- lotsofmangos 12y ago
  That isn't how it works. The 85% in this case is producing steam that is nowhere near hot enough. A steam plant only gets up to reasonable efficiency when the hot end of the steam plant is at a very high temperature and pressure, which in this case would then react with the carbon element. Have a look at this - "The Mechanism of the Steam-Carbon Reaction" http://rspa.royalsocietypublishing.org/content/193/1034/377 http://rspa.royalsocietypublishing.org/content/193/1034/377
  - msandford 12y ago
    Right, I'm well aware. But I was trying to be conservative as to how pessimistic we should be. We can always be more pessimistic, but we should be no less pessimistic than halving the efficiency. It's not a useful number except to show that on the back of the envelope it's not that great for power generation. The 85% case is probably more about desalinization than it is about making steam to do useful work unless that useful work is heating. A concentrator, some of this stuff and you could make solar powered steam kettles which are very common in large kitchens.
    - lotsofmangos 12y ago
      fair enough, is just that your calculation on power generation put it as being massively better than the best commercially available solar power, which struck me as wildly optimistic
      - msandford 12y ago
        It's only better until you figure in the costs to make it work. Nobody cares about actual efficiency, they care about dollars per watt. Even at 38% (which you can't get) there's no way it would be cheaper than PV because of all the infrastructure you'd need to concentrate sunlight and do all the piping, etc.
- chr1 12y ago
  Though you don't necessarily need to convert it to electricity, and can use the steam for something else, like desalination of sea water.
  - waps 12y ago
    Nothing lasts in sea water. Least of all sponges. I doubt that's a practical application.
    - kordless 12y ago
      Just wash it off.
      - waps 12y ago
        Incidently, detergent is one of those things that won't work well in seawater. Plus seawater is corrosive. So even if you do manage to clean things, they're not as reusable as they otherwise would be.
lotsofmangos 12y ago
85% efficient at taking heat and using it to evaporate water isn't that high, they are not talking about thermodynamic cycles producing work. This doesn't look like something you would use to drive an engine with as for that you want the high temperatures that go with the high concentration of sunlight, as the amount of work you can get out is directly related to the relative distance of the hot and the cold end from 0K. edit: 0 - you must play the game 1 - you can never win 2 - you can only break even on a very cold day 3 - it never gets that cold

Once you run it through some kind of thermodynamic cycle to turn steam into electricity, the efficiency will drop. There's a limit to how efficient those processes are. For the kinds of temperatures we can easily handle with the technology we have, it's not so rosy. Steam plants are between 30% and 60% efficient depending on how fancy (and thus expensive to build) they are. http://en.wikipedia.org/wiki/Thermal_efficiency http://en.wikipedia.org/wiki/Thermal_efficiency So if you figure the steam plant might be 45% efficient and the steam production is 85% efficient you end up with 0.45 * 0.85 = 38.5% total efficiency. Better than off-the-shelf PV panels available today. But this method requires solar concentration by a factor of 10x which will definitely add cost. If it's better that PV at that point would remain to be seen.

Someone 12y ago
On the other hand, 10x concentration is not absurdly high, and if you use this to make tea (that's the kickstarter project) or to purify water (the third world project), you get that 85%.
- parennoob 12y ago
  This. The applicability of this research to desalination alone makes it hugely useful.
lotsofmangos 12y ago
That isn't how it works. The 85% in this case is producing steam that is nowhere near hot enough. A steam plant only gets up to reasonable efficiency when the hot end of the steam plant is at a very high temperature and pressure, which in this case would then react with the carbon element. Have a look at this - "The Mechanism of the Steam-Carbon Reaction" http://rspa.royalsocietypublishing.org/content/193/1034/377 http://rspa.royalsocietypublishing.org/content/193/1034/377
- msandford 12y ago
  Right, I'm well aware. But I was trying to be conservative as to how pessimistic we should be. We can always be more pessimistic, but we should be no less pessimistic than halving the efficiency. It's not a useful number except to show that on the back of the envelope it's not that great for power generation. The 85% case is probably more about desalinization than it is about making steam to do useful work unless that useful work is heating. A concentrator, some of this stuff and you could make solar powered steam kettles which are very common in large kitchens.
  - lotsofmangos 12y ago
    fair enough, is just that your calculation on power generation put it as being massively better than the best commercially available solar power, which struck me as wildly optimistic
    - msandford 12y ago
      It's only better until you figure in the costs to make it work. Nobody cares about actual efficiency, they care about dollars per watt. Even at 38% (which you can't get) there's no way it would be cheaper than PV because of all the infrastructure you'd need to concentrate sunlight and do all the piping, etc.
chr1 12y ago
Though you don't necessarily need to convert it to electricity, and can use the steam for something else, like desalination of sea water.
- waps 12y ago
  Nothing lasts in sea water. Least of all sponges. I doubt that's a practical application.
  - kordless 12y ago
    Just wash it off.
    - waps 12y ago
      Incidently, detergent is one of those things that won't work well in seawater. Plus seawater is corrosive. So even if you do manage to clean things, they're not as reusable as they otherwise would be.

lotsofmangos 12y ago

85% efficient at taking heat and using it to evaporate water isn't that high, they are not talking about thermodynamic cycles producing work. This doesn't look like something you would use to drive an engine with as for that you want the high temperatures that go with the high concentration of sunlight, as the amount of work you can get out is directly related to the relative distance of the hot and the cold end from 0K. edit: 0 - you must play the game 1 - you can never win 2 - you can only break even on a very cold day 3 - it never gets that cold