3 ms·

> The big question in my mind is whether direct air capture is inherently expensive Have a look at a tree... I suppose it's possible that billon years of evol

by e12e 6y ago

> The big question in my mind is whether direct air capture is inherently expensive Have a look at a tree... I suppose it's possible that billon years of evolution has ended on a local optimum for low energy input (direct sunlight), and we might revolutionize it with high energy (eg: high voltage electricity, fusion etc) - but I doubt it.

danans 6y ago
> low energy input (direct sunlight) Direct sunlight is actually quite powerful, around 1kW/m^2 at sea level. Although I'd guess most trees aren't particularly efficient at absorbing CO2 vs the energy they consume, which makes sense, since they only have to be as efficient as necessary to survive.
- ncmncm 6y ago
  2% efficient, at best. 1000J in, 20J worth of wood and leaves out. Burning it, you get back only a fraction of that, with much of it carried away in the smoke.
  - danans 6y ago
    That sounds about right. It takes a whole lot of energy to reverse entropy at the margins. Then again life exists basically at the margins of the massive energy output of the sun. But still, I'm not holding out that any such human created sunlight to chemical energy storage process is going to best the 20% conversion efficiency of solar panels * 95% round trip efficiency of modern batteries any time soon. I know there are companies trying to make synthetic fuels from atmospheric C02 + renewable electricity for very specific use cases that are challenging for batteries (i.e aviation) but the jury is still out on whether that will work at scale.
    - ncmncm 6y ago
      I here predict that there will not be any producers of fuel from atmospheric CO2. The prices of extracted petroleum and CH4 will plummet as carbon taxes increase and demand decreases, until only the absolute cheapest extractors remain, and those products will be used only where the carbon tax can be afforded: mainly aircraft, and then only until the much more cost-effective LH2-powered airframes ground them. (Those will be fueled with LH2 generated on the spot at airports using regional solar.) Solar-powered CO2 capture projects will bid for carbon tax credits. Only the cheapest processes will win bids, so will not produce fuel. Probably they will blow it underground, in places where the ground is porous, and let it react with rocks down there. Turning it into fuel and selling it will not qualify as reclaiming, because the carbon doesn't stay claimed.

by e12e 6y ago

danans 6y ago

> low energy input (direct sunlight) Direct sunlight is actually quite powerful, around 1kW/m^2 at sea level. Although I'd guess most trees aren't particularly efficient at absorbing CO2 vs the energy they consume, which makes sense, since they only have to be as efficient as necessary to survive.

ncmncm 6y ago
2% efficient, at best. 1000J in, 20J worth of wood and leaves out. Burning it, you get back only a fraction of that, with much of it carried away in the smoke.
- danans 6y ago
  That sounds about right. It takes a whole lot of energy to reverse entropy at the margins. Then again life exists basically at the margins of the massive energy output of the sun. But still, I'm not holding out that any such human created sunlight to chemical energy storage process is going to best the 20% conversion efficiency of solar panels * 95% round trip efficiency of modern batteries any time soon. I know there are companies trying to make synthetic fuels from atmospheric C02 + renewable electricity for very specific use cases that are challenging for batteries (i.e aviation) but the jury is still out on whether that will work at scale.
  - ncmncm 6y ago
    I here predict that there will not be any producers of fuel from atmospheric CO2. The prices of extracted petroleum and CH4 will plummet as carbon taxes increase and demand decreases, until only the absolute cheapest extractors remain, and those products will be used only where the carbon tax can be afforded: mainly aircraft, and then only until the much more cost-effective LH2-powered airframes ground them. (Those will be fueled with LH2 generated on the spot at airports using regional solar.) Solar-powered CO2 capture projects will bid for carbon tax credits. Only the cheapest processes will win bids, so will not produce fuel. Probably they will blow it underground, in places where the ground is porous, and let it react with rocks down there. Turning it into fuel and selling it will not qualify as reclaiming, because the carbon doesn't stay claimed.