3 ms·

The problem is energy conversion efficiency. Sure you can make synthetic jet fuel from solar panels, water and CO2 but the efficiency is miserable[1]. It's so

The problem is energy conversion efficiency. Sure you can make synthetic jet fuel from solar panels, water and CO2 but the efficiency is miserable[1]. It's something like 4% efficient and the metal catalysts sometimes aren't cheap. I guess it's important to start somewhere and work on efficiency improvements until it makes economic sense. [1]https://www.cell.com/joule/fulltext/S2542-4351(22)00286-0 https://www.cell.com/joule/fulltext/S2542-4351(22)00286-0

pfdietz 4y ago
The 4% efficiency is starting from sunlight. This overstates the case, because any solar scheme wastes most of it. That doesn't mean solar energy is impractical, any more than the roughly 1% conversion (if that) of sunlight to food calories in a farmer's field would make agriculture impractical. Also, that scheme is a thermochemical scheme for sunlight to hydrogen. Producing H2 gas by electrolysis driven by PV would be more efficient. It's a common nuclear talking point that solar is impractical because of efficiency. This is a bogus argument, since comparing efficiency of schemes that use different inputs is comparing apples and oranges. Sunlight is cheap and abundant and can be wasted without intolerable pain.
- cplusplusfellow 4y ago
  I mostly hear nuclear talking points of the fact that it’s a guaranteed GW/year production versus intermittent weather-dependent allocation.
  - pfdietz 4y ago
    As if various storage schemes to deal with that don't or can't exist.
    - pstrateman 4y ago
      Energy storage at scales necessary to buffer solar/wind at 100% of the grid do not exist.
      - pfdietz 4y ago
        Nor does nuclear at the scale necessary to power the world. Today's commercial reactors can't do it; breeding is needed. This would mean scaling up breeder reactors by roughly a factor of 1000. This is actually a larger scaleup than would be needed for storage, I believe. What, you're allowing nuclear to scale up, but not storage? Very high double standards you all have in Nuclearstan.
        narrator 4y ago
        Breeder reactors are such an overlooked technology. Only Russia and India are seriously pursuing them. The thing about breeder reactors is they can get rid of the nuclear waste problem and use 100x the energy of the input fuel vs conventional reactors. It's much more technically complicated, and the biggest ones are only 800 megawatts right now, but they could conceivably go much larger.
        Schroedingersat 4y ago
        How much Pu240 does the BN800 fission? How much does it produce? No breeder program has ever closed the fuel cycle, and the "closed" cycle doesn't even aspire to get rid of the fertile isotopes which will just be more high level waste. What reprocessing does do though is let out all the Kr, Cs, Tc, T and so on that was safely contained in your spent fuel bundle. Much of which is just vented or dumped in the ocean.
gumby 4y ago
How efficient is a leaf? Hoe is efficient is collecting and compressing algae for 40 million years?
_fizz_buzz_ 4y ago
The 4% efficiency number doesn't matter, because you get the sun light for free. What matters is how much such a system costs.
- gumby 4y ago
  Which is where efficiency matters since the cap ex amortization is divided by production.
SamBam 4y ago
As solar becomes cheaper and cheaper, low efficiencies may still be worth it. We're never going to power a 747 on solar, but if the energy in the fuel comes from the sun, even if 90% of that is "wasted," it's still greener.
mschuster91 4y ago
Doing the process with standard technology will always be a PITA, partially because catalytic agents tend to not just be expensive but primarily sourced from questionable or enemy nations. I think the eventual answer will be in genetically engineered microbes or plants, if only because it is easier to scale up vats with microbes and nature already has figured out synthesis paths for ages.

pfdietz 4y ago

The 4% efficiency is starting from sunlight. This overstates the case, because any solar scheme wastes most of it. That doesn't mean solar energy is impractical, any more than the roughly 1% conversion (if that) of sunlight to food calories in a farmer's field would make agriculture impractical. Also, that scheme is a thermochemical scheme for sunlight to hydrogen. Producing H2 gas by electrolysis driven by PV would be more efficient. It's a common nuclear talking point that solar is impractical because of efficiency. This is a bogus argument, since comparing efficiency of schemes that use different inputs is comparing apples and oranges. Sunlight is cheap and abundant and can be wasted without intolerable pain.

cplusplusfellow 4y ago
I mostly hear nuclear talking points of the fact that it’s a guaranteed GW/year production versus intermittent weather-dependent allocation.
- pfdietz 4y ago
  As if various storage schemes to deal with that don't or can't exist.
  - pstrateman 4y ago
    Energy storage at scales necessary to buffer solar/wind at 100% of the grid do not exist.
    - pfdietz 4y ago
      Nor does nuclear at the scale necessary to power the world. Today's commercial reactors can't do it; breeding is needed. This would mean scaling up breeder reactors by roughly a factor of 1000. This is actually a larger scaleup than would be needed for storage, I believe. What, you're allowing nuclear to scale up, but not storage? Very high double standards you all have in Nuclearstan.
      - narrator 4y ago
        Breeder reactors are such an overlooked technology. Only Russia and India are seriously pursuing them. The thing about breeder reactors is they can get rid of the nuclear waste problem and use 100x the energy of the input fuel vs conventional reactors. It's much more technically complicated, and the biggest ones are only 800 megawatts right now, but they could conceivably go much larger.
        Schroedingersat 4y ago
        How much Pu240 does the BN800 fission? How much does it produce? No breeder program has ever closed the fuel cycle, and the "closed" cycle doesn't even aspire to get rid of the fertile isotopes which will just be more high level waste. What reprocessing does do though is let out all the Kr, Cs, Tc, T and so on that was safely contained in your spent fuel bundle. Much of which is just vented or dumped in the ocean.

gumby 4y ago

How efficient is a leaf? Hoe is efficient is collecting and compressing algae for 40 million years?

_fizz_buzz_ 4y ago

The 4% efficiency number doesn't matter, because you get the sun light for free. What matters is how much such a system costs.

gumby 4y ago
Which is where efficiency matters since the cap ex amortization is divided by production.

SamBam 4y ago

As solar becomes cheaper and cheaper, low efficiencies may still be worth it. We're never going to power a 747 on solar, but if the energy in the fuel comes from the sun, even if 90% of that is "wasted," it's still greener.

mschuster91 4y ago

Doing the process with standard technology will always be a PITA, partially because catalytic agents tend to not just be expensive but primarily sourced from questionable or enemy nations. I think the eventual answer will be in genetically engineered microbes or plants, if only because it is easier to scale up vats with microbes and nature already has figured out synthesis paths for ages.