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Maybe I am naive, but let's say that using liquid hydrogen instead of synthetic kerosene would use 1/3 of the input energy. OK. To me, it seems way more feasibl

Maybe I am naive, but let's say that using liquid hydrogen instead of synthetic kerosene would use 1/3 of the input energy. OK. To me, it seems way more feasible to triple the amount of input energy capacity (build more solar, wind, nuclear, ...whatever), than to completely redesign aviation around a fuel with such unforgiving constraints. What am I missing?

credit_guy 3y ago
You're not missing anything. What everyone else is missing is that to achieve net zero you don't need to decarbonize everything. The planet absorbs about half of the CO2 that we emit (see the IPCC FAQ 5.1 [1]). If we decarbonize everything but aviation we are well into negative CO2 emissions territory. [1] https://www.ipcc.ch/report/ar6/wg1/downloads/faqs/IPCC_AR6_WGI_FAQ_Chapter_05.pdf https://www.ipcc.ch/report/ar6/wg1/downloads/faqs/IPCC_AR6_W...
mdorazio 3y ago
Perhaps that traditional engines shoot greenhouse gas straight into the stratosphere and that’s a bad thing?
- goethes_kind 3y ago
  I was talking about carbon neutral synthetic kerosene which is a step beyond green hydrogen in the power-to-gas pipeline.
  - mdorazio 3y ago
    Not sure how I was supposed to get that from your comment or why you think kerosene is a better solution when burning it in jet engines still puts greenhouse gas straight into the atmosphere? I feel like I missed some big piece of your argument here.
    - qfiard 3y ago
      Synthetic kerosene was the hint. You can make carbon neutral kerosene in the same way as biofuel, it doesn't add greenhouse gases to the atmosphere since the carbon it contains was captured from the atmosphere. Not a perfect solution as it doesn't solve the impact of contrails and there is the problem of how to generate so much biofuel, but it is a valid way to decarbonize flying.
gene-h 3y ago
This study[0] claims that is not viable as it would require 9% of forecast renewable production in 2050. Less net carbon emission can be produced if the electricity is used instead to displace coal plants and the plane run on conventional kerosene. Building lots of nuclear power, which isn't as capacity restricted as photovoltaics, wind, and other forms of power the authors consider renewable in the study. Hydrogen would still require quite a bit of energy to produce, but if it can be used in fuel cells, it can potentially be more efficient than if burnt in a heat engine. This is a pretty big if for air travel as fast as current jetliners. Fuel cell power per unit weight would need to be drastically increased. [0]https://www.sciencedirect.com/science/article/pii/S0048969723025044 https://www.sciencedirect.com/science/article/pii/S004896972...
- coryrc 3y ago
  Renewables often generate power when it isn't needed. High efficiency reduces costs, but we're already wasting power and it gets progressively worse as the renewable share increases.
  - lowbloodsugar 3y ago
    Batteries are now improving in efficiency, cost, and availability of materials. This is driven by solar.

credit_guy 3y ago

You're not missing anything. What everyone else is missing is that to achieve net zero you don't need to decarbonize everything. The planet absorbs about half of the CO2 that we emit (see the IPCC FAQ 5.1 [1]). If we decarbonize everything but aviation we are well into negative CO2 emissions territory. [1] https://www.ipcc.ch/report/ar6/wg1/downloads/faqs/IPCC_AR6_WGI_FAQ_Chapter_05.pdf https://www.ipcc.ch/report/ar6/wg1/downloads/faqs/IPCC_AR6_W...

mdorazio 3y ago

Perhaps that traditional engines shoot greenhouse gas straight into the stratosphere and that’s a bad thing?

goethes_kind 3y ago
I was talking about carbon neutral synthetic kerosene which is a step beyond green hydrogen in the power-to-gas pipeline.
- mdorazio 3y ago
  Not sure how I was supposed to get that from your comment or why you think kerosene is a better solution when burning it in jet engines still puts greenhouse gas straight into the atmosphere? I feel like I missed some big piece of your argument here.
  - qfiard 3y ago
    Synthetic kerosene was the hint. You can make carbon neutral kerosene in the same way as biofuel, it doesn't add greenhouse gases to the atmosphere since the carbon it contains was captured from the atmosphere. Not a perfect solution as it doesn't solve the impact of contrails and there is the problem of how to generate so much biofuel, but it is a valid way to decarbonize flying.

gene-h 3y ago

This study[0] claims that is not viable as it would require 9% of forecast renewable production in 2050. Less net carbon emission can be produced if the electricity is used instead to displace coal plants and the plane run on conventional kerosene. Building lots of nuclear power, which isn't as capacity restricted as photovoltaics, wind, and other forms of power the authors consider renewable in the study. Hydrogen would still require quite a bit of energy to produce, but if it can be used in fuel cells, it can potentially be more efficient than if burnt in a heat engine. This is a pretty big if for air travel as fast as current jetliners. Fuel cell power per unit weight would need to be drastically increased. [0]https://www.sciencedirect.com/science/article/pii/S0048969723025044 https://www.sciencedirect.com/science/article/pii/S004896972...

coryrc 3y ago
Renewables often generate power when it isn't needed. High efficiency reduces costs, but we're already wasting power and it gets progressively worse as the renewable share increases.
- lowbloodsugar 3y ago
  Batteries are now improving in efficiency, cost, and availability of materials. This is driven by solar.