Climate change will not bring about our end, but this will--

Yeah, I kinda agree with Imaginos there.

But it's a damn good start.



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Imaginos1892 wrote:

chuckpeterson wrote:“We think this is very scalable and will have world-wide markets,” says Oldham. “All you need is air and water as feedstocks, and some electricity.”

Aaaah, make that a shitload of electricity. Gasoline contains about 37 KWH of chemical energy per gallon. Nothing is ever 100% efficient, so it will take a lot more than 37 KWH of electricity to make one gallon of ‘carbon-free’ gasoline.

And then, when you burn it in an internal combustion piston engine, you will get less than 6 KWH of usable energy out of it.

You’d be an order of magnitude better off using that electricity to charge electric cars.

I can see some use-cases for it though where electric propulsion doesn't cut it and you don't have easy access to hydrocarbons.

Also, didn't Zubrin talk about a process that takes CO2 and produce fuel in his book The Case for Mars?

Imaginos1892 wrote:

chuckpeterson wrote:“We think this is very scalable and will have world-wide markets,” says Oldham. “All you need is air and water as feedstocks, and some electricity.”

Aaaah, make that a shitload of electricity. Gasoline contains about 37 KWH of chemical energy per gallon. Nothing is ever 100% efficient, so it will take a lot more than 37 KWH of electricity to make one gallon of ‘carbon-free’ gasoline.

And then, when you burn it in an internal combustion piston engine, you will get less than 6 KWH of usable energy out of it.

You’d be an order of magnitude better off using that electricity to charge electric cars.

However, for long range airplane travel, batteries need another order of magnitude improvement (at least) in energy density to be competitive with hydrocarbons.

Robert_A_Woodward wrote:However, for long range airplane travel, batteries need another order of magnitude improvement (at least) in energy density to be competitive with hydrocarbons.

You're right, airplanes are one application that pretty much requires liquid fuel. Batteries for motive power in airplanes will make no sense until somebody invents the Shipstone.

And, most airplanes use turbine engines, which do not suck nearly as bad as piston engines. We should have dumped piston engines on the Really Bad Ideas pile fifty years ago.

I'm writing a story which includes a solar-powered zeppelin that charges batteries to run at night, but enough batteries to run all night at full speed would take up more of the zeppelin's gross lift capacity than I wanted to allocate. They've got about a quarter of that. There are also a pair of very high-bypass turbofan engines for auxiliary power, but they're limited by fuel capacity.

Another issue — how much energy do they need to harvest carbon dioxide from air that only contains about 0.04%, or substantially less if you're near a lot of plants in the daytime? Electrolyzing water is not very efficient, either.

You'd be much better off to grow corn or soybeans and squeeze them for oil. A jet engine can run quite well on vegetable oil.
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Relax, Charlie; I've got an ANgle!

Imaginos1892 wrote:..snip..
You'd be much better off to grow corn or soybeans and squeeze them for oil. A jet engine can run quite well on vegetable oil.

The timescales and acreage involved presents some other challenges instead. On one hand you have a quite compact device that converts electrical energy to chemical energy with an efficiency that's not optimal, on the other hand you can produce fuel from growing crops which is not a compact operation plus the timescales in comparison is extreme for producing the same amount - but the energy is free.

Dunno how they would rank if we consider all three variables: Time / Efficiency / Compactness (which maybe also can be described as how mobile the operation is).

That's a complex one.

Biodiesel comes in arount the $1.80 per gallon more expensive than regular diesel. In the US at least.

But, the oil to make biodiesel is essentially a by product of making soy meal that is used for animal feed, and the soy meal market is driving soy production.

So really they just need to get the production costs down for converting soy oil to biodiesel.

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Annachie wrote:That's a complex one.

Biodiesel comes in arount the $1.80 per gallon more expensive than regular diesel. In the US at least.

But, the oil to make biodiesel is essentially a by product of making soy meal that is used for animal feed, and the soy meal market is driving soy production.

So really they just need to get the production costs down for converting soy oil to biodiesel.

I did a quick calculation on the conversion factor for rapeseed (which is much better source of oil than soy) to biodiesel long ago, for a normal yield - 1 ha converts into about 1300 liters (~343 gal) of biodiesel using acid cycle conversion. The same for soy is 446 liters.

Anyway, producing biofuel from crops has its own share of problems, from mono-culture growing to the need to balance it against the need for food.

Imaginos1892 wrote:

Robert_A_Woodward wrote:However, for long range airplane travel, batteries need another order of magnitude improvement (at least) in energy density to be competitive with hydrocarbons.

You're right, airplanes are one application that pretty much requires liquid fuel. Batteries for motive power in airplanes will make no sense until somebody invents the Shipstone.

And, most airplanes use turbine engines, which do not suck nearly as bad as piston engines. We should have dumped piston engines on the Really Bad Ideas pile fifty years ago.

I'm writing a story which includes a solar-powered zeppelin that charges batteries to run at night, but enough batteries to run all night at full speed would take up more of the zeppelin's gross lift capacity than I wanted to allocate. They've got about a quarter of that. There are also a pair of very high-bypass turbofan engines for auxiliary power, but they're limited by fuel capacity.

Another issue — how much energy do they need to harvest carbon dioxide from air that only contains about 0.04%, or substantially less if you're near a lot of plants in the daytime? Electrolyzing water is not very efficient, either.

You'd be much better off to grow corn or soybeans and squeeze them for oil. A jet engine can run quite well on vegetable oil.
———————————
Relax, Charlie; I've got an ANgle!

Niven and Pournelle beat you to it.

Joat42 wrote:

Annachie wrote:That's a complex one.

Biodiesel comes in arount the $1.80 per gallon more expensive than regular diesel. In the US at least.

But, the oil to make biodiesel is essentially a by product of making soy meal that is used for animal feed, and the soy meal market is driving soy production.

So really they just need to get the production costs down for converting soy oil to biodiesel.

I did a quick calculation on the conversion factor for rapeseed (which is much better source of oil than soy) to biodiesel long ago, for a normal yield - 1 ha converts into about 1300 liters (~343 gal) of biodiesel using acid cycle conversion. The same for soy is 446 liters.

Anyway, producing biofuel from crops has its own share of problems, from mono-culture growing to the need to balance it against the need for food.

But it is just so deliciously evil to burn Africa and Asia's food for Europe's fuel.

TFLYTSNBN wrote:But it is just so deliciously evil to burn Africa and Asia's food for Europe's fuel.

Citation needed.