[archi42]

They say they need 77kWh to produce one gallon of fuel. Which has 33.7kWh of energy stored. Assuming 20% average efficiency of an ICE engine (from Wikipedia), so 6.74 kWh per gallon end up as actual "work" done by the engine.

A quick DDG search suggests BEV has an efficiency of 80%, so the same 77kWh would end up doing 61.6 kWh of actual work when charged directly.

IMHO long-term this is no solution for general transportation, but ICE cars are still sold and as such will stay around for a few decades. Plus applications which require a higher energy density (mainly aviation & space; probably trucking & shipping; maybe long-range personal transportation) could make good use of these.

[scotty79]

This has the benefit of creating incentive for capturing CO2 which is something we should be willing to pay for in coming decades.

[archi42]

That's a distraction: The extraction is only temporarily. The value of an amount of efuel is not in that it's made from captured CO2, it's in burning that efuel to drive some machine. So yeah, there will be some CO2 captured in storage and transit, but that's will be less than what we release every year.

If you want to capture CO2 for good: Capture it, dump it somewhere and don't touch it ever again. The trick is to derive (monetary) value from the permanent storage. Just digging a hole and dumping it there doesn't make anyone richer (only healthier, but who's paying for that on the necessary scale?). Thinking about it, maybe we can use it in construction?

[scotty79]

I think the only way to make capturing CO2 valuable is to tax the economy and pay for actually captured CO2 directly.

Fuel manufactured out of CO2 might be easily verifiable proof of capturing CO2.

[archi42]

Maybe we have a little misunderstanding here? If you produce fuel from CO2, that CO2 will be released again once that fuel is burned. It's CO2 neutral, not negative.

So assume today we have 100t CO2 in the air. You capture 20t of that and make efuel from it. Now we have 80t of CO2 in the air. Which is great. However you went through all the effort so you could actually sell that efuel instead of sitting on it. So lets say I buy it from you. And then I'll burn some in my car and use some to heat my house. As a result, we now have 100t of CO2 in the air, again.

Would I use fossil fuel and heating oil, then we would have 120t of CO2 in the air. So non-ironic hooray, we prevented that. We're neutral. But once we're upgrading me to an electric heat pump and an electric car that energetic detour won't be necessary anymore, since I can use the electricity directly. That's also much more efficient: The heat pump by a factor of 4 to 9 (77kWh produces 1 gal efuel, which burns for 33.7kWh of heat; 77kWh used in a heat pump produces 154 to 308kWh of heat), and the car by a factor of 10 (math given previously).

If the goal was to have 80t in the air on the other hand, then at least it didn't make it worse; but until we dump CO2 somewhere it isn't released into the air again, we will never get to that goal.

It's not like I'm anti-efuel; for a long time to come and for some specialty use cases it will be a good solution to not make things worse (e.g. space rockets), but in the general case: It's a stop-gap, not a solution.

//edit: What we could do is tax people who release CO2 for the subsequent, necessary capture. That can then be scrubbed from the air again using the 36$ process the people on the linked page claim to use/have invented. Use that CO2 in an efuel and release it again, you pay to have it scrubbed again. To reduce the total amount of CO2 in the air, require that you not only pay to scrub the emissions, but some additional % (until the problem is solved, then just pay to scrub what was actually emitted). That's essentially a simplified & more strict CO2 certificate trade.

[scotty79]

> It's CO2 neutral, not negative

Yes. But at the same time is displaced a product that would put out CO2 into the atmosphere. So you reduce the amount of CO2 that is being put out.

So while neutral, not negative, it initially has the same effect that a novel carbon negative activity might have that doesn't replace anything.

I agree with you that later orther solutions will be better.