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Comment by robonerd | Hacker News Reader

From a CO2 perspective, synthetic fuels don't have an intrinsic advantage, unless you use biomass as your source of carbon. Traditionally, synthetic fuel has been made using coal or natural gas as the source of carbon. There is still some advantage to this, the nitrogen and sulfur content of the fuel can be dramatically reduced, which is great. But with regard to C02 specifically, you're basically burning coal. With biofuels, I think care needs to be taken to ensure we don't ruin the price of food for people by incentivizing farmers to grow fuel feedstock instead. Biofuels made from algae might be the best, since this wouldn't require the use of arable farmland.

Another approach is to pull the CO2 straight out of sea water. Apparently the US Navy thinks this might be a viable approach, since their nuclear aircraft carriers have power to spare.

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I believe when people say synthetic fuel they mean carbon neutral fuels that are made from renewable electricity.

The general idea is to use electrolysis to produce hydrogen, then combine that with atmospheric CO2 to produce methanol.

For instance: https://www.efuel-alliance.eu/efuels/what-are-efuels

Atmospheric carbon capture seems like an petroleum industry scam to me (check the 'Members' page of that website.) In principle it's what plants do, but plants do it using scale; there's a whole bunch of them. CO2 is under 500ppm in our air, and air isn't particularly dense in the first place; the amount of air you'd need to move through your capture plant is immense.

On the Costs & Outlook page of this site, they list their potential feedstocks; it's all biomass, except for the 'Technical Potential "Unlimited"' column, which mentions Power-to-Liquids. But how does that actually work and does it actually make sense?

Related parody of carbon capture: https://www.youtube.com/watch?v=MSZgoFyuHC8

It is possible, it’s just expensive.

The U.S. navy is interested in a fuel synthesizer that works on co2, seawater and uranium and they can pay more than you per gallon because you don’t have to refuel an aircraft carrier in a war zone.

I fully agree with the bit about atmospheric carbon capture. What a pointless waste of energy. But if you start thinking of plant biomass not as the energy source, but just as the carbon provider for making carbohydrates from your hydrogen, then energy crops vs food crops conflict suddenly disappears, because the nutritious parts usually come alongside plenty of lower energy "plant waste" that should be good enough as a carbon provider for hydrogen "carbonation". Certainly much better for the task than atmospheric CO2. And all that plant carbon would soon continue it's cycle as atmospheric CO2 anyways, so it's just as good as atmospheric capture.

Obviously in the present context "synthetic" refers to fuel produced using renewable energy. If you are willing to use petroleum, you don't need to synthesize anything because that is where you started, unless maybe you are turning NG into kerosene. But that would be a dead end technology, so would not return investment.

Energetically, the principal synthetic fuels will be anhydrous ammonia and hydrogen. Capturing CO2 to make methane and kerosene is possible but more expensive. In particular, you need hydrogen as input, and must both capture and crack the CO2.

But for some uses you still need hydrocarbons, at least for now. Given carbon taxes subsidizing synthetics, the synthetics could be competitive.

In the longer term, aviation does much better with liquid hydrogen fuel, but it takes new airframes or, at least, extensive retrofits.

I recently commented about synthetic jet fuel in another thread https://news.ycombinator.com/item?id=31704829:

> A problem with biofuel is scaling it up, see: https://ieeexplore.ieee.org/document/7498153. According to that article the U.S. would need to devote "an area bigger than Texas and California and Pennsylvania combined" to crops specifically for its own jet biofuel needs. That's just for flying, not for food or fuel for ground transportation or anything else.

Also that article says that from 2009-2013 a $100 million effort was made to figure out how to get sufficient synthetic fuel from algae but they eventually gave up and went back to the drawing board.

Biofuel is an obvious dead end.

The future has no place for biofuel in any substantial amount.

Ethanol made from food (like corn) is a dead end.

Firewood and derivatives have always had an important place in heating and cooking, and are likely to continue in that role for a while. Other types of biomass based hard fuels (from recycled garbage/waste, algae, etc) will most likely also play a role in electricity production and heating, but perhaps a small one (unless algae based biomass takes off).

And for liquid fuels for transportation use, algae may also end up being a competitor to hydrogen when oil runs out. I remember there were a lot of companies working in that space 10 years ago, but then there was the oil price crash in 2015, and it seems many switched away.

For instance algenol was positioning itself as a fuel company, but appear to have diversified:

https://www.algenol.com/sustainable-products/?category=ndust...

If oil prices remain at current levels, though, algae may be only a few years away from scaling up to take a significant part of the market.

Firewood does not constitute a "substantial amount", by any industrial measure. It will continue being used, in decreasing amounts as very cheap efficient stove designs gradually penetrate the tropics.

Growing algae occupies >10x the area of floating solar panels producing the same usable energy. Harvesting and processing algae costs >>1 orders of magnitude more than delivering electrical power via wire.

The reasonable expectation is that transitions will be toward cheaper alternatives, with societal inertia acting to delay transition well beyond the point of obvious benefit. Thus, existing nukes will continue operating well after building solar + storage and then switching to that would be cheaper.

In Norway, biofuel (mostly firewood) accounts for a bit more energy used than coal and a little less than natural gas:

https://www.nve.no/Media/7326/energibruk_energivar_2014-kopi...

Here is similar data from Sweden:

https://www.researchgate.net/profile/Egnell-Gustaf/publicati...

Here is for the world, my understanding is that "Traditional Biomass" is mostly firewood there too:

https://ourworldindata.org/exports/global-energy-substitutio...

I keep thinking the direction kitchens are headed in developing countries is a solar powered microwave, induction cooktop, and fridge.

Does the lady of the house want to collect scraps of firewood and then cook in a hot already smokey kitchen or on a only heats the pan induction cooktop? Yeah.

The bottom billion people have no counter to put a microwave on. A solar panel, battery, microwave, induction cooktop, and fridge would cost several years' income preferentially spent (e.g) eating.

Getting together $10 for a stove that needs 5x less firewood is a challenge. They need a new one every year because making one that lasts costs more.

Can we allow CO2 emissions if we can sequestrate it somewhere else? Synthetic fuels sounds like a good idea.

It's capturing energy in point A and being used at point B. You can't just look at point B and yell "CO2 emissions!".

> if we can sequestrate it somewhere else?

That seems to be the big if.

https://en.wikipedia.org/wiki/Carbon_sequestration

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