Comment by ebbv | Hacker News Reader

Comment by ebbv | Hacker News Reader

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No, it absolutely is not. Of all the ideas of how to power transportation in the future this is one of the worst.

First, the idea that it is carbon neutral is absurdly wrong. If you're pulling the carbon out of anywhere but the atmosphere (and you are), then it's no more carbon neutral than pumping oil out of the ground and burning that.

Second, it's hugely inefficient. If you're manufacturing fully synthetic petroleum, then that synthetic petroleum is acting like an energy storage medium, a liquid battery, rather than as a true fuel (a source where you're getting more energy out than you put in.)

Any kind of battery source which has to be physically moved around via other sources of transportation is hugely inefficient compared to EVs with actual batteries where the energy merely has to be sent down transmission lines and the like. The losses involved in moving electricity around are far, far less than moving synthetic petroleum or hydrogen or any other "pseudo battery".

Lastly, internal combustion engines are extremely inefficient themselves, especially compared with electric motors. They require tremendous upkeep and have energy losses that are three times that of EVs. So even if you could make the claim (which you can't) that your synthetic petroleum energy storage medium is 100% as efficient as moving power around, the ICE is going to result in needing to use up 3x as much energy to move your vehicle from Point A to Point B compared to an EV.

Synthetic petroleum is a really, really bad idea and should not be pursued.

I agree fully, synfuels are a hugely naive idea. However, I've been pondering the use of direct-ethanol fuel cells in the place of 'range extenders' that are currently on some EVs. Advantages are legion: ethanol has a ready (and in possibly sustainable) supply chain, ethanol is a liquid with comparable-if-low vapor pressure as gasoline, i.e. readily handled, ethanol is not hugely poisonous like methanol, has quite decent energy density, etc. Fuel cell conversion is acceptably efficient (compared to ICE anyway), so not that much fuel would be needed; most consumers would prefer to charge at home anyway, for cost reasons. The fuel cell would be used to back-up the battery, therefore it wouldn't have to be really large - it only needs to provide the mean load, not the peak load. And you'd never have 'range anxiety' again...

Disadvantages?

I shall address your points by paragraph:

1) Erm. There's only really two places you can get carbon - the ground, or the atmosphere. Any biofuel eventually comes from plants or algae, which get their carbon from the atmosphere. I don't really know where else you had in mind.

2) That doesn't make it inefficient. The whole point is that it's acting as storage rather than fuel. That's what makes it carbon-neutral - the carbon comes out of the atmosphere, then goes back (instead of out of the ground and into the atmosphere).

3) Not sure I buy that. Electricity distribution is hardly lossless (and what powers the power station?). Our best grid-scale storage solutions run about 75% efficient, while car-scale batteries leak charge much faster than a gasoline tank leaks gasoline. And both a gasoline car and an EV have to carry around heavy energy storage - the difference is the gasoline tank gets lighter as it empties.

4) To be fair, you have to compare the efficiency of the ICE to the combined efficiency of the motor, power station, and all intermediate storage (every time the power moves from one battery to another, you lose some, while gasoline can be stored and dispensed fairly losslessly). Transmission costs also have to compared like-for-like - grid scale distribution runs about 95% efficient, while oil tankers are 97-98% (though you have to factor in last-mile, and trucks are ten times as thirsty). I don't think the calculation is as clear-cut as you're making out.

It's also worth querying what exactly "efficiency" means. If the source is sustainable (and biofuel is), raw energy wastage is less important than gross environmental impact and safety. It's not clear to me that mining nuclear materials and dealing with the waste, or mining rare earth metals to carpet the land in solar panels, are necessarily better or more sustainable solutions that carpeting the land in fast-growing, high-energy crops and fuelling all of society that way. Perhaps it is a bad solution - it depends on how the numbers fall exactly on things like land use, (and possibly your values regarding safety decisions). If it's already been thoroughly analysed and found wanting, then I'd love to read that. But at the moment you've not really made an argument commensurate with the strength of your opinion.

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