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Comment by neltnerb | Hacker News Reader

So for context -- I was working on this ten years ago. I don't have much to say about this particular example other than to note that almost all ammonia today is made using natural gas as the hydrogen source.

Using ammonia is a neat idea, if made renewably, but it will continue to be a challenge to use in cars because it is pressurized, corrosive, and toxic even compared to gasoline.

Obviously the bigger market for renewable ammonia should be fertilizers because right now we're feeding our crops petrochemicals in order to get high enough yields to feed us. That seems like a bad situation to put yourself in if there's any other choice.

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It's technologically trivial to make renewable hydrogen from clean electricity and non-potable water, under the right economic incentives (Carbon tax)

Indeed.

I would put "making transportation fuels" at about the bottom of the list in terms of the best use of electricity until such time as all electricity is renewable.

It just doesn't make sense until the entire grid or close to it is renewable already because if you use 1J of electricity to make 0.95J of hydrogen that gets turned into 0.9J of ammonia you'd have been way better off just using 0.9J of gasoline in the first place because that 1J of electricity probably was generated from 3J of fossil fuels.

So I'd say the same regarding fertilizers -- I'd rather they didn't use natural gas as a hydrogen feedstock, but generating hydrogen from electricity generated at a natural gas plant is a very Rube Goldbergy way to generate ammonia that still uses natural gas.

That's changing, but it's nowhere near true yet. Generating ammonia from excess renewable electricity that the grid can't sink does make more sense to me.

I'm not sure I'd agree about ordering. Solar power seems to be getting cheaper faster than batteries are. We might be in the position in the not too distant future where we have more electricity during sunny days than we know what to do with but still need some natural gas power plants to get us through cloudy months. Depending on capital costs "make H while the sun shines" might be a reasonable business.

Yeah, I am also on board with diverting excess electricity into transportation fuels if it literally can't fit on the grid.

But every joule of electricity generated from renewables that makes it to the grid is a joule of electricity that wasn't generated with petrochemicals at the moment because natural gas peaker plants are still a thing.

I had to once write a grant proposal for essentially the kind of thing you're talking about. It's exceptionally hard to make a good overall systems efficiency case for taking electricity and turning it back into fuels. I hope you agree that displacement of petrochemical electricity sources is far preferable to generating chemicals as a byproduct if the grid does have room for more electrons.

The only way I was able to find to make it work economically was to take excess electricity and convert it into fairly high value chemicals -- but even there, just turning petrochemicals into those same chemicals would in almost every case be more efficient.

I look forward to the day when we have so much renewable generation that we have no petrochemical electric plants left to displace. Hopefully it is not too far off, I like your optimism about solar and agree it may be warranted.

The spot price of electricity has gone negative in certain times and places. So power from then could potentially have not have been generated from petrochemicals (though, it might have been from a oil or coal fired steam plant).

If we could change the natural gas peaker plants to ammonia powered peaker plants, we could also use plants that are more base-load(nuclear), and use the ammonia as a long term power storage.

With 80%-90% losses -- Haber-Bosch is inefficient and so is combustion. I just have a hard time picturing that beating batteries. If it made a high value chemical maybe economically, but not on a purely energy basis, the efficiencies just can't add up.

Haber-Bosch requires compression to ~100bar or greater to see much of any conversion and has something like 15% yield per cycle. It is not pretty.

I find it impossible to imagine transitioning engines and fueling stations to ammonia before we get batteries light and reliable enough to meet the majority of people's needs. We put many power plants worth of petrochemicals into ammonia right now, replacing it would be great but it just doesn't seem like a low fruit to grab at.

What I think is a lot of this is put out there as an attempt sideline workable technologies to keep the fossil fuel party going. 'Clean coal' 'Carbon Capture' 'Next Generation Reactors' 'Hydrogen economy' all unworkable trash.

I agree, I won't name and shame but the grant I was working on was clearly funded by some coal lobby or something because the premise was desperate on the face of it.

I practically said "this won't work efficiently, you should just not burn the coal" because nothing else could be justified energetically even if it was maybe economical. I tried my best but I can't change thermodynamics.

You can also make it with natural gas and capture the CO2 produced.

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