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Comment by snek_case | Hacker News Reader

80% isn't amazing, it's not ideal for an electric car, but it's not terrible either. IMO, to switch to 100% renewables, we're going to need grid-scale batteries, but it might also help if we had a mechanism to achieve seasonal energy storage.

I know hydrogen is hard to store, so I think it would be best if we could somehow use electricity to produce ethanol directly from CO2 and water (is that feasible with reasonable efficiency?). But just imagine if we could, in the summer, we could turn excess solar power into ethanol and stockpile it for the winter. We could also use that fuel to power jet airplanes and cargo ships without using any fossil fuels.

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CO2 to hydrocarbon fuels (not ethanol, but methane and potentially liquid hydrocarbons as well) is exactly what Terraform Industries is planning to do.

https://terraformindustries.com/

Do you know what kind of efficiencies they get and how close to practical or not this is?

I’ve always worried about the energy density of batteries. They’re explosive enough as it is, imagine if it was 10x worse. I’ve always hoped that we’d transition to synthetic fuel - fuel like diesel is surprisingly stable and safe.

the batteries explode because of the materials in them, not because of the stored electrical energy. An full lithium battery wouldn't explode much more violently than an empty one.

I fly FPV so I deal with exploding batteries from time to time. Fully charged batteries explode much more violently than discharged batteries which tend to smolder instead. I suspect the additional electric discharge is adding ‘fuel to the fire.’

Interestingly, a discharged lithium ion battery still has electric potential in it, it's just that we stop discharging it after it hits a cutoff voltage to protect the battery's lifespan.

I wonder if a truly 100% discharged battery (down to zero volts) would actually be basically inert, and not even smolder if you poked it.

Lithium Ion batteries do burn much more readily when fully charged than when discharged -- this is because they self-discharge rapidly at elevated temperatures, which provokes an even greater reaction of the materials inside of them. Specifically, if the cathode of NMC/NCA batteries gets hot enough, it will decompose into oxygen and really kick off the graphite + electrolye burning. Discharged batteries are tougher to get to burn since it's harder to heat the cathode to that point externally so oxygen has to come from the environment.

This is not correct and is against basic thermodynamics and conservation of energy. Store a whole bunch of potential energy somewhere and you have an explosive. The more stored energy of any form, the bigger the boom.

Fuel infrastructure burns all the time, though. It's like every month there's a video of some tanker overturned on the highway, or a refinery fire, or a gas explosion. I don't have statistics in front of me but I'm all but certain that lithium batteries as deployed today are safer by pretty much any metric you want to pick.

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