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Comment by proee | Hacker News Reader

Maybe you could create something similar to an airbag sensor, but instead of having it deploy an airbag it could dump all the charge in the caps into a resistive load (or maybe a one-time discharge load of some kind). It's certainly an easier problem to contain then say a tank of hydrogen.

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Agreed, especially considering a tank of liquid hydrogen is a major risk for a BLEVE, same with LPG vehicles. It strikes me as absurd that alternate fuel proposals will actually make our roads considerably more dangerous.

Instead of turning a vehicle crash into a wreckage with a potential for a fire, we'll be turning a crash into a wreckage with the potential for a massive explosion. Any passenger caught in a vehicle with a hydrogen fuel tank that BLEVE's is guaranteed to be dead, and so is anyone within yards of it. Our highways will potentially be more dangerous than a fire in a welding supply store.

Which would cause all of the energy to be dissipated as heat in an instant... perhaps you could put it into some non-volatile heat sink, but unless it's a really big heatsink, you wouldn't want to be anywhere near that thing when it went into resistor mode, especially if the energy density/storage of these caps increases. Maybe put it into a heatsink that's within a big vacuum thermos... :-)

Regardless, it's definitely easier to deal with than a tank of hydrogen, but I'd say that tech is a non-starter anyway. If we can make electricity alone work via advances in charging time over batteries and energy density over existing caps, there's really no reason to transport energy around in an intermediary, let alone an extremely inefficient and volatile one like hydrogen. Power mains are a much better solution, relatively lossless by comparison to an intermediary transform.

On the other hand, for action movies of the future, hydrogen tanker trucks would provide great explosion fodder :-)

> perhaps you could put it into some non-volatile heat sink, but unless it's a really big heatsink, you wouldn't want to be anywhere near that thing when it went into resistor mode

Specific heat capacity of water ~= 4(KJ per Kg per Kelvin)

so, assuming we can safely take water from 20 degC to 90decC, we'd need 21MJ / 4KJ/K/degC / 70degC == 75Kg of water as a heatsink.

Or about the weight of one passenger.

Double or triple up for safety factors (avoid steam) and you're still OK. Have some insulation and drive some A/C to chill the water further and you're also OK.

So yes, dump it into a resistive load immersed in a tank of water?

(Edit, that said I do think that The Right Way to do transport+energy etc is for us to find our correct "limitless" source of energy (fusion or orbital solar, I guess) and turn that into synthetic hydrocarbons as a convenient, relatively safe, energy dense fuel. i.e. we don't build massive supergrids for pushing that power to people over wires. We pump the power into a CO2+H2O=>petrol converter which we then ship around the world using the existing infrastructure. We also don't need to retool the whole world's transport infrastructure. Obviously all carbon-neutral too. (Carbon -ve if you've got the spare power.))

How would systems running on petrol be carbon-neutral? Granted, you reduce one form of carbon emissions by presuming a clean form of energy and petrol generation. Use of the petrol, however, should still result in carbon emissions. Have I missed something?

If you're making the hydrocarbons from CO2 and H2O, you're taking as much CO2 from the air as burning the hydrocarbons will liberate.

Obviously, you need to put in the energy too. But I think synthetic hydrocarbons are a great way to carry around useful energy. They're very energy-dense, should be cleaner than oil from the ground and the whole world is tooled up to use them.

However, they're not useful until we also have:

- loads of power

- an efficient way of turning that power + CO2 + H2O into hydrocarbons

One could try such a thing (patterned after the emergency quenching circuit found in MRI machines) but there is no indication that these buses (or other proposed ones) include such a feature.

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