Ultracapacitor Bus Recharges at Each Stop | Hacker News Reader

Ultracapacitor Bus Recharges at Each Stop

technologyreview.com

34 pointsnaish19 comments

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A capacitor can discharge at least as fast as it can charge. Let's see what remains after the first wreck.

The ultracapacitors store 5.9 KWH. (From the manufacturer's specs: http://www.sinautecus.com/products.html)

5.9 kilowatt-hour = (5.9 kW)(1 hour) = (5900 J/s)(3600 s) = 21.24 MJ.

A stick of dynamite contains roughly 2.1 MJ.

Welcome aboard!

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.

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.

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

To be fair, gasoline has over 30MJ/L - so a 20 gallon gas tank has well over 2,000 MJ of energy stored.

Gasoline != capacitor.

Find out what it takes to make a tank of gas explode. For a capacitor, all you need is a short (not necessarily between the terminals, either. Anything which breaches the dielectric - like mechanical impact - will do.)

Ultracaps don't discharge instantly, though. That parasitic inductance is actually one of their disadvantages vs. traditional plate capacitors, or even electrolytics.

If you short one, you get a melt/vaporization failure and a bit mess. You don't get an explosion.

It is an elegant idea, but I am not sure it could reach wide adoption. Basically, the pitch is that over its lifetime, it will be cost efficient when compared to current alternatives. However, everyone thinks that near-term alternatives -- including those that include advanced ultra-capacitors -- will be even better so they wait.

I did really like the article saying The buses can also capture energy from braking, and the company says that recharging stations can be equipped with solar panels (although this is mainly to further the perception that the vehicles have a lower carbon footprint). It always bothers me that green concepts try to create an amalgamation of 50 different green sources. Carry over the Unix philosophy, please.

Since there's no one green energy source that will cover our entire energy need, a mix is required.

Putting up a solar panel just because it looks good is contra-productive, however, as it makes the entire green energy movement look less than serious.

[edit: rephrased a tiny bit]

Um, doesn't having 50 different devices to convert X into electricity, then piping all of them to a storage device actually match the Unix philosophy perfectly?

I should have been more precise. I was referring to the solar panels at bus stops, not the regenerative breaking technologies.

That's a really clever idea. Ultra-capacitors are by themselves a very neat technology, this kind of ingenuity in the transportation industry is a small step in the direction of letting go of the oil addiction, sooner is better in my opinion.

The way the system is described it has clearly been engineered to maximize cost savings, but I don't think the passenger will be too happy with a bus that stops for several minutes every couple of stops. Better to do that charging in smaller gulps at every stop, it will cost more (because you need more charging stations) but the public will be much more accepting of a technology that does not right away contain a very visible drawback.

So what you're saying is that if my bus is stuck in stop-and-go traffic for too long I will have to get out and push?

Hmm so I'll be going on a bus and it will every couple of miles stop for a few minutes to charge? I guess I will stick with trams and trolleybuses.

What they're trying to do is have it recharge a little bit at every bus stop, and from braking.

Basically the exact same ride experience as you have now.

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