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Why do transit agencies keep falling for the hydrogen bus myth?

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Re: Why do transit agencies keep falling for the hydrogen bus myth?

#81

Post by thfuran »

kittoes wrote: post #70
datadrivenangel wrote: post #56

Earlier quoted context omitted.

Regenerative breaking is not perfectly efficient, so you may loose a significant portion of the additional energy needed. Better EV systems are what, 70-80% efficient on the breaking efficiency?

Sure, but you lose 100% in the case of combustion...

Okay, but gasoline is far more energy dense than batteries and a gas tank is a whole lot cheaper than a battery pack, so vehicles can have a gas tank big enough that that doesn't cause range problems. I don't know about buses, but you can buy a pickup with a 48 gallon tank. Even after assuming only about 1/3 efficiency, that's still equivalent to some 500 KWhr, which is several times more than any consumer EV I'm aware of.

Re: Why do transit agencies keep falling for the hydrogen bus myth?

#82

Post by AnthonyMouse »

kittoes wrote: post #70
datadrivenangel wrote: post #56

Earlier quoted context omitted.

Regenerative breaking is not perfectly efficient, so you may loose a significant portion of the additional energy needed. Better EV systems are what, 70-80% efficient on the breaking efficiency?

Sure, but you lose 100% in the case of combustion...

That's efficiency, not range. Suppose hilly terrain reduces range by a third for electric vehicles and half for diesel. The diesel bus just fills up twice as often. The electric bus needs a 50% bigger battery in order to finish the same route without stopping to charge, and then it becomes 70% because it has to lug the bigger battery up the hills.

You can just... do that, but that doesn't mean it's not a thing you have to do, and it's not free.

Re: Why do transit agencies keep falling for the hydrogen bus myth?

#83

Post by andix »

Answer to the question: political reasons and lobbying.

Hydrogen is produced by the big oil and gas companies. By pushing hydrogen vehicle instead of battery electric vehicles they stay in business.

They market hydrogen as a green alternative to oil, although most hydrogen is currently produced from fossil sources, and this won't change soon (next 10 years).

Re: Why do transit agencies keep falling for the hydrogen bus myth?

#84

Post by mschuster91 »

WalterBright wrote: post #40
mschuster91 wrote: post #28

Earlier quoted context omitted.

> There is no known battery technology, or one on the horizon, that can provide a large enough power/weight to make them practical. Small aircraft are already there. I'm looking into starting my pilots license this year, the local flight school recently acquired an Elektra Trainer [1], that apparently has 2.5 hours worth of flight time [2]. Big transoceanic widebodies obviously will be fossil fuel based for a long ti…

It appears to be an ultra-light.

It is, because it's easier to get started with certification and experience in ultralights than in full-size planes. It won't be long until we see bush capable Cessnas, I think.

Re: Why do transit agencies keep falling for the hydrogen bus myth?

#85

Post by smolder »

adrian_b wrote: post #49
bobthepanda wrote: post #21

Earlier quoted context omitted.

This depends a lot on local climate and topography. Seattle has kind of been a bust with them because the hills really reduce the amount of charge, and on top of that the existing bus depots are already full, so switching to electric only would mean having to find and locate space for more bus depots, which is quite difficult.

Hills should never reduce the range, because the energy lost during climbing up is recovered when going downhill. This is one of the great advantages of electric vehicles with batteries, when properly designed. Electric buses with batteries are even more suitable for cities with hills than for cities without hills, because they provide greater energy savings over buses with ICEs. While I have never used buses with ba…

Regenerative braking is nice but as sibling pointed out it doesn't nearly recapture everything. Another factor is that the additional load whether accelerating up a hill or braking down one puts more current through the system. In fact nearly every part of the drivetrain will experience accelerated wear under those conditions, mechanical or electrical. Cooling systems, too. Properly spec'd, it's of course very doable, but it's true hilly terrain is more difficult.

Re: Why do transit agencies keep falling for the hydrogen bus myth?

#86

Post by thfuran »

bluGill wrote: post #66
abdullahkhalids wrote: post #47

Earlier quoted context omitted.

Many bus routes have a 5-10ish min break at some point (usually the main station) in the route. If you can utilize those ten minutes to do a top-up, you can go a lot further on the same sized battery.

No bus route should be more than 15 minutes between full and empty. That is you start at some station, go 15 minutes, then turn around and go back. There are many systems that attempt to do more, but there is no point: people have places to be: on the bus is not on that list. That 15 minutes means an average of 7 minutes, now they walk to some other express bus that gets them nonstop (at faster speeds) to someplace,…

Is there any bus route anywhere that never goes more than 15 minutes from the depot?

Re: Why do transit agencies keep falling for the hydrogen bus myth?

#87

Post by kstrauser »

hatthew wrote: post #55

> Fuel cell buses do produce sufficient waste heat, but here’s the problem: it’s exceptionally expensive heat. Every degree of warmth comes from hydrogen — a fuel that’s costly to produce, store, and transport. Unlike diesel, heating with hydrogen’s waste heat is technically easy but economically painful. Isn't waste heat pretty much free by definition?

Thanks, you beat me to it. While it is more expensive per watt, that's a sunk cost: you've already paid it when you were consuming the hydrogen to make the bus move.

Re: Why do transit agencies keep falling for the hydrogen bus myth?

#89

Post by smolder »

kittoes wrote: post #70
datadrivenangel wrote: post #56

Earlier quoted context omitted.

Regenerative breaking is not perfectly efficient, so you may loose a significant portion of the additional energy needed. Better EV systems are what, 70-80% efficient on the breaking efficiency?

Sure, but you lose 100% in the case of combustion...

Approximately 100% but not exactly, given that engine braking downhill drives the accessories without any fuel. (Alternator, aircon, pumps, etc.)

Re: Why do transit agencies keep falling for the hydrogen bus myth?

#90

Post by bolognafairy »

kittoes wrote: post #70
datadrivenangel wrote: post #56

Earlier quoted context omitted.

Regenerative breaking is not perfectly efficient, so you may loose a significant portion of the additional energy needed. Better EV systems are what, 70-80% efficient on the breaking efficiency?

Sure, but you lose 100% in the case of combustion...

Do you know which conversation you’re replying to?

The original point was: hills do not matter, because what goes up must come down, and regen will get all the energy back.

This is categorically untrue, at the very least because regen doesn’t capture at 100% efficiency. It being “more than ICE” doesn’t mean anything.

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