# Is the Hummer "greener" than the Prius?

Eeyore wrote:

From my other post, you need at least 530ish mJ/kg or 150ish kWh/kg to be competitive with gasoline. So, in other words, 1.5 kWh/kg is two orders of magnitude away from being "suitable."
nate
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And the real figure for NiMH is nowhere near 1500Wh/kg anyway. By another order of magnitude
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"Matthew T. Russotto" wrote:

You don't need 1500Wh/kg to make a hybrid EV feasible. Jeez. That would give it ~ 500 miles range without a recharge or even running the ICE !
Graham
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Eeyore wrote:

You'd need more than that for your "city car" serial-sometimes-hybrid to be practical, at least here in the YooEss. People expect a 4-500 mile range per "gas tank" of whatever sort. I don't see where you are getting your figures from, however - let's do the numbers again. Gasoline has about 700,000 BTU/gallon or 205 kWh/gal. a gallon weighs 8.3 lbs or 3.8 kg. So that's 53 kWh/kg. (wait, I screwed up something somewhere before, because I just ran through it again and that number seems different than I recall. But the point remains the same.)
So to get a 400 mile range out of an average ICE-powered car, you'd need about 100 lbs or less of fuel. That contains as much energy as you'd get from approximately 4,500 lbs. of your batteries.
Or to put it another way, that's what would be needed for the idea of storing electricity on board to be as practical for the end user as simply running an ICE. Of course, in the real world, assuming that this magical energy density comes with the ability to charge and discharge quickly, you'd actually see some additional benefit from regenerative braking, but that would depend very heavily on maximum charge rate.
Or to put it a *third* way, since the Prius seems to be getting about the same gas mileage as some comparable Diesel cars, there's really ZERO advantage to all this extra complexity and monkey motion until we can make a significant decrease in the weight of our batteries, and/or dramatically increase their ability to take a fast charge to take advantage of regenerative braking, or both. Because I dunno about you, but when presented with two machines that are equally efficient, but one is half as complex as the other, I'll take the simple one every time. It's going to take a dramatic increase in gas mileage above and beyond what I can get out of a well-tuned ICE to make me take the plunge.

No, no it won't. Not unless you enjoy driving something like an overgrown golf cart.
nate
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Nate Nagel wrote:

But everyday commuting *isn't* 500 miles.
All a hybrid needs is enough battery capacity to run its daily comuting run on the battery. Any more is wated capacity quite frankly. The idea obviously being to recharge off mains electricity at work, home or elsewhere.
The ICE only needs to kick in when a longer range is required and it'll happily cover as many miles as you care to provide fuel for.
Graham
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Eeyore wrote:

Not in England, maybe.

You can really only rely on "home."

Sure, but that implies a) a breakthrough in battery technology that hasn't happened yet (a serial hybrid isn't practical ATM because of battery limitations) and b) a LOT more stored energy than you're allowing for.
nate
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Nate Nagel wrote:

Not anywhere.
Graham
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wrote:

I personally have probably logged 500 miles in a single day's work before. Over the course of two days, quite often. Before I moved, it was 50 miles from my house to my office. throw a couple job site visits in and you're there.
I know that there are people that live in PA that commute back and forth to Baltimore every day. People live where they can afford, and work where they can get paid.
nate
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N8N wrote:

It wasn't commuting though was it ?

Well, a hybrid can do 500 miles day too. It just needs to burn some fuel to do so and when it does burn that fuel it uses it more efficiently than an ICE can.
Graham
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Nate Nagel wrote:

Things are changing already. Today. NOW !
http://www.motorauthority.com/news/hybridelectric/london-gets-free-electric-car-recharge-points /
http://www.greencarcongress.com/2006/12/london_provides.html http://www.westminster.gov.uk/environment/pollution/airpollution/Ecomark/incentives.cfm
" Electric vehicles:.................. Free recharging points are also available in 13 of our 17 car parks. "
FREE electricity too ! They really want to reduce pollution.
Graham
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Nate Nagel wrote:

It implies no such things at all.
I suggest you calculate how much energy it takes to move a fairly normal size car at say 80 mph. You might get a shock how little it is compared to the output of ICEs.
The equations for rolling resistance and air drag are readily available if you search.
That's why you can 'get way with' as little as 15kWh of stored energy.
The onboard ICE will also come in handy for winter heating too. It's nuts to use energy in the battery for space heating.
Graham
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wrote:

You're neglecting that you need a power reserve in an electric car too. that means not only bigger, heavier motors than required for steady state cruising, but extra battery capacity as well. I don't know about the cutting edge technology batteries, but the sealed lead- acid deals that I am familiar with don't like to be discharged at a rate greater than their amp-hour rating, as a rule of thumb. (i.e. if you have a 50Ah battery, you don't want to discharge it at a rate much above 50A to prevent damage.) I would assume that similar limitations are found with other batteries, although I don't know if they correlate the same way or not.
nate
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N8N wrote:

I'm not neglecting it at all.

You need those just to provide acceptable acceleration.
The power required for cruising at 70 mph is a mere 30 bhp (22kW).
22kW of motors will give you asthmatic acceleration and the car will slow down on gradients so you'd probably fit ~ 45kW of motors just to cope with those two things. It would give you 0-60 in 9 seconds btw in a lightweight 1 tonne (2200 lb) body.
Fitting 45kW of motors won't increase the cruising power consumption or the average power consumption though.

Lead-acid technology is over a century old and is not relevant to a discusion about EVs.
The issue of charge and discharge rates is well understood. It's *NOT* rocket science !
Modern NiMH and Li-ion battries for high current applications address these issues.
Graham
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NiMH don't like to be discharged much above 1C either. LiPo can handle 6C, but no one uses them in cars.
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Somewhere in the vicinity of 65 horsepower. That's about what the original 3-cylinder Hyundai Excel had, and that's about as fast as the Hyundai would go.
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"Matthew T. Russotto" wrote:

Wrong by nearly 3:1.
Graham
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Nate Nagel wrote:

My calculations show 400 miles would need 125 kWh.A 125kWh battery *would* weigh 850 kg. But you never need 125kWh of battery storage.
You simply don't do those 400 mi on energy that was stored 'back at the ranch'. Depending on the scenario you top-up daily with mains electricity or generate your own as you drive when the battery starts to run 'dry'.
Graham
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Nate Nagel wrote:

Because it's over complicated.
Graham
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wrote:

And yet, it's the best hybrid available from a major manufacturer today.
You can point to vaporware all you want, but the truth is, the Prius is the most advanced hybrid vehicle that a major manufacturer apparently feels comfortable putting on the market, for whatever reason.
nate
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N8N wrote:

Putting on the *US* market.
Graham
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