shallowdeep
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Joined: 9/1/2006
From: California
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quote:
ORIGINAL: LadyEllen
It occurred to me that when I go out to start my petrol car in this weather, it can generate enough power to defrost my windscreen and rear screen and drive fans and warm the interior, and light the headlamps, power a radio and keep my cellphone charged, and still go 0-60 in about 8 seconds (ice permitting) and travel approx 500 miles on one tank of fuel doing all of this.
Can an electric car do the same?
Well, there are really two separate questions you are asking. The first deals with power: Can an electric car's batteries power a heater, a motor, headlights, etc. simultaneously? Yes, this is not an issue.
The next question deals with energy: Can said car travel 500 miles on a single charge? The current answer is no, but that has little to do with the weather.
As has been pointed out, chemical fuels have a far greater energy density than batteries. As a result, battery powered cars have a more limited range despite their increased efficiency. But passenger heating, even in very cold climates, really doesn't add that much to the energy requirements. A mid-size car in the US is defined as having a maximum interior volume of 3397 L. Using a volumetric specific heat capacity for air of 20.8 J/mol-K, and assuming a relatively large interior/exterior temperature differential of 50ºC (90ºF), you'd need about 158 kJ to heat the interior. That amounts to only 0.08% of the capacity of a presently realizable 53 kWh, 450 kg battery pack like that found in the Tesla. I don't have numbers for the heat flux typical from a car, but – even assuming you had to fully reheat that entire volume every minute – you'd still only use 24% battery capacity over a five-hour trip. Utilizing a heat pump rather than a resistive heating element could cut that by a factor of 2 or more.
quote:
ORIGINAL: ThatDamnedPanda
The point I'm making is that using electricity to heat the interior of a vehicle when it's below zero fahrenheit requires such an enormous battery capacity, you can not possibly carry - in a mid-sized passenger car - a battery large enough to both propel the vehicle for 250 miles, and heat it for 5 hours. You just can't come close to it with current technology. Using electricity to create heat is just too inefficient.
Chemical fuels obviously do pack more energy, but – even when harnessing a small fraction of the heat for warmth – the vast majority of that energy is still dumped as waste heat. Even at -30ºF, the difficulty lies less in keeping things from freezing than in preventing them from cooking. The amount of energy required to keep things warm isn't nearly as large as you are assuming. Therefore, while an electric vehicle would see some losses in cold weather that a combustion driven vehicle would not, the effect is more like running air conditioning in hot weather; it's not an insurmountable energy drain... unless I messed up my calculations, of course. :)
From the user perspective, an all electrical system actually has a nice advantage - you can heat things up quickly, and with no need to wait for the car to warm up first. The Tesla's batteries could, for example, deliver enough power to heat a car from -30ºF to +70ºF in less than a second after pressing the ignition. In practice you'd probably slow that process down a bit to avoid melting the heating elements, but you'd still get lots of hot air coming out of the vents instantly, something I imagine would be welcomed by most people on a frigid morning.
Still, independent of climate control, the range of battery powered cars remains an issue. A couple hundred miles is presently expensive, but doable; much more and the batteries start to weigh (and cost) too much. Perhaps worse, there is no way to quickly "refuel" – few people have the patience to wait a few hours to recharge in the middle of a trip. Especially if it's cold. For commutes electric cars are nice, but they lack the flexibility to take longer trips – a limitation which greatly hinders the appeal. Hybrids are more popular for a reason.
Extremely low operating temperatures can be an issue for batteries, since the chemical reactions are slowed. You would probably need to add heating elements around the battery pack to charge at -30ºF (not a big deal since it's already plugged-in) and might also have to divert some energy to those elements while in operation.
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RE: electric cars & the deepfreeze - 
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