The Electric Car
in [Design]
|
From: Eeyore on 29 Jul 2007 22:26 Nobody wrote: > Eeyore wrote: > > > Consider the impact on the environment of > > scrapping/recycling all those batteries every few years as well. > > Which? Scrapping or recycling? > > Any battery large enough to power a car for 250 miles is bound to get > recycled. > > The only reason anyone would consider the possibility of large batteries > being routinely scrapped is if they are intentionally trying to make the > figures look bad. So what is the impact of recycling huge batteries every say 3-5 years ? Graham
From: Phil Allison on 29 Jul 2007 22:42 "Nobody" > >> Well from what I have read they already are pretty good - 250 miles on >> one charge. That's not bad. Better acceleration than a Porsche. > > But at what speed? ** Over the range from 0 - 60 mph - according to the makers. Achievable in a bit over 4 seconds. > Energy = Force * Distance, so the more force, the more > energy required. ** The force is less than 1G for any normal car - since tyre to road friction is less than the weight of the car. 0 - 60 mph in 4.3 seconds requires a continuous force of just on 0.64G - plus the effect of increasing air drag at higher speeds. > At anything much above jogging speed, air resistance dominates, ** Air resistance dominates the terminal speed ( said to be 130 mph for the Roadster) - but tyre grip and engine power limits acceleration in the range from 0 - 60 for a very low drag car like the Roadster. ...... Phil
From: Nobody on 30 Jul 2007 06:22 On Mon, 30 Jul 2007 12:42:26 +1000, Phil Allison wrote: > "Nobody" >> >>> Well from what I have read they already are pretty good - 250 miles on >>> one charge. That's not bad. Better acceleration than a Porsche. >> >> But at what speed? > > > ** Over the range from 0 - 60 mph - according to the makers. > > Achievable in a bit over 4 seconds. Ah; I should have removed the "Better acceleration than a Porsche" bit. What I meant was: >> Well from what I have read they already are pretty good - 250 miles on >> one charge. That's not bad. > > But at what speed? IOW, at what speed can you get 250 miles on one charge? Energy per unit distance increases with drag and thus with speed. >> Energy = Force * Distance, so the more force, the more >> energy required. > > > ** The force is less than 1G for any normal car - since tyre to road > friction is less than the weight of the car. > > 0 - 60 mph in 4.3 seconds requires a continuous force of just on 0.64G - > plus the effect of increasing air drag at higher speeds. Here, I'm talking primarily about force due to drag, which is proportional to the square of the speed. E.g. drag at 70mph is roughly 36% higher than at 60mph, and almost twice that at 50mph. Energy per unit distance increases likewise. >> At anything much above jogging speed, air resistance dominates, By which, I meant that it dominates over constant frictional forces (rolling resistance). Under heavy acceleration at low speed (i.e. 0-60 or standing 1/4 mile), the force required to accelerate will be the main factor, but that's recoverable with regenerative braking, while energy used to overcome drag and friction is lost for good. > ** Air resistance dominates the terminal speed ( said to be 130 mph for > the Roadster) Wow. The force required to overcome drag at 130mph is ~4.7 times that at 60mph. IOW, if the "250 miles on one charge" figure was for 60mph, you wouldn't get much over 50 miles at 130mph.
From: Nobody on 30 Jul 2007 07:03 On Mon, 30 Jul 2007 03:05:17 +0100, Eeyore wrote: >> IOW, for urban driving, electricity has everything in its favour. For long >> distances on fast roads, the only way an electric vehicle is going to be >> viable at present is to include a combustion-driven generator. > > That's a hybrid. The *series* hybrid doesn't attempt to do any fancy mechanical > combining of traction power from an ICE with the electric motor and simply uses > the ICE to recharge the battery, thus making it much simpler than a parallel > hybrid. Do such things exist in production? The main disadvantage with that is that all of the power has to come through the motors, even at maximum speed. With a parallel setup, you get the sum of the two rather than just the maximum. The advantage is that you don't have the layout constraints (transmission tunnel etc) or complexity of a mechanical drivetrain. >> Using a generator to drive an "electric" vehicle isn't necessarily as >> crazy is it may sound. An electric drivetrain with a generator running at >> constant speed/load could conceivably be more efficient than a mechanical >> drivetrain and the need for the engine to have a wide operating range. > > In a series hybrid, the ICE can always run at optimum efficiency (rpm), which it > doesn't in today's ordinary cars. Not having to be able to vary the speed means that you could use a turbine engine; unfortunately, the high cost of those seems to be largely inherent (i.e. they still wouldn't be cheap if Ford/GM were making a million units a year). > Also, overall system efficiency is improved by > the use of regenerative braking. Plus, of course, with a series hybrid, you > don't need to use the ICE at all for short journeys. It seems to have all the > right cards in its hand. > > OTOH, are they even necessasry ? What? An ICE generator? Until there's either a quantum leap in battery technology or we get some alternative means of turning fuel into energy, e.g. fuel cells, they're about the only way that you're likely to get decent range (the cited 250 miles would need to get you "there" and back again unless you have some way to recharge while you're there). First, there's the energy density: 1 litre of petrol/diesel has a lot more energy than you can store in 1000 cm^3 of battery. Second, there's the infrastructure. A fuel tank only needs enough capacity to get you from one petrol station to the next. Until there's similar infrastructure for electric vehicles, being able to "recharge" by refuelling a generator is likely to make a significant difference to viability for long distance journeys. OTOH, I suspect that there are a lot of people for whom it would suffice to own an all-electric car (even with fairly limited range) and hire a "real" car as and when they need it. Unfortunately, rationality and cars don't necessarily go together; a lot of people would automatically rule out a car with a 100-mile range even if it was only inadequate once or twice a year.
From: Nobody on 30 Jul 2007 07:36
On Mon, 30 Jul 2007 03:26:29 +0100, Eeyore wrote: >> > Consider the impact on the environment of >> > scrapping/recycling all those batteries every few years as well. >> >> Which? Scrapping or recycling? >> >> Any battery large enough to power a car for 250 miles is bound to get >> recycled. >> >> The only reason anyone would consider the possibility of large batteries >> being routinely scrapped is if they are intentionally trying to make the >> figures look bad. > > So what is the impact of recycling huge batteries every say 3-5 years ? Probably not a great deal. The energy consumption is likely to be miniscule compared to what a vehicle uses in 3-5 years. As for pollution: the usual metals (lead, nickel, cadmium, lithium) are valuable enough that you are going to try to recover as much as possible simply on economic grounds (and these aren't particularly hard to recover). I don't know what else might be an issue, but it's usually the heavy metals which are cited in anti-EV FUD. Organic pollutants are a total non-issue if you're comparing against ICEs running on hydrocarbons. |