They got - at an average speed of 50mph - a figure of 217Wh per mile
Now I accept that they were probably driving in the sort of way that those idiots trying to 60mpg out of skoda diesels drive..but its still a data point.
That means to achieve 500 miles range they would need just 10KWh.
This on a 200bhp sports car..
I still reckon that to get serious range at sensible power levels you need around 50KWh.
Even taking my tiddly little lithium batteries at 150Wh/kg, thats only 333kg. and about 167 liters of space. (I just measured mine. 36Wh in 120 cc of volume)
Thats a cinch to fit in a car. Under the floor. I mean a petrol tank is 60 liters in a decent one..this is not even three times that.
Add in lets say a kilowatt per kg of the rest of the power train (easily achievable) the motor(s) and control gear would weigh in around 150kg
so about 483kg for the 200bhp power train.
Thats the practicaliies
Now for fuel efficiency and economy.
Comparison with diesel at 10kw/litre (http://xtronics.com/reference/energy_density.htm ) shows that to be *as efficient* that diesel ought to be able to do a 100 miles on just two liters of fuel. In fact its more like two GALLONS showing that the diesel is, with respect to the electric car (neglecting charging and generation inefficiencies) about 27% efficient. That bears out my gut feeling that a diesel is at its very very best, capable of about 40% thermal efficiency, and is probably operating at less than 30% even in the most favourable regimes. And far far worse idling at traffic lights :-)
taking not the 200Wh/mile figure, but somethig nearer 400Wh per mile, as being realistic and figuring on an overall 80% charge efficiency, you get 2 miles per unit of electrical input. So whats that - 5p a mile worst case. At sort of off peak prices you might be down to 1.5p a mile or better.
With diesel at £3.42 a gallon and doing 50mpg, thats 6.8p a mile.
Overall energy efficiency.
If we take an average of 50% power station efficiency, 90% transmission efficiency and 80% charge efficiency (these are realistic figures, according to experience and what data I could find) and apply that to the figure of 217wh per mile, we get 36% overall losses...so 602Wh per mile is what the power station has to BURN to get the car doing its stuff.That, applied to diesel at 10KWh per liter gives us an overall 'fuel consumption' of 62mpg...on an economy run. So overallI reckon there is nothing to choose.
to charge 50kWh overnight in ten hours is a peak rate of 5Kw. Somewhat beyond a 13A socket, ...but NOT beyond a 13A ring, which is typically rated at 30A or 7.5kw. Its certainly less than the load a cooker spur - rated on a 40A 45A or 60A trip - could handle.
A fast charge at a service station WOULD be a challenge. If the batteries would take a half hour charge - after 500 miles you'd need that sort of break anyway - you are looking at 100KW - say 300A at mains voltages.
Chances are however in the UK that 500 miles is all you would ever need to do in a day. Keeping your 'tank full' would be basically what you would do every night.
Sadly this makes 'on street' parking a thing of the past :-) No bad thing anyway IMHO.
On street users would have to drive to Tescos and charge their once a week while they did their shopping :-)
Or get the AA out with their 400KW batteries and get a 'tankful'..or at least enough to get them to where they could charge.
Cost of cells and operations Mmm. This is the current killer. I paid about $6 per watt hour for a bargain buy. that puts the cost of the 50kWh pack at $300,000 in terms of what is currently actually in production. Say £200k. ;-)
Motors? well a halfway decent vacuim cleaner motor is about 50 quid for a couple of bhp so 5 grand should net you 200bhp of electric motors. Not an issue there.
We reckon to get 200-300 cycles out of a pack...at 500 miles range, that comes out to 100,000-150,000 miles. Acceptable. Amortise the pack cost even at 200,000 pounds, and you are up to a shade over 2pounds a mile. That is not cost effective, but its not so far outside what would be cost effective on a big luxury car (and I think that is where this sort of thing may actually come in first - not in town cars, but in big Lexus style cars, where the utter smoothness of the electric drives will be seen as a great benefit) When you consider that there should actually be - apart from possibly brake pad and tyre changes NO SERVICE COSTS AT ALL (ok, maybe a squirt of oil and grease somewhere..) it actually gets to look a bit more sensible.
Apart from inertia, and battery costs,nothing is stopping anyone from building a top class electric car.. the technology exists to build an electric car that would certainly perform as well as, and in many ways better than, a current state of the art diesel, with no worse overall fuel economy from oil well to street mile, and conceivably better.
It could be charged overnight, have a top speed in excess of 120mph, a performance rivalling any car in the 200bhp class, and have a 500 mile range driven reaosnably gently (and with the whole motor system under computer control, thats nothing more than setting a switch..)
Its oin-street pollution would be zero, and due to the fact that the power stations can certainly act more realistically to sink carbon and have higher thermal efficiencies than a car can, its overall pollution would be less.
If nuclear power to generate electricity comes along - or other green energy generation methods - it has to be seen in a new light: How does it compare with
- biofuels - nuclear electric to hydrogen in IC engines - nuclear electric to hydrogen in fuel cell electrics
It matches biofuels directly in the same way as burning diesels does now. I.e. not a lot in it. Once you burn biodiesel you end up with the overall 20-40% efficiency. The more efficient power station is offset by the losses in transmission and charging.
It knocks the spots of hydrogen, because fuel cell efficiences are simply limited by the same sorts of efficiency limits that limit heat engines. With hydrogen you get a double whammy - creating it is inefficient and so is burning it. If we didn't have suitable batteries, it woild be the only answer ...but we do..
Batteries are simply the best way to store electrical energy bar none in terms of efficiency. And lithium batteries are small enough and light enough for all but extremely high power or long duration use. I.e. not for boats, and not for aircraft Well not airliners. I reckon that if it hasn't happened already, the first man carry ing microlight or glider powered by lithium batteries is months away only.
Why aren't peole doing it?
I think two reasons
Firstly, the 'green' tag is flawed unless the electricity comes from other than fossil sources. As I feel I have demostrated that the overall fuel efficiency is similar to class diesel car. (performance is BETTER though ;-))
Cost. The batteries are simply way too expensive right now. Ther is however absolutely no reason why they should be...there is nothing intrinsically expensive about a lithium polymer battery. In massive volumes, one might expect them to be cheaper than lead acid batteries ultimately.
This is why I think Tzero have the better approach, and the Priuset al are deeply flawed from a marketing perspective. Electric cars have not actually - until mated with a nuclear generating backbone - got any green points to make. What they do offer, is extaordinary peak power to weight ratios, but good econonmy at cruise, coupled with almost vibration and noise free operation. That puts them straight into the luxury market.
ULTIMATELY when the batteries are cheap you wiill see them being turned out as mass market shopping trolleys, but not yet. The high level of development money needs to be recouped in more profitable markets.