I would think the efficiency of a two cycle is low. 37 kw is also way large. 10-12 kw would be ideal. And there is still the problem of getting a decent generator. The only good ones I know of, are the Honda Invertor types, but only up to 6.5 kw.

How come your previous 1 kwh?

Also you wrote previously...
"The peak load that the motor draws is a design concern, with reduced battery size, more load per cell, but this is easy to accomadate by storing peak load in a capacitor bank on the PEM DC bus - that peak load is only used on extreme accelerations (i.e. 0-60 in 3.9 secs), so the total energy the capacitor bank must store is quite small."

Are you believing the 0.2 kwh is enough for the 0-60 in 3.9 secs?

Ken@Japan

tzero uses max 20 kw generator by Kawasaki 500cc engine.
http://www.acpropulsion.com/Products...g_trailers.htm

Ken@Japan

185 kw peak x 3.9 secs / 3600 secs/hr = .2 kwh

This would be about maximum kinetic energy storage, perhaps a little more if you went to 80 mph say

The 1 kwh would also encompass the potential energy storage of a large hill + the kinetic energy storage at the top of the hill

That would be a good size for a general purpose generator for EV's - which have a large variety of sizes, weights, efficiencies and desired applications, and of course you need extra average power to pull a heavy trailer at 80 mph.

I see your system is 100% efficiency.

Ken@Japan

This is a good point, one that I have been saying for a while. I think that using a bank of ultracapacitors, along with a more powerful motor, would be a great idea for all hybrid vehicles. As it is, regenerative braking is substantially limited, on most current cars to about 1/2 half of the peak battery output -- on my Civc, the motor has a max output of 100amps, but can only regenerate 50amps.

In general a shift toward more powerful motors, along with enough ultracapacitors would allow much more effective regeneratve braking, and could minimize friction brake use to outright panic stops, and holding the car still on hills. The battery should also last significantly longer, and would't heat up as much (which increases resistance and decreases efficiency).

That 37kw is a peak power, I'd guess the engine is most efficient at about a third to half of its output. Having an engine with some power in reserve may be a good thing however. Most of the time, the engine could run at its most efficent RPM and load, but in the case of severe driving, such as driving up a long mountain incline, the engine could ramp up output. Another useful scenario would beif the batteries are too cold to provide full current, it could both supply extra power, and heat them up.

As far as the engine only having two cylinders, that would be less of a problem on a series-hybrid design-- since the motor isn't directly driving the wheels, the more unevent power production (only one power stroke per crankshaft rotation) wouldn't be as much of a problem. A bigger flywheel could be used if desired as throttling is not an issue, it would also never be idling at low rpm (very choppy)

If EESTOR actually come up with the goods, then this would be true, but they are being very secretive and no samples have been given for testing. They are meant to have up to 280 Wh/kg.

Another false dawn in ultracapacitors was JEOL, who claimed to have a 75 Wh/kg ultracapacitor which was meant to be on the market by 2004. Again, nobody has been given a sample to test their claims.

Today the best ultracaps you can actually buy are about 10 Wh/kg (as used in the Nissan diesel hybrid truck), which would mean a 1 kWh capacitor bank would weigh about 220 lbs.

http://mysite.wanadoo-members.co.uk/ecotech/ecot.htm

evone- You mentioned 1KWH of ultracaps weighing .8LBS. These are capacitors no one can buy and no one outside of EESTOR can verify exist. Go to www.maxwell.com and look up their BPAK0020. These are the ultracaps that actually exist today and their energy density is 2.72 watt hours per Kg. You would need about 800LBS of ultracaps to get 1KWH.

Another important point to consider is: What is the comparison between frontal area of these 2 vehicles (tesla and prius). There is more to this than just C of D.

You are quite right, the 8 lb EESTOR Ultracaps remain only a promise at the moment. MIT is getting quite a lot of publicity about its nanotube caps. See: MIT Caps

The ProPulse Series Hybrid electric drive for Army Transport Vehicles uses Ultracaps, rather than batteries, and they must be > 10 kwh I would estimate.
See Oshkosh Truck Co .

The difference in drag coefficient between the Tesla & Prius would not be a significant factor in calculating combined fuel economy. Even at 60 mph, on 0% grade, the difference between an aerodynamic small car & a non-aerodynamic small car is about 10% in power req'd, and both the Tesla & Prius are both aerodynamic small cars. At most would account for 5 mpg difference. Could be calculated more accurately if you knew the drag coefficent for each vehicle.

The assumption is that eventually ultracaps will be suitable for series hybrid vehicles, and there is every reason to believe they will be within the next ten years, esp if the Series Hybrid vehicle becomes common. However, it is not really important for this calculation, there are Lithium Ion batteries that can have a 95% charging efficiency, which would more than suffice, and the charging energy loss for a series hybrid is mitigated by the fact that the generator is directly supplying the PEM DC bus, rather than charging the batteries for much of the time, so if charging energy loss is 15%, a reasonable estimate is that in the series hybrid the energy loss would be more like 7%.