fooljoe said:
edatoakrun said:
As per my OP, I think the optimum ratio of battery kWh available to kW generated while you drive will probably be somewhere between 4/1 and 2/1, for most BEVx vehicles.
Sorry I didn't want to search this 27 page thread to see your OP...
I'd think the optimum kW is simply that which provides enough power to break even while cruising at 70 mph on a level road (somewhere in the 20-40 kW range, perhaps), regardless of battery size.
I disagree, and believe that a ~20 to 30 kWh available battery pack
with driver-selectable ~5-15 kW
range extender is probably optimum for most passenger vehicles, as this is all that is required for almost all desired trip lengths, in almost all driving conditions.
IMO, a BEV should never need to depend on a an ICEV (or other type of range extending generator) for all the kW required by the vehicle.
The RE kW allows charging-while-driving, to allow the driver to extend the BEV range between stationary DC charge stations, where long distances between or other particular range challenges (such as large ascents and/or low temperatures) would otherwise require charge stops more frequently than desired.
See the example of the ~70 kWh trip, with one recharge stop, requiring only a ~20 kWh battery pack and ~8 kW range extender, which I posted ~3.5 years ago, at the start of this thread, copied below, since you didn't read before replying:
...a true ICE ”range extender” for a BEV is not a bad Idea, It's just that current designs are all abysmal failures, from the point of energy efficiency and driver utility. Putting an ICE drivetrain in an EV, whether in series, parallel, or any other hybrid configuration, is not advisable, IMO. Invariably, you will get an overweight, overpriced, underperforming vehicle, like the Volt. It seems almost as ridiculous, to install an extremely expensive and heavy large battery pack (like the Tesla S long-range options) which is only occasionally required by the BEV driver.
A functional range extender would consist of:
A small displacement (200-600 CC) ICE generator, run at highest-efficiency rpm, to recharge the battery pack. Generator output would not be sufficient to drive the vehicle, just enough to extend the battery pack range to the next convenient recharge location.
It would not run on gasoline, but a less polluting, and more stable fuel, such as propane (easier refueling) or CNG (lower cost). 5 gallons of Propane, for example, would probably offer about 200 miles of range extention for a LEAF-sized BEV.
The fuel would also be available to a combustion cabin heater, the one use for which battery energy storage is particularly inefficient.
I think this could be integrated into the design of BEVs (and maybe even as a portable unit, and available for rent, as many have fantasized) at lower cost, and lower weight, than the huge battery packs some BEV manufactures seem to think are advisable.
So, say you are a San Francisco Bay Area resident. You usually keep the heater set to propane by default in the winter, extending the range by about 10% and reducing battery cycling accordingly, without even using the ICE feature. You refill the 5 gallon propane tank once a month or so, just to supply the heater.
When you want to take the BEV on the occasional longer drive, say to Tahoe for a weekend of skiing, instead of making 3 or 4 stops (with a 20-30 available kWh battery pack) for DC charges, you just turn on the ICE generator during your trip, as soon as your battery capacity drops to a level to efficiently accept charge, while you and your passengers are kept toasty warm by the propane heater. You stop for one 30 minute 80% DC charge at Auburn (120 miles in 2 hours of driving, about 20 kWh consumed from the battery pack, and 16 kWh used from the generator) and top-off the propane tank (you only used a few gallons) at the adjacent minimart. This is just enough generator-assisted charge to get you the last 80 miles over Donner Summit to your destination, but you never get “range anxiety" (or BEV "freeze anxiety" about road closures or delays, due to weather) as you know that if you get the “very low battery” warning, you can just pull off the road, and if there is no charge station (or only a L2) nearby, you can always find a place to stop for a short break, while you self-recharge for the last few miles, using your generator. And if you get stuck behind a semi that jackknifed in a snowstorm, closing the road, you can watch the generator add bars to your battery, as the propane heater keeps you and your passenger comfortable, while you wait for the road to be cleared.
I believe BMW may be the only manufacture currently contemplating this true ICE “range extender” option, for its BEVs...
As it turned out I was disappointed by the i3, for the following reasons:
1) Wrong hydrocarbon fuel:
Why would you want to use gasoline for an ICEV you might only use a few times a year, when their are less polluting and far more stable alternatives?
I will add, that the future of the natural gas infrastructure looks far more doubtful than it did years ago (before the recent gasoline price collapse) so propane, which already has a well-developed infrastructure in the USA, seems the clear fuel of choice today.
2) Wrong in limiting the use of hydrocarbon fuel:
Once you have a hydrocarbon fuel in your tank, it's foolish not to add the far more efficient option of direct combustion for cabin heating.
3) Wrong size ICEV:
Oversizing the ICEV severely degrades the i3 BEV efficiency, adding much more weight and cost than necessary.
4) Wrong utilization of the hydrocarbon fuel/ICEV:
If you tried to take the trip I posted above in an i3, you almost certainly could not make it in comfort and safety, not in USA (maybe not even in even euro) spec for remaining battery capacity when starting the ICEV
is allowed, and much of the energy from the hydrocarbon fuel you used would have been wasted by burning it in your (<25% efficient) ICEV, rather than by using it in a (>75% efficient) cabin heater.
Somewhere short of Donner Summit you would probably find yourself with a depleted battery, trying to climb a steep grade and keep up with a lane of traffic moving at ~60 mph with a heavy load in below-freezing temperatures.
Requiring ~50 kW, and having only ~25 kW available from your i3's ICE, would not be much fun.
I can't emphasize how stupid it is, IMO, to install any range extender in a BEV, then
put its operation outside of the control of the driver.