The “range–extended” EV (BEVx) considered

[AndyH]

Another variation on charge while you drive described below.

I'm extremely skeptical as to whether fuel cells will ever be viable for vehicle propulsion, for the simple reason that they are far more efficient when installed at BEV charge sites, where they can be fueled from the existing natural gas infrastructure and where the waste heat generated is easily recoverable.

"Viable" is a strong word, especially since this tech has already been proven for vehicle propulsion. There is zero need for a fuel cell to be connected to the natural gas infrastructure (I'm assuming you're looking at lower pressure and not suggesting that fuel cell = fossil gas?). There are alkaline electrolyzers in use today that connect to electricity and water and output very high pressure hydrogen without pumps. One device and no moving parts is pretty efficient...

The 'waste' heat is very useful for vehicles in the majority of the world - in large parts of the US that heat is very useful for up to nine months per year. Considering that we've had things like propane-powered refrigerators for many years, I'll bet there's a way to use the waste heat across the southern US in the summer as well.

 

[edatoakrun]

...I'll bet there's a way to use the waste heat across the southern US in the summer as well.

There is a practical way to use fuel cell waste heat at charge sites year-round, but not in vehicles.

At every site suitable for a BEV DC charge station (restaurants, hotels, etc.) there is a requirement for water heating.

Of course, during the peak in solar generation during the summer in mid-day, the operator probably would prefer to shut down the fuel cell, and utilize the grid-surplus solar, and use solar thermal directly for water heating.

But we are going off-topic.

 

[fooljoe]

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, but why would you think that there's an optimum, constant ratio of kWh to kW? If anything, I'd think the two would be inversely proportional - i.e. the more battery you have the less range extending power you'd need and/or could afford or fit. But really 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.

 

[AndyH]

...I'll bet there's a way to use the waste heat across the southern US in the summer as well.

There is a practical way to use fuel cell waste heat at charge sites year-round, but not in vehicles.

At every site suitable for a BEV DC charge station (restaurants, hotels, etc.) there is a requirement for water heating.

Of course, during the peak in solar generation during the summer in mid-day, the operator probably would prefer to shut down the fuel cell, and utilize the grid-surplus solar, and use solar thermal directly for water heating.

But we are going off-topic.

Not off topic at all, as cabin climate is a critical aspect of BEV range. The simple fact remains that there is precious little 'waste' heat from a battery pack, while using the available heat from an on-board fuel cell increases efficiency of the fuel cell stack from 45-55% to above 80%. And yes - that heat can be used to both heat and cool the cabin. Look at the simplicity of a propane refrigerator for one example (and hydrogen's already part of their process).

It works like this:

Heat is applied to the ammonia and water solution in the generator. (The heat comes from burning gas, propane or kerosene.)
As the mixture reaches the boiling point of ammonia, it flows into the separator.
Ammonia gas flows upward into the condenser, dissipates heat and converts back to a liquid.
The liquid ammonia makes its way to the evaporator where it mixes with hydrogen gas and evaporates, producing cold temperatures inside the refrigerator's cold box.
The ammonia and hydrogen gases flow to the absorber where the water collected in the separator in step No. 2 mixes with the ammonia and hydrogen gases.
The ammonia forms a solution with the water and releases the hydrogen gas, which flows back to the evaporator.
The ammonia-and-water solution flows toward the generator to repeat the cycle.

http://home.howstuffworks.com/refrigerator5.htm

There are much more appropriate, efficient, and less expensive sources of electricity and heat for restaurants, hotels, etc. - and they include PV, solar thermal, on-site biogas feeding water heaters, or multi-building district heating from a combination of solar thermal, biogas, and possibly excess PV once the batteries are full.

Fuel cells are a perfect high-efficiency range extender for BEVs and it's good to know that they're on the road in exactly that capacity in vehicles from small vans through class-8 trucks as we 'speak'.

 

[edatoakrun]

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.

 

[AndyH]

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.

Build and sell one and see what the general public does with your baby - and how it affects your liability insurance rates and legal expenses. :lol:

 

[edatoakrun]

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.

Build and sell one and see what the general public does with your baby - and how it affects your liability insurance rates and legal expenses. :lol:

Sorry, but I have no idea what your point is.

I have often wondered about the legal position of any PHEV/BEVx manufacturer following an accident alleged to be caused by the vehicle design.

Any vehicle which is designed to allow the driver to continue driving following battery depletion, whether this is only a slight reduction from full power as in the Chevy Volt, or a drastic drop in power as in the i3, could cause (or at least be blamed) for many types of accidents.

I would certainly not want to be passing a truck on a two lane highway in an i3, when the battery power cuts out, leaving me with only ~25 kW from the ICE.

 

[AndyH]

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.

Build and sell one and see what the general public does with your baby - and how it affects your liability insurance rates and legal expenses. :lol:

Sorry, but I have no idea what your point is.

It's not at all veiled. Many of the people here are engineers, others are tech or DIY types that will take the time to understand how to operate devices with which they play. The general public? Not so much. Add the litigious nature of the 'developed' world, especially the USA, and it's pretty clear that automakers would much rather trust a microcontroller to make critical decisions rather than trusting their cash flow to operators that may or may not be impaired by chemicals or their iPhones or an impending business meeting. For a more in-depth exploration of this, note the explorations of self-driving cars.

 

[fooljoe]

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
...
Requiring ~50 kW, and having only ~25 kW available from your i3's ICE, would not be much fun.

Hmm, you begin your post by disagreeing with my assertion that 20-40 kW is optimum, suggesting 5-15 kW would suffice, yet then you end your post with a criticism of the i3 that suggests you think that its 25 kW extender is underpowered. This leaves me a little confused. :/

Anyway, it's silly trying to argue what the "optimum" would be, because we've not defined what metrics should be used to judge a hypothetical range extender. REs are, of course, different things to different people: Some just want something small that can bail them out if they come up a few miles short, others want something that can indefinitely sustain highway travel; some want something permanently installed on-board, others want something like a trailer that would only be used when needed and left behind otherwise; some want to leverage the most convenient fuel sources available (i.e. gasoline), others refuse to burn fossil fuels anywhere near their EV and would only consider an add-on battery or perhaps something exotic like a fuel cell. And of course there's everything in between each of these extremes.

IMO, if I'm going to go to the trouble of adding a range extender, I would see its purpose as serving to ameliorate the two drawbacks to long-distance travel in an EV: 1) Range is limited; and 2) Recharging opportunities are limited. On the first point, I'd rule out any concept that extends my range but keeps it limited, including add-on batteries and generators/engines incapable of powering the car on their own (at least on average - it's reasonable to assume some help from the battery for acceleration and hill climbing, e.g.) On the second point, I'd rule out any concept that uses a fuel source that's just as "exotic" as electricity, including hydrogen, natural gas, aluminum plates, etc. Gasoline would be the obvious choice, with diesel and propane as possibilities, since their availability is nearly as widespread. And as far as the other dimension, I'd strongly prefer to have a 100% EV with an add-on RE that would ideally be something I could rent only when needed, so I'm not stuck having to maintain an engine that I rarely use.

But again, all that's just my opinion. Ultimately I suppose only the market can decide what's "optimum" - if there ever is a market.

 

[BernieTx]

I think the Volt makes a great EV. My local deriving is all electric; and I can drive from Austin to the Texas coast without worrying about the non-existent DCQC and L2 charging network....

 

[edatoakrun]

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
...
Requiring ~50 kW, and having only ~25 kW available from your i3's ICE, would not be much fun.

Hmm, you begin your post by disagreeing with my assertion that 20-40 kW is optimum, suggesting 5-15 kW would suffice, yet then you end your post with a criticism of the i3 that suggests you think that its 25 kW extender is underpowered. This leaves me a little confused...

Maybe the thread below will explain the importance of giving the BEVx driver control of the generator:

I think I hate my i3 Rex...

...The key thing to learn - is you really need to get your REXs coded so you can enable the REX anytime you want. It makes it a totally different car and you can use it like an ICE. Run the battery down first to about 12.5%. Then use the REX till you get to a rapid. Add fuel, electrons and fill belly and thermal coffee cup and you are good for another 150 miles, and can either use another rapid - or splash the fuel from a jerry can...

http://www.mybmwi3.com/forum/viewtopic.php?f=2&t=2429&start=40" onclick="window.open(this.href);return false;

Though I don't suggest i3 drivers try this without considering the implications RE the manufacturer's warranty and your local air pollution regulations.

For example, it sounds like California i3 drivers who do anything to the specified generator cycle would not qualify for the $2,500 rebate, though I have no idea whether CARB thought out how it would enforce its counter-productive (IMO) BEVx provisions:

As a condition for receiving State of California, Air Resources Board (ARB) rebate funds...
Eligible applicants must meet requirements that include, but are not limited to, the following...

4.Not make or allow any modifications to the vehicle’s emissions control systems, hardware, software calibrations, or hybrid system.

https://energycenter.org/clean-vehicle-rebate-project/requirements/1003" onclick="window.open(this.href);return false;

 

[edatoakrun]

Wrightspeed unveils new turbine range extender for medium- and heavy-duty electric powertrains; 30% more efficient than current microturbine generators

4 May 2015

Wrightspeed Inc., a developer of range-extended electric vehicle powertrains for medium- and heavy-duty vehicles (earlier post), has unveiled the Fulcrum, a new proprietary turbine generator for use in its Route family of electric powertrains (Route for Class 3-6, Route HD for Class 7-8). The new 80 kW Fulcrum is a radial inflow, axial turbine, intercooled and recuperated. Fulcrum is a single shaft machine, the generator runs at turbine speed (~100,000 rpm). Weighing in at 250 lbs (113.4 kg), the Fulcrum is approximately 1/10th the weight of its piston generator counterparts and it is designed to have a 10,000-hour lifetime...

Sounds like a great application for city busses and delivery trucks.

Now if they would only deliver one ~1/10th that size, a ~8 kW microturbine, that weighs ~25 LB, and sells for ~$2,000, that I could install (along with the propane tank) in my LEAFs spare tire well...

http://www.greencarcongress.com/2015/05/wrightspeed.html" onclick="window.open(this.href);return false;

 

[edatoakrun]

A pro-PHEV paper below, includes criticisms of BEVx vehicles:

Using the PHEV (Plug-In Hybrid Electric Vehicle) to Transition Society Seamlessly and Profitably From Fossil Fuel to 100% Renewable Energy

17 July 2015

by Professor Andrew Alfonso Frank
CTO Efficient Drivetrains Inc. and UC-Davis Emeritus
and
Catherine J DeMauro

...5. The so-called Extended Range Electric Vehicle or EREV or BEVx. This concept is basically a PHEV with a smaller “range-extended liquid-fuel-powered electric generator.” The BMW-i3 and the Renault Kangoo are examples. These vehicles have a battery pack large enough for city driving but a very small gasoline engine and generator just large enough to recharge the batteries but not large enough to maintain full performance of the vehicle especially at highway speeds.

Unfortunately, this concept has some major drawbacks.

A. It is much less efficient than a properly-designed PHEV when using liquid fuel.


B. It will likely be abused by the user since he will now suffer from range and performance anxiety and would likely try to run the engine-generator constantly to keep his vehicle fully charged so his performance and range are not affected...

EREV (now being officially referred to as a BEVx) is actually a poorly designed PHEV; however, the car manufacturers will build whatever concept can be sold to their customers since they are profit and regulation motivated. Therefore, it is likely the lowest cost practical car that provides the benefits of moving toward zero net CO2 that will be a clear choice. The government’s job then is to properly incentivize the best ideas...

http://www.greencarcongress.com/2015/07/20150717-frank.html

As to A above, the author doesn't seem to understand that using while using an ICE as a generator is relatively inefficient, the occasional inefficiency which occurs only when a BEVx exceeds its battery range, is of far less consequence is than the constant vehicle inefficiency imposed on a PHEV by requiring it to be equipped with an ICE sized to provide vehicle propulsion.

As to B above, yes, as long as the DC charge network remains unreliable, the BEVx driver will tend to overuse the range extending ICE.

It is foolish however, not to understand that the DC network will only become dependable, when a fleet of vehicles that depend on them is on the roads, a development that sales of the DC-incapable PHEVs the authors advocate, are only delaying.

Ironically, it is the failure of government bodies "...to properly incentivize the best ideas..."
that has led to the dead-end developments of both PHEVs and the BMW I-3 "BEVx".

Both vehicles share the same fundamental design flaw, of using an ICE large enough to propel the vehicle, as a direct result of government incentives and mandates.

Both get the same federal incentive, $7,500, as do BEVs (and would any well-designed BEVx) equipped with batteries significantly larger than 16 kWh static capacity.

And CARB's mandate that the "BEVx" have an ICEV with a kW output sufficient for minimal propulsion, and its additional requirement that driver cannot initiate generator use until the battery is almost depleted, directly led to the I-3's poor design.

In fact both GM ( and all other PHEV manufactures) and BMW have chosen to use "lowest cost" ICE options, ICEs oversized for efficient integration in a BEV, simply because they could pull those ICEs off the shelf.

 

[gadyamit]

I like most of what you say ( edatoakrun)
But selecting small engine just because it is there is just part of the story...

I think that real good extended range engine should be small and very light. We use 100 + HP engines not to drive 70Miles per hour on the freeway, we use this extra power to accelerate fast... that’s all.

But in EV or PHEV we can use the battery for acceleration… So look at BMW i3 is doing exactly that small engine... It is NOT a complicated car like the Volt or the Prius it is simple car with extended range the right way.

 

[edatoakrun]

I like most of what you say ( edatoakrun)
But selecting small engine just because it is there is just part of the story...

I think that real good extended range engine should be small and very light. We use 100 + HP engines not to drive 70Miles per hour on the freeway, we use this extra power to accelerate fast... that’s all.

But in EV or PHEV we can use the battery for acceleration… So look at BMW i3 is doing exactly that small engine... It is NOT a complicated car like the Volt or the Prius it is simple car with extended range the right way.

I think we agree, at least mostly.

My main objections to the i3 are that the ICE is oversized, and uses gasoline, both of which excessively compromise its BEV performance.

I think ICE generators with five to fifteen kW output are optimal for most all BEVxs, and thatgasoline is NOT the best fuel for the x's ICE.

See my example of a LEAF sized vehicle, equipped with an ~eight kW generator, from my OP, from the first page of this thread:

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 extension 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...

IMO, the i3's generator is sized more appropriately for a truck or a very large passenger vehicle, one with ~the heft of a Tesla S or X.

A Tesla X (for example) equipped with a ~25 kW generator and only a ~50 kWh pack could easily make the same ~three hour ~200 mile Winter Tahoe trip non-stop, while a 90 kWh Tesla X BEV would probably have to stop to recharge en-route.

The hypothetical Tesla X50x25, would also cost a lot less than an X90, and due to the lower weight, handle better and have superior efficiency.

 

[gadyamit]

Yes, we are on the same page...
I remember reading about the I3, people where testing it climbing mountains with the ice engine running (empty battery). Only then the tester reported slightly reduction of power... so I agree with your point it means that ice engine is a little too big remember we carry it all the time and we do NOT need to test climbing.

BUT I think that the main problem in range extender solution is the Prius / Volt solution i.e enormous engine with small battery plus (complicated transmission a much more complicated solution). Toyota and Chevrolet engineers should go back to the drawing board and find a simple clever solution small engine just for charging… or maybe we still building a new conspiracy i.e. simple solution like BMW I3 is too simple, last longer and never break?

 

[ydnas7]

the problem with a range-extended BEVx is that a series hybrid is not as efficient as a parallel hybrid.
http://www.fueleconomy.gov/feg/Find.do?action=sbs&id=36030&id=35598
the BMW i3 is 3x more efficient in EV than ICE mode
vs
the Toyota Pip is 1.9x more efficient in EV than ICE mode
vs
the 2016 GM Volt is 2.5x more efficient in EV than ICE mode

the point is, gen to elec, elec to motor is less efficient than motor through gearbox to wheel

 

[epirali]

I like most of what you say ( edatoakrun)
But selecting small engine just because it is there is just part of the story...

I think that real good extended range engine should be small and very light. We use 100 + HP engines not to drive 70Miles per hour on the freeway, we use this extra power to accelerate fast... that’s all.

But in EV or PHEV we can use the battery for acceleration… So look at BMW i3 is doing exactly that small engine... It is NOT a complicated car like the Volt or the Prius it is simple car with extended range the right way.

I think we agree, at least mostly.

My main objections to the i3 are that the ICE is oversized, and uses gasoline, both of which excessively compromise its BEV performance.

I think ICE generators with five to fifteen kW output are optimal for most all BEVxs, and thatgasoline is NOT the best fuel for the x's ICE.

See my example of a LEAF sized vehicle, equipped with an ~eight kW generator, from my OP, from the first page of this thread:

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 extension 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...

IMO, the i3's generator is sized more appropriately for a truck or a very large passenger vehicle, one with ~the heft of a Tesla S or X.

A Tesla X (for example) equipped with a ~25 kW generator and only a ~50 kWh pack could easily make the same ~three hour ~200 mile Winter Tahoe trip non-stop, while a 90 kWh Tesla X BEV would probably have to stop to recharge en-route.

The hypothetical Tesla X50x25, would also cost a lot less than an X90, and due to the lower weight, handle better and have superior efficiency.

As an i3 owner I have to disagree. The Rex is by no means oversized. It runs at three settings/revs and is good for 80% of the cases. But it definitely can fail to keep up under load. So this pretty much says to me it is probably in the sweet spot of wright/power. If it was oversized then it would never fail to keep up.

 

[edatoakrun]

...As an i3 owner I have to disagree. The Rex is by no means oversized. It runs at three settings/revs and is good for 80% of the cases. But it definitely can fail to keep up under load. So this pretty much says to me it is probably in the sweet spot of wright/power. If it was oversized then it would never fail to keep up.

If you're going to post a long quote like you just did would you PLEASE read it first?

The reason any i3 driver who made the trip you copied and pasted in your post would find themselves crawling up highway 80 at ~30 mph in the right lane with a line of really unhappy truckers on his bumper, is not due to limitations placed by the kWh output of the ICE, it is due to the limitations placed on the generator's operation by BMW engineers.

An ICE generator with ~one third the i3s kW output would be completely sufficient to climb over Donner pass (or any other mountain pass in the USA, I expect) at ~70 mph if the BEVx's drivers were allowed to turn it on at the optimal time, long before the battery charge was depleted.

A much smaller generator would produce significantly lower penalties in cost of operation and in the BEVx performance and economy in BEV mode, which probably will account for > 90% of all miles driven by most BEVxs.

 

[epirali]

...As an i3 owner I have to disagree. The Rex is by no means oversized. It runs at three settings/revs and is good for 80% of the cases. But it definitely can fail to keep up under load. So this pretty much says to me it is probably in the sweet spot of wright/power. If it was oversized then it would never fail to keep up.

If you're going to post a long quote like you just did would you PLEASE read it first?

The reason an i3 driver who made the trip you copied and pasted in your post would find themselves crawling up highway 80 at ~30 mph in the right lane with a line of really unhappy truckers on his bumper, is not due to limitations placed by the kWh output of the ICE, it is due to the limitations placed on its operation by BMW engineers.

An ICE generator with ~one third the I-3s kW output would be completely sufficient to climb over Donner pass at ~70 mph if the driver were allowed to turn it on at the optimal time, long before the battery charge was depleted.

Ok sorry about missing the point. I am confused because nothing I have seen says there is an artificial output limit. Can you point that out to me please? How is the Rex crippled? If you are talking about the SOC hold that is only a temporary fix and doesn't really mean a Rex with 1/3 output is sufficient for extended driving.