to REx or not to REx ?

[FrancisJeffries]

The i3 REx is the best compromise for us and for many others too.

Include me in that list! (I find that I can do at least 90 miles - not 45 miles as quoted by an American poster - between petrol fills on the motorways; and I'm not hanging about!)

 

[ironsia]

I think Surge may not have recognised that the cost/benefit for those of us with European-spec REx is different, as we don't have the hill-climb compromise that has so troubled some in N America.
I'm with those who say they can drive far more electric miles, just because they have the REx, and for relatively rare long journeys will refill the tank repeatedly if DC fast charge is unavailable. Many European family units only have one car, and that changes the cost/benefit, too.

 

[jadnashuanh]

Europe has installed LOTS more CCS units than in the USA, and, consider this...there are a lot of states in the USA that are larger than the whole of the UK...distances matter. Europe is quite compact in relationship. But still, stopping every couple of hours for a recharge AND a refuel isn't anywhere as convenient as chugging along on an efficient ICE (on mine, I can go about 500-miles on a tank), where I don't have to worry if I'll make it to the next refueling station. There are roads in the USA where you may not find a charge station OR a gas station in beyond the range of the REx - there are some REALLY open spaces. I really doubt that is even possible in Europe, at least Western Europe where the population density is so great. So, you have to consider all of the factors...IMHO, the REx doesn't replace an ICE for the majority of Americans, no matter how they implement turning the thing on. Yes, you can make it work, but it is a major compromise. That may change if and when CCS are as common as gas stations, but I doubt that will ever happen in the near term. England seems much further ahead on this, but then, the area is SO much smaller, it won't take as many so that people aren't far from one.

 

[Jeffj]

This has turned into a religious argument, which, IMHO, doesn't really advance the original topic.

For my own decision tree (which is all that really matters to me), I'm getting an i3 because I want to move to an electric vehicle, and I want to have one that thrills me. I drive a 14 year old F-150 right now that is staying in the family, since we need it to pull a horse trailer, haul hay, etc. By moving to an electric, I can replace 95% of the mileage that I'm putting on my truck with electric miles. For those times where the AER is not sufficient (and I'm not hauling a horse trailer), I'm opting to get the REx which will still enable me to make the vast majority of those trips using electric (the alternative being to not take the i3 and drive my truck instead). I can't see any scenario in this case where the statement "If the BEV isn't for you, then the REx likely isn't for you either" has any applicability for me.

 

[ultraturtle]

Surge,

I enjoy our occasional skirmishes on this topic. It ups both our games.

Oh Ultraturtle, you make me boot up my laptop to address the inaccuracies in your above post!

Differences of opinion? Yes. Inaccuracies? Let's see...

Your views are "ultra-" tainted, I suspect, to justify your decision.

Let me try and present a more balanced perspective.
(For background, I'm an automotive engineer, having worked for Toyota in Japan, GM and Ford in NA, and a small silicon valley auto startup. Note: I'm not a Tesla fan)

I can barely muster enough intelligence to tie my own shoes and therefore tend to rely on fact and simple observation.

While I disagree with most of your opinions, I respect them.

Still, they are only opinions.

Summing up and updating reasons to REx from a previous thread (http://www.mybmwi3.com/forum/posting.php?mode=edit&f=2&p=6778):

• 1. It is incredibly inexpensive. You cannot find a liquid cooled, highly efficient, staggeringly low emission 34 hp gen-set anywhere for $3,850, much less one that imposes no volume penalty, and integrates seamlessly with the i3's electrical system.
  
  Actually, you can get a whole house generator for this price...
  
  Not an accurate observation. The REx contains a 25 kW liquid cooled gen-set (page 1 of the W20 Engine Technical Training document). Liquid cooled 25kW whole-house gen-sets from a reputable manufacturer start at $8,399 MSRP (discounted to ~$8,231), weigh more than 3 times as much and occupy roughly 10 times the volume of the entire REx system (http://www.generac.com/all-products...nerators/guardian-series/guardian-series-25kw). They do not come close to the Super ultra low emission vehicle (SULEV) and zero evaporative emissions compliance required by CARB as does the REx.
  
  The REx system is a marvel of modern engineering, and (to me) one of the most appealling features of the i3.
  
  2. It imposes a negligible weight penalty, slowing the zero to sixty time by only 0.8 seconds (still quicker than any other EV except the Teslas), and increasing the fuel consumption to carry the additional weight by only 4.65% (seehttp://www.bmw.com/com/en/newvehicles/i/i3/2013/showroom/technical_data.html#m=i3_range_extender) or roughly $129 (assuming $0.11/kWh) over the course of 100,000 miles
  
  0.8 seconds to 60 is HUGE. A Porsche 911 costs $15K more for 0.3 seconds improvement. You can definitely feel 0.3 seconds. A forum member has both the BEV and the REx, and he said there is a considerable difference in acceleration. You don't buy an i3 for acceleration, although a BMW should be sprightly; but just wanted to clear the air on this topic.
  The point is that the weight penalty is about 10%. That's a big deal, especially in a car where the engineers did the best they could to shave off as much weight as possible.
  
  The fuel consumption increase of 4.65% is optimistic. Factor in winter conditions when the heat pump in the BEV is much more efficient at heating the cabin and it's more like 7-10% (see my earlier posts).
  
  4.65% is a measurement. 7-10% is an opinion. The heat pump system in the BEV differs from the heat pump system in the REx only by the insertion of an additional heat exchanger between the coolant pump and electric heating element. (see http://www.mybmwi3.com/forum/viewtopic.php?f=2&t=1776). While I have no doubt that this increases efficiency of the heat pump system somewhat in a narrow range of outside air temperatures, I find it highly unlikely it would save 2-5 percent of total electricity consumption, as you assert.
  
  3. It eliminates the cost to rent or own and maintain a gasoline fueled vehicle for trips beyond a BEVs electric range.
  
  No way! Extremely wishful thinking. You're talking about ~60 miles of additional range (in North America). If your trip is longer than 80 + 60 miles, you still need another car… unless you want to deal with severe power loss at normal highway speeds or when climbing a grade with the REx running.
  
  It is now your choice to either deal with the limitations placed on the REx in North America, or spend a little time and $20 to enable the Hold Charge feature. As many folks have posted on this forum, the i3 REx is a delightful road trip car. Its comfortable, upright seating, spacious interior, and gobs of practical storage space make it one of the most pleasant rides I've experienced.
  
  For a 330 mile trip I take on occasion, I now stop only 1 additional time for gas. I go 90 miles (~20 miles to bring SOC down to 75% to engage the REX, then another ~70 miles to fuel depletion), then two more 80 mile legs (~70 miles to fuel depletion, then ~10 miles on battery), with the final 80 miles using gasoline for 50 miles, then depleting the final 30 miles of electric range. At no time during the entire trip do I have less than full power available to pass or climb as long as I want, nor do I ever have less than 20 miles of either gasoline or battery charge in reserve.
  
  4. It eliminates both the embedded and produced pollution caused by renting or owning a gasoline fueled vehicle for trips beyond a BEVs electric range.
  
  No. See #3.
  Yes. See #3.
  
  5. It allows for a greater ratio of EV to gasoline powered driving for any given size battery bank:
  • - For EV only trips, it allows for full use of the battery's capacity, as the driver need not hold any EV range in reserve
    
    No, again. Because the REx starts with 6-7% of battery level remaining. So you're not going to use that last 6-7%, unless you really like to live on the wild side and run the gas tank dry. But this is not healthy for a gas engine, and if you had this personality, you would be comfortable with the BEV
    
    When to engage the REx is now your choice. You choose 6-7%, I can choose any value up to 75%. I believe my deliberate selection of a higher SOC value to be the wiser of the two as it not only guarantees that full power will always be available, but lets me use the full capacity of the fuel tank, leaving plenty of battery reserve to hunt for a gas station.
    
    - For trips beyond the range of a BEV, it allows for not only EV use, but use of the the battery pack's full capacity. Consider a trip of 110 miles, only 100 of which could be reached by a BEV in its most economical mode. The BEV would stay in the garage, and the gasoline powered vehicle would travel the full 110 miles on gasoline only. A REx would be able to travel approximately 90 miles on electrical power, and need to travel only 20 miles using gasoline. 82% electric beats 0% electric.
  
  Not quite right, because a true hybrid like a Prius is far more fuel efficient than running on REx.
  You are picking a REx-ideal range of 110 miles. Why? Why not the average length of an American road-trip, which is far more than 110 miles. A Prius is going to be about 50% more efficient than running on the REx.
  
  Use any distance you want. The math still works. For a 300 mile trip, 30% electric still beats 0% electric. The Prius is 28% more efficient than the i3 REx operating on gasoline, but it is not always available. We are a two car, two driver family, and sometimes both of us need to be somewhere outside of the range of an i3 BEV. We would need to endure the expense, embedded pollution, and lower total electric mile potential of a third car powered by ICE if we chose to purchase a BEV rather than a REx. On a cost basis, the breakeven point between the i3 REx and the Plug-In Prius (PiP) is about 139 miles at today's gasoline and electric prices:
  
  
  
  
  
  and about 109 miles on the basis of greenhouse gasses emitted:
  
  
  
  
  
  so when travelling together, we take the i3 for trips under ~ 110 miles, and the PiP when traveling farther..
  
  6. In many parts of the world, including much of the United States, well to wheel emissions per mile for an i3 REx operating on electricity are less than that of the lowest emission gasoline alternative, the Toyota Plug-In Prius (http://assets.climatecentral.org/pdfs/ClimateFriendlyCarsReport_Final.pdf). The greater amount of electric driving enabled by the REx (see point #5) makes it the more environmentally friendly choice than the combination of a BEV and an ICE vehicle in a great many places. The REx advantage is greater in areas of cleaner electrical generation (typically where a lower percentage of grid electricity comes from coal). If your solar array has excess capacity, the REx advantage is even greater.
  
  7. A BEV is limited to travel only between charging opportunities, making most trips outside of a roughly 30 mile radius inconvenient (3.5 hour wait to charge, although a 30 to 40 minute DC option is available to a tiny percentage of us), and many trips impossible (no realistic charging opportunity). A REx can travel pretty much from any point on a map to any other point on the map conveniently with only a few minute stop for fuel every hour or so.
  
  On the highway you'll be refueling the REx every 45 minutes. Hardly useful.
  
  That's your choice. I prefer to refuel every 70 minutes, after depleting the useable gasoline fuel, and tapping about 10 miles of electric range looking for a gas station.
  
  8. The REx offers the flexibility to change plans as situations change. An unexpected errand that would be impossible for a BEV to include in its planned range for the day would not even be a second thought for a REx
  
  True - but the key word is "limited" flexibility. The REx adds very limited flexibility, at a big cost and weight penalty.
  
  "Big cost"? Not at all. $3,850 is far less expensive than owning, maintaining, and insuring a separate ICE vehicle for trips beyond the range of a BEV. As for weight, 265 lbs is the weight of an average American adult male plus 69 lbs of his stuff. Carry him as a passenger in a BEV, and it would have the same performance and efficiency as a REx.
  
  9. Certified morons like myself occasionally forget to plug the car in at night. A REx would get me to work the next day with no issues, whereas doing the same with a BEV would cost me over $150 in cab fare.

Can't help you there. Do you forget to plug in your phone too? What do you do in those cases?!

You got me on this one. I am a moron, but am self-aware, so I compensate when I can. I carry extra batteries for my phone, but believe it impractical to carry a spare battery for my car.

And from another post on the same thread:

• A decision to purchase a BEV would best be based on the minimum range requirement considering the worst case scenario, which would be the coldest temperature on the last day of either ownership or battery replacement. In my case the assumption that an initial range capacity of 75 miles at 60% highway speeds in fair temperatures will deteriorate to a level greater than the 58 mile range I need 10 years, and 100,000 miles down the road at 25 degrees F might logically drive me toward purchasing a BEV if I believed that temperature, mileage, and time erosion of that capacity to be less than 22%, but the 9 factors I listed made the decision to go with the REx an easy one.

No, no, no… This is wrong decision theory.
You don't buy a shoe based on the absolute worst case scenario. If you did, we would all have steel-toed, Goodyear-soled, knee-high patent leather boots.
It is not correct to base decisions on the absolute worst case. Why?
Because 99.9% of the time you are driving around in a compromise.

We both compromise. You compromise by dealing with the expense, inefficiency, maintenance, embedded and operating pollution of a separate ICE vehicle, which when combined with your BEV, limits you to fewer electric miles than could be achieved by a REx. I compromise by carrying a bit more weight, and consuming about 5% more energy per mile when doing so.

And for what it's worth, the REx is a HYBRID, in every sense of the word.

Agree 100%. That's the beauty of it - see reasons 1 thru 9 above.

You are not "born electric" when you buy a REx. You have a car with a GASOLINE engine and fuel filler cap!

I'm not bashing the REx at all. I just want people to understand that it's a big compromise, and that if the BEV isn't for you, then the REx likely isn't either. It's a psychological placebo with limited benefit.

I still do not understand why folks entertain the discussion of BEV v REx i3. The real choice is between BEV at all (Nissan LEAF, Tesla Model S, BMW i3 BEV, compliance car...) vs a Range Extended Electric Vehicle, also known as a Plug-in Hybrid Electric Vehicle (PHEV) - (Chevy Volt, Toyota Prius Plug-In, BMW i3 REx, compliance car ...). They are very different categories of vehicle for very different needs. I suppose it keeps coming up simply because the i3 BEV is the finest BEV currently available for sale, and the i3 REx is the finest PHEV.

For what it's worth, the BMW i3 REx at 117 MPGe is more efficient than any "pure" EV currently for sale other than the BMW i3 BEV (124 MPGe) and two less than desirable compliance cars - the Chevy Spark EV (119 MPGe) and the Honda Fit EV (118 MPGe). Pretty remarkable.