EPA figures for i3 EV revealed

FWIW: To get 98 MPGe , a non hypermiling Chevy Volt gets about 3.5 miles per Kilowatt hour of charge.

 

Too bad CARB's rules are putting hindering limits on when the range extender can fire up for a BEVx.

 

I calculate under 3 miles per kWh in the battery:

33,700 Wh per gallon
33,700/98 = 344 Wh/mile

1000/344 = 2.90 miles per kWh

 

BMW i3 REx Gets Official EPA Rating – Electric Range Of 72 Miles, Gas Only MPG Is 39

 

My arithmetic says the usable part of the battery is ~ 22 kWh.
Anybody know the nominal capacity ?

 

BMW i3 Confirmed as Most Efficient EV Yet

 

Thanks, but that table has errors.

Multiply Miles_per_kWh * Battery_capacity, which = range
If the "battery_capacity" is nominal, the result should be greater than reported; and if the "battery capacity" is that amount used from 'full' to 'empty' (usable), the result should equal the range reported.

In the Case of the i3, 18.8*3.7 = 69.56 miles -- something is wrong. I think the author started from the EPA reported kWh/100 miles number, but that includes wall charging losses. If we correct for the wall charging, we end up back at 22 kWh usable.

I checked a few other cars the same way and found errors too, although to different degrees.

 

In the following story, a Tony Williams led a group to study the 2012 Nissan Leaf were tested to determine the range and energy efficiency. His study suggested that the usable power capacity of the HV battery until turtle mode is 21.38 KwH and the energy efficiency to be about 4 miles/KwH with a range of 85 miles at a constant 62 mph on a flat road with no climate control on. This study was conducted to determine the nature if any of battery capacity loss of Nissan Leaf due to high driving temperature environments.

Battery Capacity Loss - Electric Vehicle Wiki

I'm sure that the BMW EV provides something similar in performance. Fwiw the faster recharging option with the higher voltage-current levels have lower battery recharging losses. The better the thermal management of the HV battery - the more power you can squeeze out of a battery - since extreme temperatures is what makes a battery go wacko. As far as how many Miles per kilowatt-hour(electric power stored) - the general Physics of EV energy efficiency is that as the curb weight drops the fuel efficiency gets better.

 

I think this needs recalculating...

3.7 miles/kWh includes wall charging, so the battery miles/kWh = 3.7/0.85 = 4.3523 miles/kWh.
Range is 81 miles, so max usable battery is 81/4.3523 = 18.6 kWh

 

15% charging loss seems high!

 

15% is pretty standard for 240 Volt.
110 is a bit higher.

 

I think 8% is the norm, but it depends on the car. For those with active thermal management, the energy used to keep the battery within the optimal temperature range is counted as part of the charging losses.

 

the range and energy efficiency of an EV is affected from a number of factors:


* During recharging, there is a power transmission loss-cost between the electric utility's/source generator and the power plug-wall outlet.
* During recharging, The power -thermal loss as the electricity goes through the EV inverter-recharger to the battery
* When the EV is parked and not is not being used, the battery itself can lose charge over time - partly due to the battery and partly due to a *phantom* drain necessary to maintain the onboard computers - the lost is cumulative and over time can drain the battery if the EV is not used over a long period of time.
* When the EV is moving, the battery (thermal-current level) management overhead uses some of the battery power.
* When the EV is moving, Most modern electric motor have a very small power loss in converting electricity to kinetic energy but it is still there.
* Any time the EV is on, if the climate control is used, it can drain battery power signficantly -especially at very cold temperatures.

still an EV like a Nissan Leaf is very energy efficient... it just doesn't go as far as a Prius does

 

I don't think charging losses are important, just mpge and range I mean really from a users POV its just how much electricity they need to have a fuell charge - from the wall, and the range from a full charge. You provided that full information in the table.

I do like how efficient the i3 is, and like the specs. Also BMW is selling the car soon in austin. That's refreshing versus toyota not selling the phv here. With that range extender and liquid cooled pack they should sell more i3s than leafs in texas. That stupidly small gas tank, required by carb to get HOV stickers in California, though will hurt it in most of the country. Common BMW make a texas version with a 5 gallon gas tank.

 

True, but EVs are tempering that rule due to regen. The old rule of thumb for ICE cars was that an X% drop in weight would lead to an X/2 percent improvement in fuel economy. Now that ~ 50% of braking is collected by regen, the improvement in fuel economy is X/4 percent.

The i3 shaved about 20% of weight off the car by using carbon, so city fuel economy improved by about 5% and combined economy by about 2.5%.

Which makes rather obvious that the weight reduction was not done for fuel economy sake, but 0-60 times and passing performance.

 

It would also improve handling performance too. A nimble car would be more fun to drive than a faster barge of a car.

 

Better be as light as possible with these tires, and how about the look?

 

Weight also improves rolling resistance

 

Yep I'm sure the low weight allows those motorcycle tires to grip.

I actually like the look of the tires and wheels, and its functional, they reduce drag and rolling resistance. But to me the car is kind of ugly, and like the leaf this will reduce potential sales. It seems strange that the wheels are so tuned to aero, but the rest of the car has so much higher drag than the active E (cd=0.29 but much larger frontal area). I'm sure some will like the look. Its personal taste. One nice thing about the i3 and i8 platforms, it isn't that expensive to build a second car with very different looks as its cfrp body on frame. The expensive aluminum frame that holds the batteries and motor can stay exactly the same, and cfrp doesn't require much different tooling no matter what it looks like.

The low weight of the cfrp also lowers the cg, which is already good in bevs. The question is if bmw can actually reduce the extra cost enough versus say the aluminum tesla uses or the high strength steel porsch uses. BMW thinks it can, and I doubt we will hear the true cost unless it gets down to say twice the cost of aluminum, and bmw puts out a press release. BMW is sellling the car, but it really is for R&D and marketing (technical leadership).