EPA rates Model S at 89MPGe with 85 kWh pack

[Norbert]

Doe anyone know whether the Leaf's 73 EPA mile range is achieved with putting some battery capacity aside, as reserve, and only using perhaps 21 kWh or so, or if it is achieved with the full 24 kWh, also using the reserve ?

 

[Tommy]

Typically the manufacturer runs the numbers them selves and submits them to the EPA. The EPA lab only verifies a small fraction of the vehicles on the market each year. Not sure if the Model S was actually tested by the EPA or not. But given the scenario you can pretty much guarantee that Tesla will have chosen the most efficient charging rate to present the Model S in the best possible light.

Thanks, that was info I wasn't aware of. Currently, it looks like any additional improvements in the mpg-e will likely come from efficiency gains Elon's hinted at with the on-board Model S charger(s)

 

[SoCalGuy]

I don't think that's correct - it should be apples to apples on the basis of the equivalent math above. The Fisker numbers are very close (3-5%), and the delta is within rounding errors. The Model S nums seem off by20% .

 

[Dave EV]

Doe anyone know whether the Leaf's 73 EPA mile range is achieved with putting some battery capacity aside, as reserve, and only using perhaps 21 kWh or so, or if it is achieved with the full 24 kWh, also using the reserve ?

The usable capacity of the Nissan LEAF is around 21 kWh. The EPA test procedures dictate that the car be charged to 100% and run through the test until the car is unable to go fast enough to run through the load profile. It takes around 24-25 kWh from the wall on L2 240V/16A to charge the LEAF from turtle mode to 100%.

 

[stopcrazypp]

I don't think that's correct - it should be apples to apples on the basis of the equivalent math above. The Fisker numbers are very close (3-5%), and the delta is within rounding errors. The Model S nums seem off by20% .

The numbers will vary based on how much actual usable capacity the car has and also the charging efficiency. The established EPA procedure is to measure electricity used at the socket. If the usable capacity percentage is the same as the charging efficiency percentage, the result will be like the Fisker's numbers.
http://www.smidgeindustriesltd.com/leaf/EPA/EPA_test_procedure_for_EVs-PHEVs-1-13-2011.pdf

The 2013 Volt gets 35kWh/100miles. AER is 38 miles. Works out to 13.3kWh to fully charge. 10.8kWh usable. 81.2% charging efficiency.
http://www.thedetroitbureau.com/wp-content/uploads/2012/06/2013-Chevrolet-Volt-window-sticker.jpg

The 2012 Leaf gets 34kWh/100miles. AER is 73 miles. Works out to 24.82kWh to charge. 21kWh usable. 84.6% charging efficiency.
http://www.hypermiler.co.uk/wp-content/uploads/2011/01/nissan-leaf-epa-sticker-photo.jpg

The Fisker gets 65kWh/100miles. AER is 32 miles. Works out to 20.8kWh to charge. 18kWh usable (found the link below). 86.5% charging efficiency. As I said, the actual capacity is 20.1, so 89.6% usage (similar to the charging efficiency) which makes the math seem to work out (but not quite).
http://www.thecarconnection.com/review/1073134_2012-fisker-karma_green_7

 

[jimbakker666]

The base car will start at $64,900 – $57,400 after deducting the federal $7,500 tax credit. A top-line Performance Model, with the big battery, goes for $87,400 after the tax credit.

....

I don't understand how this is allowed to occur. It takes two seconds to look at Tesla's website and see that the base car price this writer is quoting is wrong. It seems more blatant lie than casual oversight and it really annoys me that this guy isn't checking his facts.

Interested to see if Tesla can make the charging scheme more efficient. My money says yes.

 

[richkae]

265 miles per 85kWh battery suggests 32kWh per 100 miles actual performance.
Wall to wheel 38kWh per 100 miles means 84% efficient charging.
Increasing charging efficiency to 91% gets you 35kWh per 100 miles and bumps you to 97mpge from 89.

 

[Todd Burch]

I don't understand how this is allowed to occur. It takes two seconds to look at Tesla's website and see that the base car price this writer is quoting is wrong. It seems more blatant lie than casual oversight and it really annoys me that this guy isn't checking his facts.

Interested to see if Tesla can make the charging scheme more efficient. My money says yes.

Source: Detroit. I don't think it's coincidence that seemingly every "fact" coming out of a Detroit source is wrong, and wrong in a way that casts a negative light on the Model S and Tesla. Some may see my view as cynical...I see it as reality. With the exception of smaller Detroit suppliers providing parts for Tesla, Detroit has every incentive to quell interest in that Silicon Valley company that seems to have developed a high tech vehicle and full manufacturing facility for a fraction of the cost of the big guys.

 

[malcolm]

The biggest factor affecting overall charging efficiency isn't the few percentage points you can squeeze out of the power electronics, it's the overall losses including things like battery cooling. (Is this the reason that the Leaf's figures are better?)

The EPA should make it clear that electricity use also varies with charging power, so that the table would hold (say) eight numbers rather than just four. For example:

Wall Socket Recharging Power kW	City MPGe	Highway MPGe	Combined MPGe	Cost Saving $
2
10

Maybe Tesla can publish something like this in the Model S brochure/manual? They could highlight the row which features the official EPA numbers.

 

[Norbert]

The 2012 Leaf gets 34kWh/100miles. AER is 73 miles. Works out to 24.82kWh to charge. 21kWh usable. 84.6% charging efficiency.
http://www.hypermiler.co.uk/wp-content/uploads/2011/01/nissan-leaf-epa-sticker-photo.jpg

So before using the reserve, the Leaf uses even less than 21 kWh, but the 73 miles range includes the reserve? Do you have a link for this number?

 

[SoCalGuy]

The numbers will vary based on how much actual usable capacity the car has and also the charging efficiency. The established EPA procedure is to measure electricity used at the socket. If the usable capacity percentage is the same as the charging efficiency percentage, the result will be like the Fisker's numbers.
http://www.smidgeindustriesltd.com/leaf/EPA/EPA_test_procedure_for_EVs-PHEVs-1-13-2011.pdf

The 2013 Volt gets 35kWh/100miles. AER is 38 miles. Works out to 13.3kWh to fully charge. 10.8kWh usable. 81.2% charging efficiency.
http://www.thedetroitbureau.com/wp-content/uploads/2012/06/2013-Chevrolet-Volt-window-sticker.jpg

The 2012 Leaf gets 34kWh/100miles. AER is 73 miles. Works out to 24.82kWh to charge. 21kWh usable. 84.6% charging efficiency.
http://www.hypermiler.co.uk/wp-content/uploads/2011/01/nissan-leaf-epa-sticker-photo.jpg

The Fisker gets 65kWh/100miles. AER is 32 miles. Works out to 20.8kWh to charge. 18kWh usable (found the link below). 86.5% charging efficiency. As I said, the actual capacity is 20.1, so 89.6% usage (similar to the charging efficiency) which makes the math seem to work out (but not quite).
http://www.thecarconnection.com/review/1073134_2012-fisker-karma_green_7

Thanks - helpful. When you talk about 'charging efficiency' are you suggesting that there's energy loss between the wall socket and the car's battery i.e. as heat in the cable/plug/onboard charger? I know that each of these cars has a electric unusable reserve amount in the battery to preserve battery life/longevity and prevent bricking (Fisker's is 15%, so the actual A123 battery is 23 kwh but only 20kwh or so is usuable). That said, I would still presume that only the usable amount matters in the MPGe calc since its not like at every 'fill up' you need to replenish this reserve (since its not depleted by the vehicle).

 

[Norbert]

That said, I would still presume that only the usable amount matters in the MPGe calc since its not like at every 'fill up' you need to replenish this reserve (since its not depleted by the vehicle).

The EPA's calculations seem independent of the battery size (used or unused)... they supply a full charge, drive it until it can't hold the required speed anymore, and measure how many kWh are required to re-charge it from there to full (until it stops charging).

 

[stopcrazypp]

So before using the reserve, the Leaf uses even less than 21 kWh, but the 73 miles range includes the reserve? Do you have a link for this number?

Got the number from the Leaf forum (it was measured by one of the members):
http://www.mynissanleaf.com/wiki/index.php?title=Battery,_Charging_System#cite_note-5

At no point does the EPA procedure measure or report the "usable" capacity (it does report the full capacity of the battery), so this data must be taken from the manufacturer or measured by an end user.

 

[stopcrazypp]

Thanks - helpful. When you talk about 'charging efficiency' are you suggesting that there's energy loss between the wall socket and the car's battery i.e. as heat in the cable/plug/onboard charger? I know that each of these cars has a electric unusable reserve amount in the battery to preserve battery life/longevity and prevent bricking (Fisker's is 15%, so the actual A123 battery is 23 kwh but only 20kwh or so is usuable). That said, I would still presume that only the usable amount matters in the MPGe calc since its not like at every 'fill up' you need to replenish this reserve (since its not depleted by the vehicle).

You are correct that the energy is lost as heat in the cable/plug/onboard charger. There's minimal loss from the cable and plug; most of it is from the onboard charger converting 120V or 240V AC electricity from the socket to ~400V DC electricity to charge the battery. The battery also heats up during charging and energy is lost there too. That's why proper ventilation while charging may be necessary if your garage temperatures are high. There's also some loss when drawing electricity from the battery, but that's minimal also.

From the article I link, it appears the production Fisker Karma has a 20.1kWh pack, with 18kWh usable; the 23kWh number was from the pre-production Karma:

Fisker says the Karma uses 18 of the 20.1 kWh in its lithium-ion battery pack

http://www.thecarconnection.com/review/1073134_2012-fisker-karma_green_7

 

[Norbert]

You are correct that the energy is lost as heat in the cable/plug/onboard charger. There's minimal loss from the cable and plug; most of it is from the onboard charger converting 120V or 240V AC electricity from the socket to ~400V DC electricity to charge the battery. That's why proper ventilation while charging may be necessary if your garage temperatures are high. There's also some loss when drawing electricity from the battery, but that's minimal also.

AFAIK, the Model S and Roadster additionally use battery cooling during charging, which also requires energy.

 

[stopcrazypp]

AFAIK, the Model S and Roadster additionally use battery cooling during charging, which also requires energy.

That's true, I added the part about the battery heating up during charging (which is actually a very significant loss besides from the charger conversion loss). For liquid cooled batteries (doesn't apply to Leaf), yes battery cooling also requires additional energy.

 

[malcolm]

For liquid cooled batteries (doesn't apply to Leaf), yes battery cooling also requires additional energy.

Thanks, so all Tesla need to do is publish a "Your charging may also vary your milage" section in online and hard-copy documents.

Ultimately the EPA 5 step test needs to include a standard for recharging (e.g all electric vehicles which can be recharged from a wall socket are recharged at "X" kW)

Then EV manufacturers can optimise their charging systems to get the best results from the test - just like all vehicle makers optimise cars to improve City or Highway test figures.

 

[Dave EV]

Ultimately the EPA 5 step test needs to include a standard for recharging (e.g all electric vehicles which can be recharged from a wall socket are recharged at "X" kW)

Yep - at a minimum it would be nice if the EPA tests at least reported what charge rate was used to get the economy numbers. Ideally, we'd get numbers for a few different common charge rates.