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"typical" Miles/KWh figures for a couple scenarios?

Posted: Sat Dec 03, 2011 12:33 am
Hope this hasn't been asked before...

I'm trying to do some ballpark calculations to figure cost per mile (based on my electricity rates) but since I have no Leaf, I don't have a good sense of what are typical miles/kwh figures for driving efficiently vs. very poorly (high speeds, heavy heater or AC usage, lots of stop and go, etc.)

Consumer Reports for example at http://news.consumerreports.org/cars/20 ... re-in.html" onclick="window.open(this.href);return false; reported "On average we consumed 3.16 miles/kWh." Unclear to me if that's "good" or "poor" driving and whether that's energy coming out of the wall (I'd think so).

Can anyone give me a good sense of values like these below?
- hypermiling, trying to go as far as possible
- having a mostly highway trip doing 68-75 mph w/o using AC and heater
- figures that fast driving proponents at http://www.mynissanleaf.com/viewtopic.php?f=27&t=5350" onclick="window.open(this.href);return false; were getting
- driving very poorly for efficiency

Please indicate if these are figures from the trip computer, Carwings or something else (e.g. Kill-A-Watt). I'm actually most interested in the amount of energy coming out of the wall socket when charging at 120 volts (no, I'm not going to install a 240 volt EVSE).

If the figures aren't from out of the wall, what correction factor should apply to trip computer or Carwings results?

Re: "typical" Miles/KWh figures for a couple scenarios?

Posted: Sat Dec 03, 2011 2:40 am
cwerdna wrote:I'm actually most interested in the amount of energy coming out of the wall socket when charging at 120 volts (no, I'm not going to install a 240 volt EVSE).
I don't have any good answers to your questions since I don't have a way to measure my use at the wall, but I would suggest that you reconsider the above decision if you have a choice. My usage is low enough that I typically charge only three or four times a week. I originally expected to live on 120v, and in fact I could if I had to, but ...

It seems to be generally accepted here that 240v charging is 83%-85% efficient, while 120v charging is about 75% efficient. That may not sound like a big difference, but turn the numbers around and think of how much energy you are using. As a rule of thumb, if you need 18 kWh in the battery you will have to pull about 21 kWh from the wall at 240v. Getting the same 18 kWh at 120v means you will need to pull about 24 kWh from the wall!

In other words, your 120v decision is going to waste about 3 kWh for every "tankful" you put in the car.

Ray

Re: "typical" Miles/KWh figures for a couple scenarios?

Posted: Sat Dec 03, 2011 3:30 am
Thanks... do you have a reference for those efficiency percentages?

I most likely plan on leasing and also might be swapping houses w/my parents (long story). I'd rather not spend the expense of a permanently installed 240 volt EVSE and as much as I respect and trust Ingineer (I've met him in person, driven his heavily modded Prius and seen many of his posts here and on Priuschat), I probably won't go w/a his upgrade. :/

The house I live in and might move to are both owned by my parents (they don't live w/me). Let's just say one of them doesn't have a science background and would be paranoid of such modifications (even to the point of becoming very stubborn, incredibly emotional, unwilling to listen, etc. - have been there 2x not long ago about different topics). The other does (but isn't an EE and I'm not an EE either) but still might be paranoid.

Re: "typical" Miles/KWh figures for a couple scenarios?

Posted: Sat Dec 03, 2011 7:45 am
i charged exclusively with 120 volt charging until my move. used Kill a watt and had a rock steady charging efficiency from wall of 75% figured by dividing miles driven per kw from wall over miles/kw from energy screen which would be DC kw from battery which i reset daily.

with the EVSE upgrade running 240 volts at 12 amp (not 16) i am averaging 83.3% efficiency. i am measuring power from wall with a standard meter i installed inline with the 240 volt circuit i am using. nothing but the car is ever plugged into this. long term and short term efficiency has a variance of less than 1%

http://www.mynissanleaf.com/blog.php?u=291&b=92" onclick="window.open(this.href);return false;

Re: "typical" Miles/KWh figures for a couple scenarios?

Posted: Sat Dec 03, 2011 8:20 am
cwerdna wrote:Hope this hasn't been asked before...

I'm trying to do some ballpark calculations to figure cost per mile (based on my electricity rates) but since I have no Leaf, I don't have a good sense of what are typical miles/kwh figures for driving efficiently vs. very poorly (high speeds, heavy heater or AC usage, lots of stop and go, etc.)

Consumer Reports for example at http://news.consumerreports.org/cars/20 ... re-in.html" onclick="window.open(this.href);return false; reported "On average we consumed 3.16 miles/kWh." Unclear to me if that's "good" or "poor" driving and whether that's energy coming out of the wall (I'd think so).

Can anyone give me a good sense of values like these below?
- hypermiling, trying to go as far as possible
- having a mostly highway trip doing 68-75 mph w/o using AC and heater
- figures that fast driving proponents at http://www.mynissanleaf.com/viewtopic.php?f=27&t=5350" onclick="window.open(this.href);return false; were getting
- driving very poorly for efficiency

Please indicate if these are figures from the trip computer, Carwings or something else (e.g. Kill-A-Watt). I'm actually most interested in the amount of energy coming out of the wall socket when charging at 120 volts (no, I'm not going to install a 240 volt EVSE).

If the figures aren't from out of the wall, what correction factor should apply to trip computer or Carwings results?
never got as low as 3.1 miles/kw. did have a handful in the 3.3 to 3.5 range. that was freeway 65 mph heat blasting. this "DC" figures. when considering AC figures you must know efficiency of charging methods

120 volt DC @ 12 amp = 75%
240 volt DC @ 12 amp - 83%
240 volt DC @ 16 amp = 85-88 % (depending on who you talk to. the top two figures i have verified to be accurate. i dont have the 16 amp to test) my "off the cuff" figures says 16 amp should be around 86%

i am getting just under 4 miles / kw. (see sig) so CR figures would be close since i consider my driving to be above average in conservatism and my routes to be more friendly to higher efficiency (since i have chosen the routes specifically for that purpose)

Nissan Engineers drove the Leaf "as inefficiently as possible" per Ghosn interview last month and could not do worse than 50 miles on a charge.

if you plan to do 120 volt charging you must drive less than 50 miles per day. at 63 miles RT, we could not do the Centrailia trip on consecutive days.

correction factor is generally 99%+

due to efficiency and time, i strongly suggest Phils upgrade. more than worth the money. as far as the other options...have yet to see one worth buying (even if given free...many seem to be more of a headache then they are worth)

what we really need is details of your commute, your driving needs, alternative vehicles, etc.

one parting shot. my Prius cost me nearly 3 times more money to drive if NOT including other maintenance costs....

2nd parting shot; nearly 11,000 Electric miles and STILL not an oil change in sight!

Re: "typical" Miles/KWh figures for a couple scenarios?

Posted: Sat Dec 03, 2011 8:24 am
cwerdna wrote: The house I live in and might move to are both owned by my parents (they don't live w/me). Let's just say one of them doesn't have a science background and would be paranoid of such modifications (even to the point of becoming very stubborn, incredibly emotional, unwilling to listen, etc. - have been there 2x not long ago about different topics). The other does (but isn't an EE and I'm not an EE either) but still might be paranoid.
ahh, i can relate. my mother (bless her soul) of Asian decent was very untrusting of things she did not understand and she came from a family of very smart and accomplished people, so she had great intelligence.

Re: "typical" Miles/KWh figures for a couple scenarios?

Posted: Sat Dec 03, 2011 2:06 pm
cwerdna wrote:...
"On average we consumed 3.16 miles/kWh." Unclear to me if that's "good" or "poor" driving and whether that's energy coming out of the wall (I'd think so).

Can anyone give me a good sense of values like these below?
- hypermiling, trying to go as far as possible
...
I do a relatively long commute (78 miles round trip) 2 days out of the week, ~80% by distance is on the highway which has a fair amount of elevation changes the entire way (nearly the whole length of Hwy I-405 in the Puget Sound Area). When I have taken the Leaf lately (w/ light heat and a passenger) I am noticing that I get roughly 3.1 mi/kWh, but that is traveling at normal highway speeds which which cruise at about 65mph periodically going above 70 mph. I would say the consumer reports estimate is about right if they are talking about exclusive highway driving. I can never make the whole trip on one charge.

As for hypermiling; the best I've been able to achieve along that same stretch of road was about 4.3 mi/kWh (no heat, no passenger), for a stretch of about 15 minutes (north-bound between Bellevue and Bothell, for those familiar w/ the area). I was able to even reach speed of 70 mph in that attempt and even getting some regen going downhill (before the UW Bothell campus, for those familiar w/ the area). I wouldn't consider what I was doing aggressive hypermiling and the slip-stream was coming from a van w/ a fairly good cross sectional area, but the level of focus was more than I would want to do every time I get behind the wheel so I don't bother attempting to draft to that level.

Re: "typical" Miles/KWh figures for a couple scenarios?

Posted: Sun Dec 04, 2011 1:02 am
Thanks for the replies.

DaveinOlyWA, your figures are from calculating manually using figures from your electric meter and odomoter, right?

Drivesolo, how about your figures? From the trip computer and not taking into account charging losses? Heh about WA. I've lived in the Eastside for >9 years and just moved back away from there recently...
DaveinOlyWA wrote: what we really need is details of your commute, your driving needs, alternative vehicles, etc.

one parting shot. my Prius cost me nearly 3 times more money to drive if NOT including other maintenance costs....

2nd parting shot; nearly 11,000 Electric miles and STILL not an oil change in sight!
Unfortunately, I don't know the details of my commute yet as I left my job last year and am in between jobs (started looking around, may look to change paths, go back to school, etc.). The problem is where I live (south San Jose) is far from everything. I used to work in Mountain View and it was 24 miles, one way, not including me running errands on the way home. Leaf would be fine for that. If I had to work in say Redwood City or beyond and doing CA freeway speeds (I'd do 68-74 mph on my Prius in 65 mph limit highways and no, I wasn't nearly the fastest) then the Leaf wouldn't work.

If I lived in the Peninsula, then the chance of having no range problem is much lower.

I'd be keeping my 06 Prius as my alternate car for when the Leaf's range won't work or it won't have sufficient charge. For my current driving while not working, the Leaf would be fine for probably 90+% of my trips.

You're blessed by having CHEAP electricity in WA. PSE is cheap compared to ripoff PG&E. Seattle City & Light is even cheaper. I see http://pse.com/aboutpse/Rates/Documents ... ch_007.pdf" onclick="window.open(this.href);return false;. Compare that to the ripoff residential rates at http://www.pge.com/nots/rates/tariffs/electric.shtml" onclick="window.open(this.href);return false;. (TOU billing would likely result in horribly high bills for me as I'm not working right now and at home in the day.) The baselines we get are a joke but somehow, in my last bill, I was able to stay under (baseline was 361 kwh, I used 315). With all the fees and taxes, my 315 kwh cost me \$40.66. If I'd gone over the baseline, then I'd start getting charged the higher tier amounts for the amounts over.

Try plugging in your usage into http://www.pge.com/yourtiers/" onclick="window.open(this.href);return false; and comparing the cost. I'm curious about the cost vs. mine.

For me, w/gas recently bought at \$3.59/gal (pretty cheap for around here) and my Prius' lifetime avg. of ~45 mpg, my cost per mile (strictly from fuel) is just ~7.99 cents/mile.

For a Leaf, If I got 3.16 miles/kwh (CR figures) and assumed 0.20/kwh, it'd be ~6.3 cents/mile. If let's say I got 2.9 miles/kwh and it cost me 0.33276/kwh (highest tier rate), it'd be ~11.47 cents/mile.

Re: "typical" Miles/KWh figures for a couple scenarios?

Posted: Sun Dec 04, 2011 2:40 am
So, let's say you charge at 120v for 12 hours a night. The most you can expect to get is about 17 kWh at the wall, or 13 kWh at the battery. If you intend to drive 70, Tony's chart says your round trip commute will be limited to about 40-45 miles unless you can charge during the day.

But since you and I are in the same PG&E baseline territory X, I know your baseline is 11.7 kWh/day. Assuming you are presently able to stay just at baseline, and that you use the LEAF half as much on non-workdays as workdays, and the 12 hours/night charging for commute, your car is going to pull an average of about 14.7 kWh/day at the wall. This will more than double your baseline, so will put you into tier 4! The car is using all the extra juice, so you need to calculate its cost at the margin.
3.5 kWh in tier 2 @ \$0.139 = \$0.49
8.2 kWh in tier 3 @ \$0.293 = \$2.40
3.0 kWh in tier 4 @ \$0.333 = \$1.00

Your electric bill would go up by nearly \$4/day. The number to focus on is that last one, for tier 4. As I explained earlier, using 120v charging compared to 240v charging you are going to be throwing away 3 kWh for every 18 kWh you get into the battery. Under this scenario you would would be averaging 11 kWh/day, so \$1 * 11/18 = \$0.61/day that you were throwing away. That's \$223/year, nearly the cost of the EVSE upgrade in the first year.

Ray

Re: "typical" Miles/KWh figures for a couple scenarios?

Posted: Sun Dec 04, 2011 3:04 am
^^^
Thanks for the calculations. I'll have to look into that and once I start working, it seems I'd probably better move to TOU billing.

As an FYI, check out Seattle City & Light's rates at http://www.seattle.gov/light/accounts/r ... 22.htm#rsc" onclick="window.open(this.href);return false;. I lived in their service area for a year or so (first extended stay away from PG&E) and was amazed at how low my electric bill was. When I moved to a Puget Sound Energy area, it was a lot more, but still cheap vs. PG&E.

People who live Seattle have it REALLY good when it comes to EV operating costs.