For those discussing kWh from the dash, vs from the wall, vs what you pay in electricity:
1. There is a common effect in electronics that the higher the voltage of the source the more efficient the device works. I've seen this in computer power supply reviews at SPCR and other sites.
2. The efficiency of my cars charger was tested thoroughly at 120V and 208V but not at 240V in this report
http://avt.inel.gov/pdf/fsev/SteadyS...on2012Leaf.pdf
You'll notice a huge jump in efficiency from 120V to 208V, I expect there is a smaller but still noticeable jump in efficiency at 240V.
I'm also assuming that the curve for efficiency drops off above 3KW if we had the data for 240V.
For rough untested math I'm assuming I'm getting better than 90% efficiency when I charge at 240V at home. The evse I use shows volts and amps when plugged into the wall and with or without charging load. I commonly see 240-242V when the electrical load is low in my house/neighborhood. I have seen it sag to 238 on a hot day with the house AC running. While I can charge at 16a requested, I have the evse limited to 14a based on the curve in the PDF. In reality it seems the car maxes out .5a less than I limit with the EVSE (as in I see 15.5a x 240V when the EVSE offers the car 16a x 240v and I see 13.5a x 240V when the EVSE offers 14a x 240V).
I never log the power used from the wall. It's easier to use the OBDII/leafspy method to see power in the battery and assume the 90% efficiency for easy math. In reality losses may be higher and actual power from the wall to battery efficiency may be in the 86-90% range. With electricity as cheap as it is I don't worry much about the 0-4% possible error in my math.
3. I'm in the camp that believes that the month service charge shouldn't be included in cost per mile or total cost of ownership math but for those that want to know it I have no problem showing the math both ways. It'll be clear that it's a minor factor though.
I have 70 months of electric bills for this house in my spreadsheet and 61 months of electric bills for my previous residence in another tab. The tax rate hasn't changed during that time but the minimum bill (aka monthly service charge) has. I didn't track the actual minimum at first but my cost per kWh column in the spread sheet is total bill / units and that includes tax, service charges, and any other fee they can dream up.
Minimum Bill changes
$6.09 2009?
$8.00 7-2010
$10.00 6-2011
$11.00 11-2011
$12.00 11-2012
$13.00 11-2013
$14.00 8-2014
Residential Electric Rate
Cost per Kilowatt Hour (Cents) as of 5/1/15
Single Family Dwelling 8.879
The most I paid per kWh was
May 2014 $75.66 684 kWh $0.1106 per
The least I paid recently was
Jan 2015 $112.48 1154 kWh $0.0975 per
and for a 1 year and 3 year average I have
Trailing 12 AVG $92.90 905 kWh $0.1033 per
Trailing 36 AVG $93.47 918 kWh $0.1028 per
those averages do NOT include any car charging yet. Using the 12 month average frozen at this point will be a nice comparison come 11.x months from now when I have that 12th new bill in hand.
honestly it doesn't change my math materially vs a gas car no matter if I use 9 cents, 10 cents, or 11 cents per kWh. I often find myself using anything in the 9-11 cent range as close enough if someone else started at that. Sure it could swing the math by 20% but when the cost per mile is roughly 2 cents who cares if it should be 2.1 or 2.3 instead? Anyway I do the math its cheaper per mile than any car I've ever had.
I expect my kWh consumption to rise slightly but not much. Reasons it might not rise include
A. new energy star roofing reducing my AC usage
B. LED bulbs replacing CFLs reducing direct consumption and my AC usage
C. retiring a tube TV that saw nightly use for an LCD that will draw less (direct and AC again)
I want to put more insulation in the attic but I have mods to the car that I want to do before that and some plumbing/tile work that needs to be done.
Oh but what is my cost per mile? Well at best case of 5 miles per kWh, 90% efficiency charging, and 8.9 cents per kWh I'm right at 1.98 cents per mile. At worst case of 4 miles per kWh, 87% efficiency charging, and 11.1 cents per kWh I'm near 3.19 cents per mile.
cost per mile between 1.98 and 3.19 cents if I charge at home all the time. But I don't, I charge at work on L1 getting about 1/4 of my charge for free. I don't do much unexpected driving so my average will be lowered to 1.5 to 2.4 cents per mile after free charging.
I'll spend $30 bucks a year on cabin air filters and windshield wipers. I'll spend several hundred every few years on tires. Even after all that I think it'd be fair to say I can get my cost per mile under 2 cents ignoring the initial purchase price of $9000 + tax and tags.
I ignore those for now because I paid a similar price for my Prius a few years back and so I cancel that out for the comparison. My Prius still gets oil changes, air filter, cabin air filter, wipers, tires. The oil changes being the only one that stands out for the math comparison.
I get about 60 mpg on the Prius for easy math and pay about $2.50 for 100% gas, something like 4.2 cents per mile after oil changes.
Assuming no surprises on repairs for the Leaf I expect the cost per mile to always favor the Leaf with the comparison currently at
~2 cents per mile Leaf (around $0.10 per kWh)
~4 cents per mile Prius (around $2.50 per gallon)
with my costs in TN and assuming gas to kWh pricing stays in the ballpark of the current ratio of 25 to 1.