41 miles per dollar equals 156 mpg for us
Monday was meter reader day for us.
We may not have been totally dedicated to the “fuel” consumption of our LEAF initially, but we became more attuned to its impact as each day passed. We brought home our LEAF on March 25 and first charged it using the 120-volt brick charging unit, as our 240-volt Blink electric vehicle supply equipment (EVSE or wall charging station or charging dock) had not yet been installed. In reviewing our old posts, it seems that with the 120-volt brick, we achieved roughly 3.4 miles per kilowatt hour. As it happens, we’ve run the math since we received our LEAF and calculated a total miles per kilowatt hour of 3.3 using our 240-volt Blink charging dock to date. We mention this not because the range will vary depending on charging method, but because the 120-volt EVSE was not metered in the second meter mentioned below. Let’s take a closer look.
On Monday, our accumulated mileage to date (since March 25 delivery) is 3,833. The kilowatt hour usage reading on our second SDG&E meter is 1,161 kilowatt hours. This includes all electricity provided through the 240-volt Blink EVSE, but none provided through the 120-volt EVSE. Pretty simple math – 3,833 divided by 1,161 provides 3.3 miles per kilowatt hour from the wall. We have never reset the energy setting on our car since new, and it reads 3.5 miles per kilowatt hour. So there is some discrepancy between the two. We don’t really know the reasons why. (Edit: 100% of electricity taken from the wall is not converted to power in the battery just as not all gasoline is converted to power in a gasoline engine. This accounts for at least a portion of this descrepancy.) This difference amounts to about 6%.
We are part of a San Diego Gas & Electric (SDG&E) electric vehicle (EV) experimental rate plan. As such, our super off peak rate (from midnight to 5:00 AM) is roughly $0.075 per kilowatt hour. We generally charge our car during this time frame, using the Blink’s built-in timer. We plug in our car after the last drive of the day and it starts charging at midnight. As our usage varies from day to day, it generally takes two to three hours to bring our LEAF back up to an 80% charge. We generally charge to 80% vs. 100% as we have no need to travel more than an 80% charge will allow, and according to Nissan, battery life is extended with an 80% charge cycle. Currently, these are the only two choices offered by Nissan with the LEAF – 100% or 80%. We have charged (rarely) at the highest rate of $0.35 per kilowatt hour, although we try to minimize that. Also, we have never charged at a publicly available charging station, although we did charge at a friends house on their Blink for an hour or so once.
Getting back to the math – 3.3 miles per kilowatt hour (@ $0.08 – we rounded up to account for the infrequent higher rate charging) equals 41 miles per dollar. In San Diego currently, regular gasoline is $3.80 per gallon. That equates to a cost factor equivalence 156 miles per gallon. But let’s say you were paying the national average rate of $0.11 per kilowatt hour. That would still equate to 30 miles per dollar. Not as impressive perhaps, but that still equates to roughly 114 mpg in San Diego at current gasoline prices.
We stand by our initial assessment – The LEAF is a situationally specific vehicle. It is not right for everyone, but if it is right for your situation, it offers an extremely low cost of operation compared to even an extremely efficient hybrid gasoline-electric vehicle. (Disclaimer – others may get greater or lesser miles per kilowatt range. Our 3.3 miles per kilowatt usage equates to a 100% charged range of (3.3 miles X 24 kilowatt hour battery) 79.2 miles.)
UPDATE (Nov. 18, 2011): In the comments below, indyflick correctly points out our incorrect usage of the term MPGe in our original article (which we have since edited out). Miles Per Gallon Equivalent (MPGe) is an EPA formula that compares the energy equivalence of electricity vs. gasoline. indyflick provides the formula in the comment so I will not repeat it here. Our intent was to show an economic equivalence, versus an energy equivalence. There is an important reason for this distinction. MPGe will not vary. Energy is energy so MPGe will remain constant. In our illustration, we are interested in actual cost of operation, which will vary based on the cost of energy. MPG in a gasoline powered car will vary based on vehicle and driving style, so your fuel costs vary accordingly. Similarly, the cost of operation of an EV will change based on the cost of electricity as well as maintenance costs. Ignoring maintenance costs (which have been nil to date), we meant to focus on our cost to move our LEAF down the road, but especially to compare that cost to that of someone driving a gasoline powered car. We, in error, referred to that as MPGe. We apologize for the confusion.
Thanks for the report. Do you charge exclusively at home? I have 11,500 miles so far and although I don’t keep exact records, I estimate that I charge my LEAF away from my garage more than 50% of the time. This “dilutes” my direct operating cost of electricity considerably…
Tom – you make an interesting point. I hadn’t considered those that charge their LEAF at (currently) no-charge publicly available locations. For those that do, the cost of operation can be significantly less per mile. As you point out, if you charge at these no-charge public locations 50% of the time, your out-of-pocket cost for that electricity is nil. Also, some employers are making charging stations available at work, some of which are also provided at no charge. For those lucky employees, they may have the opportunity of charging for eight (or more) hours at work, thus incurring almost zero cost of energy to operate their electric car.
To answer your first question – yes – we currently charge exclusively at home.
Thanks for the update Ernie. I think I’m missing your point in the first paragraph. Your miles/kWh isn’t affected by Level 1 versus Level 2 charging. It’s affected by driving conditions, how you drive, use of climate control, etc. However, Level 1 versus Level 2 would impact the miles of range per hour of charging.
My second point would be that miles per gallon equivalent (MPGe) isn’t derived from the price, rather it’s derived from the energy. EPA’s MPGe formula assumes 33.7kWh of electricity is equivalent to one gallon of gasoline. So the energy consumption of an EV, during EPA’s five standard drive cycle tests simulating varying driving conditions, is calculated and then, using 33.7kWh, converted into the MPGe statistic. So if an EV completed the drive cycle using 33.7kWh of electricity to go 100 miles then it would have 100 MPGe rating.
Hi indy – Sorry about being unclear. In my opening paragraph, I mentioned that my initial charging was on the 120-volt EVSE because it was not being metered through the second meter, so it was not reflected in the second meter kWh usage to date. I did not make that clear in my article. I did not mean to imply that Level 1 versus Level 2 would impact range.
I see your point about the EPA’s MPGe formula. I should not have used the term MPGe then, as they are basing their formula on energy equivalents. I am basing my evaluation on cost of operation. I will add an update to, and edit my original article, to eliminate this confusion. The point that I was trying to make is this: to operate a gas powered vehicle in San Diego today, the cost of regular gasoline is roughly $3.80 per gallon. Purely on a cost basis, if I am going 41 miles for every dollar that I spend on electricity, my wallet sees this as going the equivalent of (41 miles X $3.80) 155.8 miles for what I would have spent on one gallon of gasoline. I hope that clears up the confusion. MPGe is an energy equivalence measurement. I am more interested in a cost of operation equivalent (realizing that this will vary based on cost of energy vs. EPA’s energy equivalence, which will not).
Today in my LEAF with the Mrs… Left home at 8:00a for breakfast and shopping at Santa Monica Place (42 miles). Charged there back up to 100%. Drove on to Brea (40 miles) for the Nutcracker Boutique (Xmas stuff)… On to downtown LA for the car show (25 miles)… Parked at Downtown Nissan to charge back up to 85% (free parking) and a short walk to the convention center… Then all freeway home… Lots of fun and very friendly people at Downtown Nissan… Total miles in a 12 hour day was 159.5… No gas…
Tom – thanks so much for your input. It points out that Nissan LEAF drivers actually can drive well over 100 miles in a day with appropriate planning and some conveniently located charging docks. Statistics have shown that most drivers (on average) drive 40 miles per day or less. But there are days, such as the one that you just experienced, that might significantly exceed the average use. As the charging station network grows larger, more EV drivers will be comfortable with arranging a day such as yours. Thanks again.
Thanks for the blog post. The difference between what your Blink Charger says you’ve used and what you Leaf thinks its used is the charging loss. Not 100% of the energy that comes out of your charger ends up being stored in the battery. Generally the number is at best 90%, so I’m surprised the difference you’re seeing is only 6%.
I’m up here in Seattle and just hit 6,000 miles in my Leaf. I’ve been keeping track of efficiency like you closely and the Leaf dashboard is saying I’m getting 4.6 miles/kWh. That’s about 75% freeway driving and 25% city driving. Our temperatures are much more moderate up here in Seattle. So far, my efficiency seems to be holding up to fall weather too.
Gary – welcome to Living LEAF. As I was writing this article I did not have the charging efficiency top of mind. You’re absolutely right that there is some charging loss. Glad to hear that your LEAF is serving you well as the temperature is dropping. I will edit my original article to incorporate the charging loss.
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