Monthly Electricity Cost/MPG Equivalent

[Boomer23]

I may need to figure another way of reading its electric consumption. I track that stuff through excel spread sheets that I use for my own purposes, and to show people the true cost of driving an EV. Having inaccurate data skew this would be bad.

The LEAF's in-car mi/kWh readings are thought to be accurate (despite the fact that there are two of them, and one is always 0.1 mi/kWh higher than the other because it apparently uses a different algorithm, go figure), but these readings are only battery-to-wheels. It's the Carwings data that is unreliable. You can guesstimate your wall-to-wheels figure by using a charging inefficiency factor of about 15% to 17% for Level 2 charging. But you seem like the same kind of guy that I am, and you want real measured data to put into your spreadsheet. For that you should consider something like a TED (The Energy Detective) or something like it.

I have a TED 5003 system installed in my main power panel. It has three measurement modules, called current transformers, and one of them is dedicated to my EVSE circuit so that I know how much power is being used to charge the car from the power panel. Using an Aerovironment Level 2 EVSE hard wired in my garage, I'm getting about 83% charging efficiency if I compare my charging power usage from the power panel to the battery-to-wheels measurement inside the LEAF.

 

[edatoakrun]

"Boomer23"...The LEAF's in-car mi/kWh readings are thought to be accurate (despite the fact that there are two of them, and one is always 0.1 mi/kWh higher than the other because it apparently uses a different algorithm, go figure), but these readings are only battery-to-wheels. It's the Carwings data that is unreliable...

Why do believe (one or the other) "behind the wheel" or the Nav screen readings to be "accurate"?

Why do you believe updated CW "is unreliable"?

 

[DaveinOlyWA]

"Boomer23"...The LEAF's in-car mi/kWh readings are thought to be accurate (despite the fact that there are two of them, and one is always 0.1 mi/kWh higher than the other because it apparently uses a different algorithm, go figure), but these readings are only battery-to-wheels. It's the Carwings data that is unreliable...

Why do believe (one or the other) "behind the wheel" or the Nav screen readings to be "accurate"?

Why do you believe updated CW "is unreliable"?

the dash reading is from the Car. the MFD (center display) is from Carwings which is .1=.2 miles/kw more "friendly"

several ways to monitor usage. a cheap option for less than $50 for even a novice DIY level project.

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

 

[edatoakrun]

"Boomer23"...The LEAF's in-car mi/kWh readings are thought to be accurate (despite the fact that there are two of them, and one is always 0.1 mi/kWh higher than the other because it apparently uses a different algorithm, go figure), but these readings are only battery-to-wheels. It's the Carwings data that is unreliable...

Why do believe (one or the other) "behind the wheel" or the Nav screen readings to be "accurate"?

Why do you believe updated CW "is unreliable"?

the dash reading is from the Car. the MFD (center display) is from Carwings which is .1=.2 miles/kw more "friendly"

several ways to monitor usage. a cheap option for less than $50 for even a novice DIY level project.

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

Are you saying then, that CW does reliably reflect the Nav screen m/kWh on your LEAF, in all cases?

I am curious about the relatively large reported variation in L2 charging efficiency, from various reports, between about 82% and 90%, IIRC. I've asked before, that those with accurate metering methods, check for variations in efficiency with different temperature and (80% to 100%) charge levels, which might resolve this question.

 

[DaveinOlyWA]

Are you saying then, that CW does reliably reflect the Nav screen m/kWh on your LEAF, in all cases?

no. never have. only stating Carwings under reports distance traveled based on whatever you choose to believe since there is no reason for it. it also overstates efficiency by .1 to .2 miles/kw which seems to contradict the above statement. but there ya go.

i use the dash numbers, reset daily and logged

I am curious about the relatively large reported variation in L2 charging efficiency, from various reports, between about 82% and 90%, IIRC. I've asked before, that those with accurate metering methods, check for variations in efficiency with different temperature and (80% to 100%) charge levels, which might resolve this question.

the variance i believe to be primarily caused by methods of measurement. there are only a handful here that can effectively measure 240 power used and most use "devices" i consider suspect. *cough* blink *cough* others had reports from their utilities while others used TED which is the only thing that has verified accuracy.

i was first to report that L1 charging only has an efficiency of 75% +/- 1% and i reproduced that daily for 4 months using Kill a watt which states an accuracy of 99 point several 9's and a 4 or something % which i considered good enough for my purposes.

i then went to an analog meter when i started using Phil's EV mod which is only running at 12 amps. this required averaging efficiency over time, but am convinced that efficiency does vary a little bit so if i avoid charging to 100% i get about 84-85% efficiency which drops to around 83.3 % if charging to 100% which is pretty insignificant.

the difference is primarily the overhead when charging and not efficiency which is probably in the mid 90's for both L1 and L2. the cooling process accounts for the difference so the faster you charge, the less power used by cooling. in the grand scheme of things, the difference in the amount of heat generated between 120 volt, 12 amp and 240 volt 16 amp is probably negligible.

so there ya go. now, i have just provide ammo for FFE fanbois to cry about not having a 6.6 kw charger to increase their charging efficiency

 

[MrIanB]

just got my utility bill and in 3 months of owning my Leaf I have put 1,700 miles for a total of $14.00 dollars. Take that OPEC.

Ian B

 

[LEAFer]

just got my utility bill and in 3 months of owning my Leaf I have put 1,700 miles for a total of $14.00 dollars. Take that OPEC.

Ian B

That's LESS THAN ONE CENT per mile ... :shock: please explain how you do that

 

[DarkStar]

just got my utility bill and in 3 months of owning my Leaf I have put 1,700 miles for a total of $14.00 dollars. Take that OPEC.

Ian B

That's LESS THAN ONE CENT per mile ... :shock: please explain how you do that

In Texas, maybe electricity is about 3.2 cents per kWh?

 

[DaveinOlyWA]

most of Rural Eastern Washington has electricity rates in that area. Douglas County has the lowest at 2 cents per Kwh but several areas are in the 3-4 cent range.

 

[Reddy]

$0.07/kwh here.

 

[MrIanB]

just got my utility bill and in 3 months of owning my Leaf I have put 1,700 miles for a total of $14.00 dollars. Take that OPEC.

Ian B

That's LESS THAN ONE CENT per mile ... :shock: please explain how you do that

Utility bill Jan 31st 2012 was $125.00
1st Leaf bought on 1/20/12, bill for Feb 29th 2012 was $122.00
2nd Leaf bought on 2/10/12, bill for Mar 31st was $137.00

Total miles on both cars 2k. Our utility company does not have time of use rates but it is working on it. Will post their rate once I find the bill to give info on kilowatts.

Ian B

 

[DaveinOlyWA]

just got my utility bill and in 3 months of owning my Leaf I have put 1,700 miles for a total of $14.00 dollars. Take that OPEC.

Ian B

That's LESS THAN ONE CENT per mile ... :shock: please explain how you do that

Utility bill Jan 31st 2012 was $125.00
1st Leaf bought on 1/20/12, bill for Feb 29th 2012 was $122.00
2nd Leaf bought on 2/10/12, bill for Mar 31st was $137.00

Total miles on both cars 2k. Our utility company does not have time of use rates but it is working on it. Will post their rate once I find the bill to give info on kilowatts.

Ian B

1) there is $14 difference PER MONTH, not $14 for 2 months (or maybe 2½ months either way. not 3)

2) one month is 29 days, the other 31

3) it is MUCH darker in Feb than Mar (time change remember) which i would assume would affect lights a bit.

me thinks we need more data. your Leaf is cheap to run but not that cheap. get a meter.

there is a lot of cheap ways to do it.

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

 

[MrIanB]

Ian B[/quote]

1) there is $14 difference PER MONTH, not $14 for 2 months (or maybe 2½ months either way. not 3)

2) one month is 29 days, the other 31

3) it is MUCH darker in Feb than Mar (time change remember) which i would assume would affect lights a bit.

me thinks we need more data. your Leaf is cheap to run but not that cheap. get a meter.

there is a lot of cheap ways to do it.

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

Thanks for your comments but don't see need to buy a meter. I just compare bill before getting first Leaf and the bill with a second Leaf vs how much my bill goes up or down before the cars were bought.

That's just me though. You can measure your way and I measure my way.

Ian B

 

[Rat]

I have a slightly different history that might be useful here since I had the EV9A PG&E rate (TOU) for 5 months before I got the Leaf. That saved me an average of $6.44/mo on electricity (all measuring before taxes) pre-Leaf. After I got the Leaf I am comparing electric bill to the same mo/period before going to the EV rate and the average cost for the 10 months I've had the car is $28.95/ mo or $.06 a mi. for fuel. I don't bother with kwh calculations. Cost to drive it is the only number I am interested in.

Another twist: I think my wife's ICE car cost also dropped because she now takes the Leaf whenever she can do so without inconveniencing me, so her mileage in that car is lower.

 

[TNleaf]

Thanks for your comments but don't see need to buy a meter. I just compare bill before getting first Leaf and the bill with a second Leaf vs how much my bill goes up or down before the cars were bought.

That's just me though. You can measure your way and I measure my way.

Ian B

I'm sorry, but that is probably one of the worst ways to estimate your LEAF's electricity consumption from your utility. The first major issue is that your estimation assumes that you used the same exact electricity from everything in your house month to month (except your LEAF). A change in weather (use of HVAC etc) could throw off the estimates (and due to the fact that your sample size is over the course of a month, it WILL have an impact).

Also, take this for consideration, what would you have done if your bill had gone down? (Let's assume your HVAC in Feb. used more electricity than your LEAF did in March). Your bill in March would have been cheaper... and by your estimation, your LEAF consumed negative electricity! MAGIC! Another thing I've seen people do is compare their bill from year to year for the month. NO, just NO. That's just as bad of a method.

Not trying to be negative, but you really CANNOT estimate your car's electricity usage by your method. In trying to promote this car and EV technology, if you could please refrain from claiming your LEAF's electricity consumption by this method, I would be grateful.

There are affordable devices (meters, CTs, etc) that will accurately measure the electricity consumption of your LEAF when placed on your EVSE.

If you need a free way to estimate, use either of the Economy figures (on the Dash or on the NAV).
-Reset the economy meter
-Reset Trip A or Trip B
-Drive for the month
-Record Economy Figure (miles/kWh) and the Trip meter (miles)
-Electricity used by the LEAF (kWh) = (miles) / (miles/kWh)

Rinse and repeat for each month (or trip).

This method doesn't account for losses in charging (~85%), but it will be MUCH MORE accurate than your method (and easy!).

If you want to account for charging losses and assume 85% efficiency, do the following:

[(miles) / (miles/kWh)] / .85

 

[lpickup]

This method doesn't account for losses in charging (~85%), but it will be MUCH MORE accurate than your method (and easy!).

Right, so just take the final kWh you get and divide by 0.85 to get the electricity used from the wall. There, now you have a more accurate method.

And while I more or less agree with the 0.85 factor, if you frequently charge to 100% you should lower the factor slightly. I just did a short term test on my LEAF comparing the in-car readings with my EVSE's readings and found the factor was between 0.81 and 0.82, however I did one charge to 100% and one to less than 100% during that test, which accounts for my slightly lower reading.

 

[edatoakrun]

"lpickup"...while I more or less agree with the 0.85 factor, if you frequently charge to 100% you should lower the factor slightly. I just did a short term test on my LEAF comparing the in-car readings with my EVSE's readings and found the factor was between 0.81 and 0.82, however I did one charge to 100% and one to less than 100% during that test, which accounts for my slightly lower reading.

So, is the final 20% charge, from 80% to 100% charge, 81% to 82% efficient, or is the entire charge to 100%, at that efficiency, and the final 20% of the charge, at a much lower efficiency?

 

[Bassman]

I use EV9B TOU from PG&E - I charge at work for free and routinely drive 1800 to 1900 miles per month my electrical bill has never exceeded $25,00 per month = about 1.4 cents per mile I currently have nearly 19,000 miles on my LEAF - Love this car!

 

[lpickup]

So, is the final 20% charge, from 80% to 100% charge, 81% to 82% efficient, or is the entire charge to 100%, at that efficiency, and the final 20% of the charge, at a much lower efficiency?

It's just the last X% (I don't know what X is, but I suspect it's less than the last 5 or so percent) and is only because the charging tapers off at the end, but the battery cooling system continues to run (which is overhead).

I don't have exact figures because my EVSE only reports kWh drawn in 15 minute intervals and I don't have any fancy equipment to determine what SOC was reached before the taper off.

Actually maybe the data I have is somewhat meaningful. Here are the tail end of my log from a 100% charging event:

EVSE-1432223	End Of Charge	SET01461100015	249.5	0.68	N	4/1/2012 6:27:55 AM
EVSE-1432223	Charging	     SET01461100015	248.6	0.95	N	4/1/2012 6:15:00 AM
EVSE-1432223	Charging	     SET01461100015	249.2	0.95	N	4/1/2012 6:00:00 AM
EVSE-1432223	Charging	     SET01461100015	248.5	0.95	N	4/1/2012 5:45:00 AM

And here's a non-100% charge:

EVSE-1434885	End Of Charge	SET01461100015	247.8	0.22	N	4/1/2012 6:03:33 PM
EVSE-1434885	Charging	     SET01461100015	247.5	0.94	N	4/1/2012 6:00:00 PM
EVSE-1434885	Charging	     SET01461100015	246.4	0.94	N	4/1/2012 5:45:01 PM
EVSE-1434885	Charging	     SET01461100015	247.3	0.94	N	4/1/2012 5:30:00 PM

The kWh pulled from the wall are very consistent at 0.94-0.95 for each 15 min window. For the non-100% charge, the "final" window was 3.5 minutes long, or 23.3% of the 15 minute interval. Multiplying that by 0.94 kWh I get 0.22 kWh, which is exactly what the last window shows.

The 100% charges have a final window of almost 13 minutes (87%). If it had been running at "full power" the whole time, I should see kWh draw of 0.82, but as you can see, I only got 0.68, or about 83% additional loss in that final block.

I've seen some charts on here that show more detailed current/power draw that illustrate the taper down much better than this rough data.

My original statement, however, was stating that my TOTAL efficiency for 2 charging events (one to 100% and another one NOT to 100%), considering everything, was about 82%. Someday I'll repeat the experiment but strictly to 80% charge and see what the delta is.

 

[DaveinOlyWA]

A few charging at 16 amps are reporting 85-87% which sounds valid since I am charging at 12 amps and measuring 83.3 - 84% consistently. I was also doing 75% with 120 volts 12 amps