Calculating electricity expense

[Boourns]

I am trying to figure out how much my electricity bill will go up if I buy a Leaf. Here's what I have calculated. Just want to make sure I'm doing this right:

Efficiency at wall: 4.2 mi/kWh (using this as a conservative estimate for the first few weeks until I get better at driving efficiently)
Miles driven per week: 185 (793 miles per 30-day month)
Cost of my electricity: .11/kWh

That comes out to about 189 kWh for a cost of $20.77 per month. Does that about line up with what you guys spend? That is so much lower than I anticipated. Am I forgetting anything?

I think my ah-ha light just went on. :idea: I spend about $120 a month on gas for my current ICE vehicle IF I can find premium for $3.65/gal.

In related news I'm driving a Leaf for the first time this Saturday. Very excited.

 

[surfingslovak]

Please divide the target energy economy you expect to see on the dash by 0.85. The total wall-to-wheels efficiency is about 80%.

 

[Boomer23]

You did a pretty good job, but you're over estimating your mi/kWh measured at the wall. Charging is only about 85% efficient at 240 volts and less efficient at 110 volts. With my 2013 LEAF SL (with the 17 inch wheels) I'm getting about 3.4 mi/kWh measured at the wall, average for last month. This will vary of course based on your driving speeds and how aggressively you drive. My figures are based on mostly surface streets with less than 10% freeway driving.

Good luck, and enjoy your amazing new ride!

 

[Boourns]

Thanks for the corrections. At 85% efficiency that's still only ~$24.43 a month! Now I see why you guys are so passionate about this stuff.

 

[dgpcolorado]

[I see that others have beat me to it, but I'll post this anyway.]

Your numbers are reasonable although 4.2 miles/kWh from the wall might be a bit optimistic if you drive at high speeds. To get a better idea of what sort of mileage you can expect at various speeds, check out Tony Williams' Range Chart.

You can assume about 75% efficiency if you charge at Level 1 (120 Volts) and 86% if you charge at Level 2 (240 Volts). If you limit charging to 80% or if you get the charge package with 6.0 kW charger, you might see efficiencies around 90%. Examples:

Drive at 60 mph and charge at Level 1: 3.9 miles/kWh x 0.75 = 2.9 miles/kWh from the wall

Drive at 35 mph and charge at Level 2: 6.3 x 0.86 = 5.4 miles/kWh from the wall

And so forth; those numbers are based on ~70ºF. Your mileage will be lower in cooler weather and a bit more in warmer weather. Rain, wind and use of the climate control system can reduce mileage somewhat.

 

[davewill]

Thanks for the corrections. At 85% efficiency that's still only ~$24.43 a month! Now I see why you guys are so passionate about this stuff.

It gets even better with rooftop solar. Can you say, "No fuel expense?"

 

[walterbays]

That comes out to about 189 kWh for a cost of $20.77 per month. Does that about line up with what you guys spend? That is so much lower than I anticipated.

Charging is only about 85% efficient at 240 volts

So say $24.44/mo which is still much less than your $120/mo for gas.

Am I forgetting anything?

Battery replacement cost which will almost surely be higher than electricity cost. We don't know what the cost will be because Nissan refuses to say. But they have put an upper bound on the cost with their $100/mo battery rental program.

So you'll start off saving big, paying $24 versus $120. Eventually your battery will give out and you'll be pretty much breaking even, paying $124/mo versus $120. If you guess your battery will last 5 years and you'll keep the car 10 years then the upper bound on your cost averaged over 10 years is $50/mo, so you're looking at $74/mo versus $120/mo.

But the reason Nissan refuses to give a battery price is probably because they're betting on a technology breakthrough to radically reduce the cost, increase the capacity, and/or increase the longevity. If you guess you'll replace your battery at 5 years for an exchange price of $5000, drive another 5 years, and have a residual battery value of $2000, then your average monthly cost is $25. If that bet is right then your total for electricity plus battery will be $49/mo versus $120/mo.

 

[Boourns]

^ Good points, and given my climate (Texas), exactly why I'll be leasing for 24 months.

 

[dgpcolorado]

^ Good points, and given my climate (Texas), exactly why I'll be leasing for 24 months.

And that is a good decision on your part. Have fun with the LEAF, I certainly have.

 

[Galiano]

I have had my Leaf for about 10 days now so I still have a lot to learn. Could someone please explain what " at the wall" means ?

According to the onboard stats, I seem to be getting 7 km per Kwh. We pay 6.9 cents per Kwh. Am I correct in thinking my cost per kilometer is about 1 cent ? If that's the case I am thrilled, or am I way out to lunch ?

 

[DarkStar]

Thanks for the corrections. At 85% efficiency that's still only ~$24.43 a month! Now I see why you guys are so passionate about this stuff.

Heck, round up to $30 per month just in case... And it's still a great deal!

 

[smkettner]

I went from $300 in gas to $30 in electric.
Easy to underestimate miles because the other car is now the gas hog and will be driven less.

 

[Boomer23]

I have had my Leaf for about 10 days now so I still have a lot to learn. Could someone please explain what " at the wall" means ?

According to the onboard stats, I seem to be getting 7 km per Kwh. We pay 6.9 cents per Kwh. Am I correct in thinking my cost per kilometer is about 1 cent ? If that's the case I am thrilled, or am I way out to lunch ?

At the wall means power use measured from the wall plug or power panel rather than measured from within the car's battery pack. This is relevant because the charging process takes some energy. Level 2 charging (240 volt) on the LEAF is about 85% efficient, so you are using up 15% of your power from the wall in the charging process. If you see someone mention that they are driving at 4 mi/kWh measured from the car's dash display, they are really getting about 3.4 mi/kWh from the wall.

You can apply that factor to your indicated km/kWh figure to calculate how much you are actually spending. Let's see 7 x .85 = about 6 km/kWh. Not bad.

Charging at Level 1 (115 v regular wall outlet) is said to be a bit less efficient than Level 2. I'm not sure of the efficiency figure.

Cheers.

 

[cwerdna]

Please divide the target energy economy you expect to see on the dash by 0.85. The total wall-to-wheels efficiency is about 80%.

Huh? Don't you mean multiply?

If multiplying by 0.85, 4 miles/kwh on the dash would be 3.4 miles/kwh.

 

[dgpcolorado]

I have had my Leaf for about 10 days now so I still have a lot to learn. Could someone please explain what " at the wall" means ?

According to the onboard stats, I seem to be getting 7 km per Kwh. We pay 6.9 cents per Kwh. Am I correct in thinking my cost per kilometer is about 1 cent ? If that's the case I am thrilled, or am I way out to lunch ?

Good question. "At the wall" refers to measuring electricity use from the wall, using a meter of some sort (see the link in my signature). The reason this is significant is because there are losses when charging a LEAF in terms of how much electricity makes it to the battery. Also, measuring electricity use from the battery is subject to some errors, so it may not be very precise. If you really want to know how much electricity you use to drive a LEAF you need to measure it at the wall or estimate it from the electricity used in the car corrected for estimated charging losses. Level 1 charging at 120 Volts, 12 Amps is thought to be about 75% efficient. Level 2 charging at 240 Volts, 16 Amps has been reported by a study to be 86% efficient. Level 2 charging at 240 Volts, 27.5 Amps (6.6 kW) can be expected to be a bit more efficient. Preheating while plugged-in will lower efficiency. Charging to 80% instead of 100% can be expected to be slightly more efficient.

So, if you are charging at Level 1 and getting 7 km/kWh you are likely getting about 5.25 km/kWh from the wall. If you charge at Level 2 you are likely getting about 6 km/kWh from the wall (or a bit more if you use 6.6 kW charging). You can use those numbers to estimate your cost of electricity.

 

[donald]

Heck, round up to $30 per month just in case... And it's still a great deal!

.. compared with a modern 85 mpg compact Euro-diesel? 9 gal of fuel/mth (in the OP's case)?

The best modern diesels are good competition for EVs. But in my mind diesels lose to EVs on ease and quality of the driving experience, ownership and maintenance, rather than on cost alone.

I lease the battery, here in UK, and overall lifetime costs will be greater than my 60 mpg diesel [other] car (and we pay twice as much for fuel here, too). But that's not really the point - I simply prefer 'EV' now.

 

[johnrhansen]

Even if it ends up costing more, you can feel good because you are now part of the solution instead of the problem. Zero emissions is a good thing!

 

[donald]

Depends where the electricity comes from.

 

[dgpcolorado]

Depends where the electricity comes from.

Perhaps. A lot of the Pacific Northwest and Norway folks have hydropower. And even people in coal power country can usually install solar panels if they want zero emission electricity. A lot of LEAF owners have done that, although it may be less practical in often cloudy places, such as the UK.

There are other benefits from driving electric besides overall emissions; my interest is partly geopolitical. And as a bicycle commuter I particularly despise diesels.

 

[slcleaf]

Can someone give me a formula to calculate the electricity costs to charge the batteries? I called my electric company and they gave me this calculation, which if this is correct, I will be spending $150-$200 a month for electricity.

watts x hours charged per day x days per month x rate (my rate is .09 cents for winter and .11 cents for summer)

I contacted Nissan and they told me to use this formula. (I have the 2013 SL with the 6.6kW on board charger)

6.6 x hours per day charged x electricity rate

Based on these two formulas this is what I would pay for electricity.

6.6 x 8 hours on charge x 30 days x .09(winter rate)=$142.56

I am using the 110-volt charger.

With these figures it isn't any more economical than an economy gasoline car. I am reading that people are paying $20-$60 a month to charge so I don't think these formulas are correct. Any help you can give me will be appreciated. Thank you!