Total Cost of Ownership: Elect vs. Gas Car

[NW-Bound]

If I were to get a Leaf to run errands, I would just plug it into a 115V outlet for trickle charging and not bother with a charging station.

We do not leave the home every day, and then we will also have a 2nd non-EV car for backup.

By the way, our off-peak rate is 7.41c/kWh.

 

[swakyaby]

If I were to get a Leaf to run errands, I would just plug it into a 115V outlet for trickle charging and not bother with a charging station.

+1

 

[TromboneAl]

If I were to get a Leaf to run errands, I would just plug it into a 115V outlet for trickle charging and not bother with a charging station.

We do not leave the home every day, and then we will also have a 2nd non-EV car for backup.

By the way, our off-peak rate is 7.41c/kWh.

The trickle charging is less efficient. There's a baseline usage of 300 watts, so having the charger on for 18 hours means you pay more for a charge.

Also, with Time of Use electricity, our low rate starts at 9 PM. With a trickle, you may need 20 hours of charging, so if you want the car ready at 7 AM, you're going to need to do some charging at 26 and 38 cents per KwH.

7.41c/kWH, wow!

 

[TromboneAl]

Today we drove to Eureka (32 miles away) and some other towns and did a lot of errands. We plugged into a charger, and while we spent an hour eating lunch, it went from 45 miles remaining to 75 miles remaining.

We visited a few other chargers that were near restaurants.

That's from battery to motor, it does not account for charge losses.

Can you give me more info on that?

 

[ERD50]

That's from battery to motor, it does not account for charge losses.

Can you give me more info on that?

As I understand it, the in-car monitors are only telling you how many kWh you use from the battery. But re-charging the battery requires that amount of kWh PLUS the losses of getting that power into the battery.

You can't draw 1 kWh from the wall, charge the battery, and expect 1 kWh out. That would be 100% efficiency, and efficiency of the charger and battery round-trip charge/discharge is likely ~ 85%. So to get 1 kWh out, you need to put 1/85% in, ~ 1.18 kWh in.

That's based on the power from your wall socket. Of course there are other losses in the system to get it to your house, but those are already accounted for in what they charge you. So if you are calculating costs, the car monitor isn't the measure, the wall socket is. Some people get a meter placed on that charger socket, so they can get a true picture of their costs/consumption.

-ERD50

 

[swakyaby]

True there are losses in conversion from AC to DC. Tesla states their conversion takes 11%. But many people seem to forget that electric cars are more efficient in converting stored energy into driving the vehicle. Electric drive vehicles do not consume energy while at rest or coasting, and some of the energy lost when braking is captured and reused through regenerative braking, which captures as much as one-fifth of the energy normally lost during braking.

 

[ERD50]

True there are losses in conversion from AC to DC. Tesla states their conversion takes 11%. But many people seem to forget that electric cars are more efficient in converting stored energy into driving the vehicle. Electric drive vehicles do not consume energy while at rest or coasting, and some of the energy lost when braking is captured and reused through regenerative braking, which captures as much as one-fifth of the energy normally lost during braking.

Whatever "many people seem to forget" is not relevant. Only the facts are.

The effects of regenerative braking, and the efficiency of the battery/motor are already in the numbers that T-Al reported. Charging losses are not. Since T-Al was trying to calculate the cost of his electrical power, he needs to know what is drawn from the socket, not just what was drawn from the battery.

And EVs certainly do consume energy while at rest or coasting. The AC/heat may still be on, lights, battery management, etc. And also look up "vampire" power and EVs.

-ERD50

 

[Bamaman]

The initial cost of the electric/hybrid vehicle will be much higher however. The unknown part of the equation is the life span of the batteries.

If I was going electric or hybrid, I'd be leasing. Let the bank, manufacturer or leasing company take the risk of the lease end value.

 

[TromboneAl]

As I understand it, the in-car monitors are only telling you how many kWh you use from the battery. But re-charging the battery requires that amount of kWh PLUS the losses of getting that power into the battery.

Until I get my 220V charger installed, I can use my kill-a-watt meter. I ran one charge through that, and found that it took 11 kWh. I forget the particulars. Also, the "miles left" indicator (called the guess-o-meter) is not always right.

I should be able to come up with some pretty good from-the-wall numbers. We're going to go on a short drive today, and I'll see how long it takes to charge back up.

 

[NW-Bound]

Not knowing the state of the battery prior to charging, we do not know what the 11 kWh means (the S version has a 24 kWh battery, while the SV and SL has 30 kWh).

I think it is tough for any manufacturer to predict an accurate "miles left" number. That varies a lot with how fast one drives, up or down hill, head or tail wind, heating/cooling on or off, etc...

By the way, I saw that Nissan offers a DIY charging station for $1K. I wonder what electronics is inside one. Apparently, it is more than just a receptacle or plug.

 

[ERD50]

Not knowing the state of the battery prior to charging, we do not know what the 11 kWh means (the S version has a 24 kWh battery, while the SV and SL has 30 kWh).

I think it is tough for any manufacturer to predict an accurate "miles left" number. That varies a lot with how fast one drives, up or down hill, head or tail wind, heating/cooling on or off, etc... .

Right. There is some margin of error even in just stating the battery is "full", let alone predicting how many miles are left. The only accurate way is to monitor all charging kWh over a period of time, and miles driven. If they don't put meters on the chargers in town, that will be an unknown.

But there are lots of reports on the internet, I'm sure you can find several reports from users who monitor their 115V and/or 220V socket draw per mile over enough time to get a good average.

It's like the old days of filling the gas tank right to the top, setingt trip meter to zero, and when near empty, fill again right to the top (on level ground each time). A few cycles of those give you a good idea of mpg. You can even do a partial fill in between, as long as you record it, and fill to the top on the last cycle. But there is very little error in knowing when your tank is "full", so it's easy. Not so easy with battery SOC.

-ERD50

 

[Faraday]

Great topic,.

Perhaps A Tesla C.P.Owned Mdl S would be a game changer to look into, if you can't wait for The Mdl III. : )

From EIA: The growth of clean electricity and the reduction of vehicle emissions turn out to be closely linked. EVs are also, according to the Department of Energy, already a lot cheaper to operate in most places, even with the very low gas prices out there now. As of April 2, the average price of gas in the United States was $2.07, but an "electric eGallon" was $1.09, the agency said.

The prices are also potentially more stable. "I would much rather make you a bet on what the electricity price will be five years from now, than what the gasoline price will be five years from now," said the Union of Concerned Scientists' Reichmuth. "And when you buy a car, that's what you're doing.

Fact: The biggest consumer of oil in the U.S. is the Military, War is Peace, you want to compete with uncle Sam at the pump in the next five years? : (

Honestly: EV's are the most Fun on wheels!

 

[travelover]

Great topic,.

Perhaps A Tesla C.P.Owned Mdl S would be a game changer to look into, if you can't wait for The Mdl III. : )

From EIA: The growth of clean electricity and the reduction of vehicle emissions turn out to be closely linked. EVs are also, according to the Department of Energy, already a lot cheaper to operate in most places, even with the very low gas prices out there now. As of April 2, the average price of gas in the United States was $2.07, but an "electric eGallon" was $1.09, the agency said.

The prices are also potentially more stable. "I would much rather make you a bet on what the electricity price will be five years from now, than what the gasoline price will be five years from now," said the Union of Concerned Scientists' Reichmuth. "And when you buy a car, that's what you're doing.

Fact: The biggest consumer of oil in the U.S. is the Military, War is Peace, you want to compete with uncle Sam at the pump in the next five years? : (

Honestly: EV's are the most Fun on wheels!

Someone is gonna be so happy you showed up.

 

[TromboneAl]

Okay, I did the full experiment.

Yesterday, we were at at full charge (actually 98%). We drove 42.5 miles. Overnight, I charged it up to 100%. The Kill-a-Watt meter showed me the it took 12.14 kWh to charge.

So, that comes to 3.5 miles/kWh.

That should improve a bit with the 220 V charger (although I won't be able to measure it).

 

[ERD50]

Okay, I did the full experiment.

Yesterday, we were at at full charge (actually 98%). We drove 42.5 miles. Overnight, I charged it up to 100%. The Kill-a-Watt meter showed me the it took 12.14 kWh to charge.

So, that comes to 3.5 miles/kWh.

That should improve a bit with the 220 V charger (although I won't be able to measure it).

That's a long way from a "full experiment". As some of us pointed out, the indicator for the SOC (State Of Charge) of the battery is not all that precise or repeatable. You have a single data point, and it would take far more than that to come up with a number that you can have any faith in. A longer term average might be better or worse than that initial number.

edit/add for more clarity: I also would not trust a bunch of single data points. If the SOC is inaccurate, you may just have a bunch of inaccurate numbers. A better way is a s I described earlier - charge to "full", record miles and all kWh in for several consecutive charge cycles. For example, if the SOC was 10% off, by the time you get to 10 cycles, that error is reduced to 1/10th, just 1%. Because you didn't rely on it for each cycle, only the start/end points. Sorry if this comes across as pedantic, but my career was involved in measurement and measurement error, so it's hard to let things like that just sit there!

-ERD50

 

[TromboneAl]

Someone else did the experiments for me:

http://avt.inel.gov/pdf/fsev/SteadyStateLoadCharacterization2015Leaf.pdf

 

[ERD50]

Someone else did the experiments for me:

http://avt.inel.gov/pdf/fsev/SteadyStateLoadCharacterization2015Leaf.pdf

The 120 V charging eff% is pretty low - 62% - 78% through the cycle, and pretty linear?

220V is ~ 81% ~ 91% , and looks to reach high 80's pretty quickly (a good thing).

Gotta use the right denominator, an average ~ 70% loss @ 120V means you need 1.43x the kWh from the socket to end up with 1 kWh in the battery.

Power factors were surprisingly high, very near unity.

But unless you meter the socket, you'd still be trying to use these generalized factors against the car monitors, and the accuracy of those are questionable. If I were buying an EV for the fun and tech side of things, I'd just have to have a meter on that socket! But that's just me (and a bunch of people on the EV forums who report their numbers).

-ERD50

 

[NW-Bound]

The trickle charging is less efficient. There's a baseline usage of 300 watts, so having the charger on for 18 hours means you pay more for a charge.

Also, with Time of Use electricity, our low rate starts at 9 PM. With a trickle, you may need 20 hours of charging, so if you want the car ready at 7 AM, you're going to need to do some charging at 26 and 38 cents per KwH.

7.41c/kWH, wow!

Not knowing about the hardware inside the chargers, I was surprised to learn that there's such a large difference in efficiency between low-power (Level 1) and high-power (Level 2) charging.

If the loss is entirely due to the conversion of power from AC to DC, then perhaps that is because of the inferior design of the Level 1 charger that is meant to be used only as a backup charger (same as a spare tire not being of the same quality as a normal tire to save cost).

Regarding the lower off-peak price of 7.41c/kWh in my area, I forgot to mention that the peak rate is 22.26c/kWh for the summer. In the winter, the peak rate is 10.20c/kWh.

I can also choose a fixed price plan of 8.03c in the winter, and 13.31c in the summer.

 

[ERD50]

Not knowing about the hardware inside the chargers, I was surprised to learn that there's such a large difference in efficiency between low-power (Level 1) and high-power (Level 2) charging.

If the loss is entirely due to the conversion of power from AC to DC, then perhaps that is because of the inferior design of the Level 1 charger that is meant to be used only as a backup charger (same as a spare tire not being of the same quality as a normal tire to save cost). ...

It did seem odd, but I think T-Al's comment on 300 W baseline is the key.

It sounds like there is some fixed wattage just to keep the battery charger systems up and running and monitoring during charging? Those fixed amount of watts would be a larger % of the Level 1 charge.

The table in that pdf shows that the efficiency of Level 2 at its lowest charge rate of 1.41 kW is pretty close to the Level 1 charger at its max charge rate of 1.38 kWh -- 81.5% (L2) versus 78.4% (L1).

(I assume it auto-adjusts to battery conditions, slowing down as it nears completion?)

The lowest wattage loss is at L2 low current, 81.5% of 1.41 kW is 261 watts wasted, and L1 wattage losses are only a little higher (287 and 298 watts). I'm not motivated enough right now, but I think a pretty good estimate could be made of the fixed and variable losses there, and I'd eyeball the baseline ~ 130 Watts (assuming the L2 low current mode would be near 92% eff without the fixed part, that cuts the 260 Watt loss to 130 W), my next step would be to plug that in to the L2 high current rate, to see how it fits, but not now!

-ERD50

 

[NW-Bound]

300W is a lot of "overhead" power to waste, if it is the power that the charger dissipates even if the battery is not taking in any. What do they do? Have a big heater in there? What could it be that uses that much power just idling?

 

[ERD50]

Yes, but my eyeball estimate says it is maybe 130 watts, not 300. There is less than 300 watts of total waste in some of the charger modes, so the fixed waste is only a portion of that. And it may be even less than my 130 watt guestimate.

Still,the power of a 100 watt light bulb is not just a little monitoring going on. Maybe the Leaf forums have more detail?

-ERD50

 

[TromboneAl]

Here's how my usage has gone up. Got the car on 5/18/2016: