## Chevy Volt Energy Usage – Charging on 240v vs 110v

One of the questions circulating around about the Chevy Volt and any other electric car out there is how much more efficient it is to charge an electric vehicle on 240v (Level 2 Station Charging Station) vs. a 110v (Level 1 Charging Station). For those wondering why it would make a difference – it is the same reason that long distance transmission lines from power plants are run at tens or hundreds of thousands of volts vs. your regular household outlet at 110 volts – namely that less energy is lost to the resistance in the wire.

Because I have a ChargePoint Network Installed Charger at home and Have used a couple Public ChargePoint Network Stations, I’ve been able to see that at home on a 240 volt circuit, it takes roughly 11.9 KwH to Fully charge my Volt’s depleted battery. (the weather here has been pretty consistent at around 50-60 F, so chances are – no extra energy was used to heat or cool the battery)

Compare this to my 110v charging experience in the public, and you’ll see that the total power usage was 13.5 Kwh. Granted, I only have one data point here, and certainly there is a possibility for measurement error / slight variations to the Volt’s actual charge depletion when it was plugged in (it tries to maintain 30% state of charge, but it will vary) – But the 13% difference is significant enough to state that there are certainly charging efficiencies to be gained by stepping up to higher voltage.

If you are interested in my Chevy Volt charge data, it is available here.

Is the extra efficiency in having a 240v charger worth the cost difference? Probably not. If you are paying say 10 cent per Kwh, you would basically save 1 cent per KwH by having a 240v charger vs a 110v charger.

If you look at my entire charge history in the excel sheet, You’ll notice that I’ve used 544 Kwh since buying the Volt (netting roughly 1760 EV Miles). To offset the cost of installing a charger (lets call it $1,000 though we all know it can be much more) You would need to charge for 100,000 KwH or by my math, drive 330,000 EV Miles.

Of course the real benefit is the ability with 240v to charge quickly and displace more gasoline usage – which I’ve certainly done a lot of.

Read more about my Level 2 Charging Station Installation here for more background on what it takes to install a Level 2 Charger at home

“You’ll notice that I’ve used 544 Kwh since buying the Volt (netting roughly 1760 EV Miles)”

I did. It looks like your energy efficiency while driving in EV mode has gotten much better since you posted your OnStar monthly report in early February. I’m curious what your subsequent monthly reports look like. In particular, I want to know how closely the OnStar “electricity consumed” field matches your own charging data.

I was down to a monthly average of 28 kWh / 100 miles on my last report 3 weeks ago. You must be close to that. Enquiring minds want to know!

O

So basically at 3 bucks a gallon that would be like 120 miles a gallon. That’s incredible. I can’t wait for my electric 4×4!

I confused the date on your OnStar posting. It was January 21. Maybe you can post an update when the next report gets sent out in another couple of weeks.

Hey Jeff,

I will put the caveat in that I’ve pulled down a little more than 544KwH on the odd chance I was charging in a non-chargepoint station. I can probably think of 5-6 cases where I took a full charge at a friend’s house etc. so I would add 60-80 KwH to that total to be totally accurate.

For the Onstar report I was at

Electric Consumption: 35 kW-hr/100 miles

Compare this to my data which is 544 KwH + 60-80 KwH untracked = 600/1760 or .34 Kw per mile or 34 kw per 100 miles. It might true up exactly on the dot if I guessed my “untracked usage” low.

So the numbers are actually truing up pretty well!

Just to note, my electric efficiency is probably “lower” because I drive pretty hard in the city (Fast accelerations, but regenerative braking mostly since I know I won’t use any gas that day) And most of my mileage is local driving.

I know Onstar is working on efficiency benchmarks in MyVolt, so hopefully we’ll be able to compare stats soon!

Patrick

Patrick, good chatting with you last night in the focus group. Love the website. Adding it to my feed. C

Interesting results. Faster charge rates means more heat loss. Using Cherolet’s currents and time you get at 120V “recharge the car fully in 6 hours at 12 amps or 8 hours at 8 amps.” and at 240V “running at 16 amps can recharge the Volt in 3 hours” Some simple calculations:

1120V charge

120*8= .960KW, .96 * 8 = 7.68 KW-Hr 8 Hours at 8 amps

120×12=1.44KW, 1.44 x 6 = 8.6KW-hr 6 hours at 12 amps

240v charge

240*16=3.84KW, 3.84 x 3 = 11.52 KW-Hr 3 hours at 240.

You measured 13.5KW-HR at 240 volts ~ right but 2KW-hr high. I suspect the 120V measurement did not account for another load.

Fatser charging means more heat means less efficiency.

Bruce, I’m not sure where you got those numbers from, but 6 hours for a full charge on 120V/12A is way off. It’s ~10 hours for a full charge on 12A, and I believe it’s ~16 hours for a full charge on 8A.

Using the rest of your math:

120*8= .960KW, .96 * 16 = 15.36 KW-Hr 16 Hours at 8 amps

120×12=1.44KW, 1.44 x 10 = 14.40 KW-hr 10 hours at 12 amps

Those numbers square up more readily with the rest of the analysis in this thread, though I think there’s still a little bit of fudging going on. Real world analysis (with Kill-A-Watt style meters) shows the Volt pulling in a little over 13 KWh with the 120V charger.

I believe that 240v is more efficient to begin with as its going over a broader path, 3 phases. The heat is not a factor as the charger would be designed to handle that input power. Based on my basic electrical training and experience in datacenter power, i believe your claim is false in this example.

The 240 volts at your home is not 3 phase.

Now I’m confused. Bruce shows 11.52 KwH to charge at 240V versus 7.68 to 8.6 on 120V. The author of the original post indicates that he or she used less total power using 240V. Can anyone else weigh in on this?

Tailfins,

The author used less energy while charging at 240 volts than at 120 volts because of the resistive energy losses that occur at higher currents. Going by the author’s data (13.5 kWh used at 120 volts and 11.9 kWh at 240 volts) and assuming he was charging a fully depleted battery, there was a loss of 3.2 kWh when charging at 120 volts and a loss of 1.6 kWh when charging at 240 volts. This is fairly consistent with Joule’s law of resistive electrical losses, which states that losses are proportional to the square of the current passing through the wire. Of course, there is also the issue of the resistance of the particular wires being used and its gauge. Because resistance losses are dependent on current and not voltage, the doubling of voltage effectively doubles the supplied energy while exhibiting the same amount of resistive loss as charging at 120 volts (this if he is charging with 12 amps at 240 volts, which is what the data suggest if he gets a full charge in 4 hours). So, now that the energy losses are the same, the one delivering the most amount of energy (the 240 volt charger) will exhibit only half the overall losses in electricity because it is charging twice as fast. It is crucial to remember that the electrical losses are usually giver per hour, so charging at This is why it ends up being more efficient to charge at a higher voltage. Same reasoning for why electricity at extremely high voltages and at very low currents are used to deliver electricity across the states.

whoops, I forgot to finish my thought near the end there. I meant to say that because resistive losses are measured in watt*hours, the voltage that requires the least amount of time will end up being the most efficient.

I clicked on your link to view your Chevy Volt charge data, where did you get this data? Is this from the ChargePoint site or from your Volt? I want to get the same exact data for my Volt.

Please let me know. Thanks.

This is from the Chargepoint site, if you have a Chargepass or a home Coulumb CT-500 type station with networked access.

Patrick

I am interested in purchasing a volt can someone tell me at 220v input on the charger, what is the draw on the primary side of the transformer. I would like to do some calculating on usage to charge 0-1/4 0-1/2 0-3/4 0-full thanks in advance. Also foes anyone know if they make a charging unit that us solar charged.

I have a 2011 Nissan Leaf and the battery state of charge can vary due to ambient temperature. That may explain different SOC levels post either 120 v or 240 v charging. But, in my view, the issue of electrons is too specific since the science and variables can be detailed and difficult to explain. All that is needed to know in an “executive summary” type of analysis, is that like any machine in motion, tire/road resistance, wind, speed of the vehicle, weight, elevation changes and density of air, will affect miles per kW/hr. These cars do best in city slow, stop and go or moderate speeds conditions. No doubt, a Level 2 charger at home allows for faster “recycling” of the car as in return from work, park for two hours, then need to drive again. No worries as to “return of investment” as these calculation serve best to drive owners crazy. The main objective is to use the least amount of gasoline as possible to reduce car pollution.