2011 Chevrolet Volt: How We Measure Electricity Consumption

This was a very informative post!! I didn't know you could charge the Volt with both the 240v and 120v cords at the same time - that's nifty. Any reason why you can't charge it using an extension cord though? I can't think of why that would affect anything

Thanks, Dan. The second part is likely the controversial part, the way you report energy usage (gas and electric). It seems like you have 2 basic choices for the gas portion:

1. Report average MPG while operating in Charge Sustaining mode. You'd need to report a percentage driven in CS mode so people can normalize the figure to actual fuel use, particularly because not a single person will be used to the idea of computing a MPG over a select portion of a drive.

2. Report actual miles per gallon, where miles represents all miles driven and gallons represents all gallons used. You should still report percentage driven in CS mode though it will be pretty obvious depending on how high or low the number is. That is why I think this number is more intuitive and more reflective of being able to use ~35 miles of battery before burning a drop of gas which is the way most people will use the car.

For electricity you would report kWh to fully charge, and end up with a kWh/100 mile rating as this seems to be the new standard. For a given drive, if you report gas mileage using #2 above, you would naturally report the electricity used, which will most likely be around 13kWh for a full charge.

I also want to point out that in prior blog comments I repeatedly mentioned the number 13kWh when talking about the energy to charge the Volt. I suspect your numbers are about as low as anyone will see. In cold climates, charging cost can spike dramatically, particularly if you use the remote start. It tries to use grid power to precondition the car (HVAC mainly) but I understand ~13A @ 120V just can't keep up and some cold mornings you'll end up with a less-than-100% battery. One dirty little secret of the car is on these cold mornings (<26°F), the engine may run even when you have ample battery reserve. It's a requirement to get battery temperature up as fast as possible.

I know I mentioned the Kill-A-Watt and I am glad you confirmed you are using one. I have the cheapo P4400 and it works great. Hopefully staffers make a habit out of taking the car home and charging it over night, the most common use-case for the Volt.

That Coulomb charger is pretty cool. I heard about them but hadn't looked into it. Apparently they are trying to catalyze a whole sub-economy for charging, if I read between the lines correctly. Sounds like a great incentive to get private industry in on making charging stations more common and publicly accessible. Also don't overlook the OnStar info provided via the website or even the smart phone app(s).

I think "miles driven/gas used" is still an accurate way of presenting fuel economy for the Volt. Whenever gas is put in the car, I would like to see the following recorded: miles driven since last fillup (maybe with electric/charge sustaining mode breakdown if it's easy to access), number of charges since last fillup, kWh of electricity used for said charges. This would give you the overall MPG, the charge sustaining mode MPG, and the approximate cost in electricity usage.

I'm no statistics major, but isn't it about money in versus miles out? Or, what's the cost per mile regardless of how the Volt is moving? It seams you have (or will have) all the data necessary to calculate what it will cost to move the Volt for, say, the first 1K or 2K miles. Correlating this with the rest of your fleet should be easy. Just convert the MPG numbers to cost per mile numbers. Did i miss something or is it really that simple?

The simultaneous 240V and 120V charging capability of the charger only works when two different cars are connected. You can't charge any one car with both at the same time.

Interesting and informative write-up, but, as timtrain35 also asked, can we take it a step further and try to derive how much electricity charging really costs for an average consumer?

Let's say 12.5 kWh is about as much as daily electricity usage of your home AND you do drive off all 10 kWh per day (e.g., 30-mile commute).

If you are conserving energy at home and do not go over your baseline quota, let's say your per kWh tariff is $0.12.

So, if you have to charge your Volt every night before your commute, you will effectively get into "tier-3, 200%+" electricity tariff (e.g., as with PG&E) which will run you almost 4x the baseline price, or $0.40/kWh.

So, now your daily electricity charging-only costs are 12.5kWh*$0.4 or $5/day. If you are like me and fill up with gas once every 10 commute days or so, your "electric tank equivalent" will be $50. I am now paying $50 for a full tank of gas for the same commute.

Am I missing anything here as far as assumptions and calculations?

dkgsx,

The spoiler is that utilities will often bump up your baseline quantity if you tell them you are charging an electric car. I believe PG&E, which you mentioned, is one such utility that will do this.

@timtrain35: Yes, that's where we're headed. But the intermediate step to mpg and kWh/100 is necessary to see how our Volt is doing compared to the rated performance on the window sticker.

dkgsx,
There's a couple of options for you, take a look at this website I was able to find in just 2 minutes (thanks google). You might be able to get rates as low as .05 cents per kwh at off-peak. Check it out and see if it works for your home. I think you have to run a TOU meter for just the EV or Plug-in.

http://www.pge.com/about/environment/pge/electricvehicles/fuelrates/index.shtml

They have a log book for the gas, and they have a log for the power. Its a little hard to figure out precisely how much power you used on a trip without recharging and then combining without much fuel you used... They are doing enough that these figures can be figured out later in their fuel economy reports.

The alarm goes off when you unplug the car? How long does it go off for using precious battery power?

I am surprised to see 12-13kwH required to charge a capacity of 10.x kwh. 20-30% charge loss is rather significant.

hopefully your networks email exchange server isnt down...otherwise your car will be honking its batteries dead when that vandal unplugs it from the charger.

The keycard and web-enabled reporting excites my inner geek.

OMG, I would hate the live in a place that I have to worry about peak and off-peak hours and different rates.

kWh * .06343 + tax = bill

@those who want cost/charge v. kWh .. Cost would be fine but that data can grossly under/overstate the costs for a Volt owner in other areas.

Electricity rates can vary by time of day, with off-peak power costing significantly less. Off-peak is typically during the night when the average Volt owner will be recharging.

Electricity rates also vary wildly across the country, with some people paying over 30 cents/kWh while I, for instance, pay under 7 cents per. Volt owners with domestic solar/wind might not pay anything.

Ideally, Edmunds should continue to cite the charge amounts and additionally publish a spreadsheet or online tool that lets the individual plug in their own electric & gas rates to see how an identically driven Volt (and other future plug-in hybrids & EVs) would fare under their costs.

"I would hate the live in a place that I have to worry about peak and off-peak hours and different rates."

This is the reality with EVs.

The charging is fully programmable, in the car. If you live in a multi-rate area, you can basically program your rate schedule into the car and it will manage itself with respect to charging when it is cheapest. It supports peak and off-peak, as well as a summer/winter schedule. You can also do a more simple time delay charge and say "Have it fully charged by 6am." It'll start whenever, to get it done by 6am. Or you can just have it charge when you plug it in.

The Coulomb may also support fancy multi-rate schedules.

I believe the alarm only goes off when unplugging the cord if you arm it/lock the car while charging.

@lostboyz: Significant indeed. Charging losses are the dirty little secret of plug-in cars, and their makers would rather not talk about it. If they published the usable capacity, wonks like us could compare that figure to the measured amount in a charge to figure it out. But all of the home 240V chargers I've seen lack any sort of per-charge meter, so the typical electric car owner may never see it even if they did know the usable capacity. That's one of several reasons why we purchased this more expensive commercial and fleet-oriented charger instead.

Engineers from various automakers have flat out admitted to me that they would rather not announce a usable capacity because they fear it lets their competition learn something about how they manage their battery's state-of-charge and the efficiency of their charging system. In these early days of the electric car these are still considered trade secrets, and the difference between the usable capacity and the rated capacity is at the heart of battery technology advancement.

But to us, the usable capacity is the size of the electric "gas tank" that consumers will fill. Who doesn't know or want to know the size of their gas-powered car's fuel tank? You'd be pissed, and rightly so, if the carmaker refused to tell you and failed to list the gas tank capacity in the owner's manual. Why should plug-in cars be any different?

Finally, the all-important federal electric car tax credit is based on RATED capacity, because government doesn't know what it's doing. The value of this tax credit ramps up to as much as $7,500 as rated battery capacity increases. Care to guess the minimum number of kWh of rated capacity necessary to earn the maximum $7,500 tax credit?

That's right, 16 kWh -- the precise rated capacity of our Chevrolet Volt. The Nissan Leaf, a true electric car through-and-through with no gasoline engine, 24 kWh of rated capacity and about double the electric range, earns the same $7,500 credit as the Volt.

I should add that ONE element of our vast government understands and recognizes charging losses: the EPA window sticker for electric cars measures electricity consumption at the wall, like we do, to figure the electricity consumption of EVs and plug-in hybrids. Of course they go and muck it up by making a silly and useless conversion to MPGe that ultimately results in a number with little relevance to consumers, but that's yet another topic for another day.

Great explanation, first time I've read enough to put pencil to paper for my situation. In NW Fla, Gulf Power charges about 6 cents per kWh including all the bs taxes and surcharges. If I used 12 kWh every day to replenish the Volt, it would cost me less than $20 month for electricity and if GM's range info on a full charge is accurate, I'd only get into the gas engine on an extended trip, which os very infrequent in my case. Compared to the $80 month I spend now on my Focus SVT for 3 tanks of premium each month, I'd come out $60 ahead. Obviously, not enough to make a financial argument for the Volt but helps me put into perspective the potential savings. Sure with this thing cost 25k!

"Finally, the all-important federal electric car tax credit is based on RATED capacity, because government doesn't know what it's doing."

Well the tax credit was supposed to bring down battery costs over time, so the only thing the government cares about is OEM's buying as much battery capacity as possible, rest is car makers choice.

@wjtinatl: Are you sure about the $0.06? That's far lower than the 11.8-cent Florida state average listed on the DOE website. http://bit.ly/9ZhVvL

Try this before you get too excited: Divide your total monthly bill buy the number of kilowatt-hours you consumed that month. That's a better ballpark figure to work with, but even that could be misleading if your utility uses a tiered rate structure like mine does.

For me, the California state average is listed as 14.6-cents. My average bill, as roughed-out with the above method, works out to 22 cents including all taxes and fees. But reality is worse than that. My rates are tiered through 5 steps. My rate starts at 12 cents, the increases to 16, 21, 27 and 31 as consumption goes up. My lifeline rate is tiny, I have no pool, no second fridge in the garage, gas heat, gas water heater and 2,000 square feet. Nevertheless, in winter with no AC I'm deep into tier 4. In summer with AC on at times I'm firmly into tier 5.

Electric cars have to be considered an optional lifestyle choice, so you have to figure their electricity cost as "last in" at the highest tiered rate your household is using. Furthermore, the extra e-car usage will probably push you up into the next highest tier. For me, the Volt or Leaf are charging at 27 or 31 cents per kWh, mostly 31 because of this last factor.

But my utility bill starts at 12 cents and the state average is 14.6. Clearly, this is a complex issue, and I haven't even started talking about off-peak and separate-meter rate structures that I could opt in to. This is a massive topic.

"Step One is measuring gasoline consumption at the pump. That's easy. We already know how to do that."
Donna would think otherwise...

@mario87: Use, but basing the credit on usable capacity instead would reward the development of efficient charging systems and batteries, not merely big ones.

@actualsize

I guess so, but in the end doesn't the auto companies have a incentive to make the car as efficient and durable as possible over time, they are after all competing with other automaker.

Also I don't know if you have stated this before but what is your electric utility? Off peak would be the key, I don't think many people understand how much excess electricity is produced/available at off peak.

@actualsize

Link provided on the rates include surcharges, and taxed calculated out per kWh? If so its about 3 cents higher, if not well its almost double what anyone i know pays.

Im at .06343 KwH, with taxes, charges, and fees it hits .09199. I wish I had gas though, when winter hits I have all ele. Heat pumps do a fairly good job as saving $$$ over strip heating. But I just got a $170 light bill. :o

Anyways, by rough calc this car would be stupied cheap. Sadly my commute is 50 miles a day in some rouch traffic. So I would hit the pumps and would take away from some of the savings.

@mario87

My personal utility at home is SCE (Southern California Edison). Yes, I can sign up for an off-peak program with an advanced electric meter, but so far I have not. The electric rates are cheaper at night when I would charge an electric car, it's true, but the very same plan pushes my daytime summer rate to 55 cents per kilowatt, right when I'm using AC.

SCE helped me do an electric car analysis and it showed my annual electricity cost would be virtually THE SAME using the standard program versus the off-peak program. If I lived at the beach and used no AC in summer, I'd be all set and would save big. But I live inland where it gets hot in summer. No free lunch for me. Since I am not the only driver of this car and only charge at home infrequently, I'm sticking with my current 5-tier fixed rate plan.

Moral: study the off-peak rate programs carefully. In my case, off-peak went down, but on-peak went up, especially in summer.

These are all fantastic issues we can finally explore, in earnest, the logistics of a car charger lifestyle. The issue of the off-peak charging electric plan impacting day time rates is absolutely an important element to this. Prospective customers should definitely explore this for their region to see how car charging will impact their bill overall (not just for the car charging, itself).

I believe it is important, at this point, to track *both* kWh+gal and electric+gas costs as we forge ahead on this longterm test. Different people will be concerned about different pieces of information, so there is no need to adapt only one way to express energy or fuel consumption for this project. Both tiers of data are important for the purpose of quantifying energy costs that can be related to people in different regions across the US and also to quantify the energy costs that Edmunds staff actually experienced in their use of the product. If possible, it may also be useful if the staff logs instances of day charging vs. night charging. That way, you can later give a qualifier at a later date that your electric costs emerged from mixed charging instances of about x% night charging.

"That's right, 16 kWh -- the precise rated capacity of our Chevrolet Volt. The Nissan Leaf, a true electric car through-and-through with no gasoline engine, 24 kWh of rated capacity and about double the electric range, earns the same $7,500 credit as the Volt."

Getting by on the minimum is as American as baseball, apple pie, and bank bail outs.

this is the equivalent of needing to pump 24 gallons of gas to fill a 20 gallon tank, charging from an 120V system would have even more losses. I would be curious to see if there have been any iEEE papers into BEV average charge losses. Going to investigate.

actualsize:

Thanks for that explanation about the off-peak charges and your rates changing. The utility companies will make or break electric cars, when all is said and done.

If the companies try to exploit this, electric cars and plug-in hybrids will fail. The only way to avoid this, if a person wants an electric car or plug-in hybrid, would be to have solar on their residence. Obviously not everyone can afford to do that.

However, I will disagree with you about the rebates. Yes the Leaf has more rated capacity, and range. If the government were simply trying to help the Volt, they would have exempted the Leaf from the rebate, and all other foreign manufacturers. Remember, GM actually studied how many miles the average driver drives daily, and came up with 37 miles. That is where the initial 40 mile range came from. If the results of the study had been more, the electric mile range would have grown accordingly along with battery size.

For those complaining about EVs not being 100% efficient at charging, I hope you realize that pumping gas isn't 100% efficient either. Fuel is used at multiple stages to transport gasoline, more fuel is used to pump the oil, more fuel is used to refine it, fuel in the form of electricity is needed to run the gas station pumps, and so on. The inefficiencies are simply buried in the price so you don't notice.

Did you know you get 44.x gallons of refined oil product (gas, diesel, asphalt etc) from a 42 gallon barrel of oil? That should count as a counterweight against the inneffiencencies of its transport....like 10000 miles from saudi arabia.

@fushigi: true enough, but the same can be said for making the electricity. What I'm talking about here is a specific difference on the ownership side between gas and electric cars. You pay for 10 gallon, you get 10 gallons. You pay for 12 kWh, you get 10 kWh. It's a specific difference that pertains to ownership -- a hidden cost.

The cost of the stuff you're talking about is baked into the fuel price for all to see.