# What Would an Electric Car Do to Your Electric Bill?

Supposing I had one of those nifty electric cars… If I plugged it in and charged it up, say, twice a week, would my electric bill go through the roof?

A gallon of gasoline has as much energy as about 35 killowat hours of electricity. Here in Massachusetts, I pay about \$0.13 per KWH, so that would be the equivalent of \$4.55 a gallon. If you live where there is an abundance of hydroelectric power, you probably pay less. If you charge your car only at night, you may get a break on off-peak pricing, as well.

Electric cars are more efficient (regenerative braking?), so there’s that factor, too. All-in-all, it will probably cost at least as much as a regular car. Instead of paying \$20 per week for gasoline, expect your electric bill to go up by a similar amount.

\$.28kwatt hour in California. ack. More if you use more.

A gallon of gasoline has about 47.3 MJ/kg, on a higher heating value basis. A gallon of gasoline has a specific gravity of about 0.728 at 60 F, thus it weighs about (0.72862.37 lbm/ft[sup]3[/sup]) 45.405 lbm/ft[sup]3[/sup]. Since a US gallon is 7.48 ft[sup]3[/sup], thus gasoline weighs about 6.06 lbm, or 2.75 kg. Thus, one gallon of gasoline has about 130.22 MJ of energy. This can also be expressed in kWhr as 36.17 kW*hr.

However…the car uses the gasoline with an HHV efficiency of between 20 to 30 percent, varying greatly. Let’s say 30 percent. Thus, only about 10.9 kW*hr of usable energy is available.

Now, IIRC, and electric car has losses due to it’s motor, power converters, charging circuit, etc that give the efficiency of using the electricity supplied to the car of somewhere between 80 and 90 percent. Let’s say 90 percent. Thus, every kWhr of electricty you pay for results in a usable 0.9 kWhr.

At a US average price of, oh, say \$0.11/kWhr, each usable kWhr costs (0.11/.9) = 12.2 cents for the electric car. While at a gasoline cost of, oh, say \$1.30 a gallon, the gasoline car costs about 130/10.9 = 11.9 cents per usable kW*hr.

So…pretty close overall using these assumptions. Feel free to insert your own into the process to come up with your own numbers.

Anthracite, I never thought I’d question you on a point of engineering, but did you really mean to say that electric cars are 80%-90% efficient? Very few devices of any sort are that efficient, and I would have guessed the efficieny to be more like 10%-20%, what with the charging, discharging, and engine inefficiencies.

You picked a bad week to make comparisons.
Try to decide if the public or the power companies will win with Dubya in the White House. Last I noticed, he pulled the restraints off that the Dems had in place. Now electricity is due for a windfall doubling.

Either you have to restate your problem in the past, with historical dollar values, or wait two years for the Congess to switch Democratic again.

In the mean time, there is no ceiling to electricity prices.

Other things to consider:

If you were to get an electric car, you should check with your electric utility to see if they offer a time-of-use rate. Many will offer power much more cheaply at times when overall demand is low (overnight, weekends.) However, some utilities have such god-awful long definitions of when “on-peak” is it wouldn’t be practical for you to use it.

Consider photovoltaic (solar) panels for recharging the batteries. I wouldn’t plan on depending upon them 100% of the time, but they could supply a good bit of the charge. They will have a relatively high first cost, but this could be offset by tax credits, depending upon where you live.

Check out the incentives in your state here:

http://www.dcs.ncsu.edu/solar/dsire/financial.html

Well, I have no online cite, but I do know that motors of the same type used in electric cars do range from 85-95% efficiency. However, I do admit that my recollection of the overall efficiency of the charging circuit is hazy now. I tried to find my reference, and failed.

Thus, I withdraw my ill-informed claim of 80-90% efficiency. If someone has a better value, they can put it into the work I did and find a better answer, in cents kW*hr. I do think my values for the IC engine are pretty correct though.

Most all large Utilities are publicly traded companies. Check their profits in a year, then see if electricity is really too high or not.

Anthracite: The motor is only one part of the equation. You also have driveline losses, Losses due to poor battery efficiency (especially as they age), losses in the charging circuitry, etc. Then there are the other losses that all cars have (rolling friction, aerodynamic drag, etc). But because electric cars are much heavier than the equivalent gasoline powered car, these losses will be higher. A battery’s efficiency in a car has to include the cost to haul its own weight around.

You’ve got an electric car with maybe 2000 lbs of batteries in it. After driving one for an hour, see if you can put your hand on the batteries. They get very hot. Heating 2000 lbs of material like that is VERY expensive in terms of energy.

Then there are the losses in creating the energy, transmission line losses getting it to the charging station, etc. But they’re another issue, because the individual isn’t billed for them.

And if you really think power companies will make a killing, put your money where your mouth is and invest in them

Arjuna34

We’re not considering those losses. I am a “World Expert” (or at least my title says so) in coal and other power plants. I know all about the losses of power generation, transmission, and distribution. I could post a 77-page report I wrote on them, if I cared to. The comparison here was w.r.t. end-user cost, not overall efficiency.

I also know about the other losses of the electric vehicle. I helped build and test and electric car in grad school, and did most of the efficiency analysis on it.

Where you are correct is that my posts here have not been clear or good on the issue of the electric car power conversion efficiency. I guess I’m just not thinking well today - I just officially ended my relationship with my SO of 8 years, and am now truly living in the House of Pain. Hell, earlier today I would have taken a whole bottle of sleeping pills with the whole bottle of wine I drank, if not for friends online who helped me this afternoon. Thus, all things considered, you should be impressed I got the IC engine numbers right.

And on that note, perhaps I should leave the Board forever. I don’t know. Maybe, maybe not. Things are pretty black right now, and kinda sad.

Time to try and redeem myself here first tho. Oh yes…what were we talking about? Well, I searched for a while, and did discover this link:

AC Propulsion Questions that Should be Frequently Asked

Which says:

I found numerous other references that threw out “95%” or higher motor efficiencies, but with no real backing.

This same site above claims that:

If we take this sample-size of one site as gospel, and take the worst-case figure of 0.250 kW*hr per mile at 70 mph, and compare it to a typical IC engine car which gets about 25 mpg at 70 mph, let’s see the cost per mile at 70 mph:

IC engine car - (130 cents/gallon) / (25 miles/gallon) = 5.2 cents/mile

Electric car - ((0.25 kWhr / mile) / .8 charging eff) = 0.313 kWhr/mile that must be charged.

Thus, at our rate of 11 cents / kWhr, we have 11.313, or 3.44 cents/mile.

Hmm…still doesn’t seem quite right. Ah! I see. There is also a discharge efficiency to take into account, given in my searches as being “about 80%”. OK, now we have:

3.44 cents/mile / 0.8 = 4.3 cents/mile.

OK…in terms of end user cost only, what else am I missing here?

It need not cost you anything to recharge your car. In California there are hundreds of free charging stations, typically located at shopping malls. Or there were before the crisis. I haven’t heard about them since then so I assume they’re still there.

Well the best I can offer in terms of the electric car is the following.

http://solstice.crest.org/efficiency/ev-list-archive/9711/msg00009.html

This purely empirical evidence seems to indicate 80% efficiency is reasonable. While this is not totally authoritative it’s the best I can find, has any one got full independent case study information?

I’ve often wondered how efficient an electric car would be in cold climates.

For comparison, look at a car with an internal combustion engine. The heater setup is very efficient; you circulate the engine’s coolant through a small radiator (heater core) and circulate air through it with an electric fan. The heat itself is practically free (i.e. it would probably be wasted if you weren’t using it), so basically all you’re paying for is two things:

1. Power to run the electric fan
2. Power to circulate water through the heater core

Given that the water pump has to circulate coolant through your engine anyway, # 2 is probably insignificant, so I would guess the only real expense is #1 (which probably isn’t all that much).

Flash forward to an electric vehicle. How does its heater work? An electric heating element, I would guess. How much I^2 * R power would an electric heater use when it’s 10 ºF outside? I don’t know. But I would guess it’s quite a bit. Translation: I would guess the efficiency of an electric car really sucks in cold climates. (Not to mention battery capacity suffers at lower temperatures.)

Getting back to the weight of the vehicle - If you built an IC car with the same level of amenities as a typical electric car, it would get much more than 25 mpg. The proper comparison with an average electric car would be more towards an ‘economy’ IC car, which might get more like 35-50 mpg. Remember, an electric car has to haul around thousands of pounds of dead weight in batteries, and pay the price for that.

Anthracite: Sorry about your breakup. And I certainly didn’t intend to disparage your engineering knowledge - you’re one of the bright lights around here. I just thought your message was incomplete.

Once you have an electric car in your hands, the cost per mile of the actual electricity isn’t bad. But to be realistic you have to compare the cost of the entire system from purchase to disposal of the car at the end, plus maintenance. And this is where electric cars really have a hard time competing. They are mondo expensive to build, those thousands of pounds of batteries have a finite life, and therefore the maintenance cost per mile is prohibitive.

It used to be that the big drawbacks of electric cars were acceleration and range. The latest cars are actually pretty good in that regard. Now the big problems are cost, lifespan, disposal, etc. That’s why the main electric cars that are available now are not available for purchase - you can only lease them.

Anthracite says;

That pretty much agrees with an article I read a couple of years ago (before deregulation), 3-4 cents/mile for a Civic size car.
Better batteries (or fuel cells?) will come when the demand is there.
Peace,
mangeorge