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Concentration of CO2 in the Atmosphere

Electric Cars: Are They Better for Your Pocket and the Climate Right NOW?

Charging (Shutterstock image)

Jayd Alvarez

I read a blog post from Connecticut Fund for the Environment President Curt Johnson, and he reaffirmed what I already expected: my next car will likely be an all-electric vehicle (EV). I currently drive a Toyota Prius hybrid, because in 2013, the price to purchase and to operate an EV did not work out. I chose the Prius hybrid instead, which has very reliably achieved 50 mpg over the last six years.

As an engineer who admittedly knows nothing about cars, I feel information out there on EVs is either slightly biased (i.e., published by EV manufacturers) or not supported enough by the math to convince me. So, I set out to create a blog post that was unbiased and transparent. I liked one from Tom Murphy (https://dothemath.ucsd.edu/2011/08/mpg-for-electric-cars/), an associate professor of physics at the University of California, San Diego. Here, I’m adapting it to be a bit more user-friendly and applicable to your current or local situation.

I just wanted to know two simple things (and admit to ignoring a long list of other factors that influence the type of car most people will choose to drive).

Number 1: At what gas price is an EV cheaper to drive per mile?

Number 2: While EV tailpipe emissions are zero, what about the emissions from the power plant supplying the electricity for my car? I know my next car will be electric, but is the local grid clean enough so that it’s better for the environment when I switch?

When I began writing this article, I had no idea what the answers would be.

1. What Costs More Per Mile to Drive? Gas or Electric?

The math is straightforward. Let’s assume the car you drive achieves 50 mpg and you drive it 10,000 miles per year.

10,000 miles/50 miles per gallon (mpg) = 200 gallons of gas. Multiply total gallons by the local gas price (let’s say, $2.50 here in CT) and your annual cost to drive is $500. (Yes, this completely ignores the purchase and maintenance costs. The calculator at https://www.befrugal.com/tools/electric-car-calculator/does a better job of that. More information can be found at https://www.cars.com/articles/should-i-buy-an-electric-car-or-plug-in-hybrid-1420757712263/.)

Electric cars aren’t rated in mpg, and I don’t like the MPGe ratings I have seen, and like Mr. Murphy, I prefer the kWh/100-mile approach.

Quite a few EVs are reported to get 100 miles of range for about 27kWh of electricity, and we’ll round that up to 30kWh to account for ~10% charge inefficiency. For comparison, 30kWh is the same amount of electricity needed to power thirty 100-Watt incandescent light bulbs for 10 hours (not that you still have any of those).  For the sake of this article, we’ll assume the average driver will get that range from their EV for that charge.

10,000 miles/100 miles per 30 kWh = 3,000 kWh. Multiply by local electricity price (let’s say, $0.15 per kilowatt hour) and your annual cost to drive an EV is $450 ($50 less per year than my Prius).

So, depending on your current car’s mpg, local gas and electricity prices, the math for an EV could work out for you. The table below, based on your current mpg from the far-left column and your average electric rate in the top row, shows you the highest gas price you should pay before a typical EV will save you money. For example, in CT, once gas went above $2.25/gallon, I was spending more on gas in my 50 mpg hybrid than if I drove an EV and paid $0.15/kWh to charge it. For my CT colleagues driving a newer model Prius and getting 70 mpg, an EV won’t save them money until gas goes above $3.15/gallon.  With current average gas prices at about $2.50, most of us will save money by switching, so I highlighted in green all the scenarios where if you are paying $2.50/gallon, an EV will save you money, and in red where it won’t.

$0.08/kWh $0.10/kWh $0.12/kWh $0.15/kWh $0.18/kWh $0.20/kWh
15 mpg $0.36/gallon $0.45/gallon $0.54/gallon $0.68/gallon $0.81/gallon $0.90/gallon
20 mpg $0.48/gallon $0.60/gallon $0.72/gallon $0.90/gallon $1.08/gallon $1.20/gallon
30 mpg $0.72/gallon $0.90/gallon $1.08/gallon $1.35/gallon $1.62/gallon $1.80/gallon
40 mpg $0.96/gallon $1.20/gallon $1.44/gallon $1.80/gallon $2.16/gallon $2.40/gallon
50 mpg $1.20/gallon $1.50/gallon $1.80/gallon $2.25/gallon $2.70/gallon $3.00/gallon
60 mpg $1.44/gallon $1.80/gallon $2.16/gallon $2.70/gallon $3.24/gallon $3.60/gallon
70 mpg $1.68/gallon $2.10/gallon $2.52/gallon $3.15/gallon $3.78/gallon $4.20/gallon

If you want the table in an equation form so you can further tailor it to your situation:

Max Gas Price per Gallon = ([$/kWh] x [mpg] x [kWh to drive 100 miles])/100

For Example: Max Gas Price = $2.25 = ([$0.15/kWh] x [50 mpg] x [30 kWh to drive 100 miles])/100

How can you calculate the average price for electricity ($/kWh) from your local utility?

The simplest way is to take your last electric bill and subtract out the monthly service charge. (Mine is called “Distribution Basic Service” and it is $12.84 per month, irrespective of how much electricity I buy.) Divide what is left by the kWh you bought that month (155 kWh in my example). This is an approximation and can change month to month. If you have different rates for on- and off-peak, you could just sum the off-peak charges, assuming you will charge your car at night. My bill is below and is roughly $0.148 per kWh, off-peak. While I do have solar panels, I use all that electricity on my household electricity, and don’t have enough left over to charge a car for “free” overnight. I estimate here in CT, I’d need about 2.5kW of solar, about 10 classic rooftop PV panels, to make enough electricity (3,000 kWh/yr.) to charge an EV and get 10,000 miles per year.

2. Is My Local Electric Grid Clean Enough?

For me personally, here in CT, it costs me less to charge and drive an electric car than to buy gas for my 50-mpg hybrid. Also, it seems like I might be at the right price point for buying an EV, if local rebates and tax credits reduce the purchase price to within that of a gas hybrid, as indicated by Mr. Johnson.

But, is driving an EV really saving the planet, if I shift my tailpipe emissions to a local power plant? Luckily, according to the EPA, in my region and most others, the answer is YES! The average pounds of CO2 produced per gallon of gas burned is 20 (I did not do the math for diesel engines and bio-diesels). So, again, assuming the same 10,000 miles per year driven in the examples above, the second column in the table shows how many pounds of carbon dioxide (CO2) are produced annually by the gas engines (lbs. of CO2 is a common metric for greenhouse gas emissions, even though there are other greenhouse gases, such as sulfur dioxide and nitrogen oxide).

For a hybrid getting 70 mpg, 2,857 lbs. of CO2 are produced annually to drive 10,000 miles. This goes up to 13,333 lbs. for a truck or SUV getting just 15 mpg.

For comparison, in the table below, I report average emissions for EVs travelling the same 10,000 miles, for a few eGrid regions. I show one state in each region for context and sorted them from lowest to highest, from left to right, with the national average in the middle. I used green to show where gas engines, even hybrids, are emitting more CO2 than the average emissions from power plants in that region providing the electricity to charge an EV to drive the same distance.

In CT, my hybrid is producing 4,000 lbs. of CO2 to go 10,000 miles, whereas the average emissions to generate and distribute the electricity an EV needs (in CT) is only 1,520 lbs. of CO2. (Since some of these regions are really large, if you want to get state-specific values as I did, go to Table 3 of this report and multiply the CO2 numbers in the second column (which are reported as pounds per thousand kWh by 3.05 which accounts for a line loss of 5%).

Even the regions with the highest carbon emission rates for electricity generation (Long Island, Wisconsin) produce less CO2 to charge your EV as compared to non-hybrid gas engines.

Note: The CO2 emissions from eGrid regions represent averages – so the actual value could be higher or lower, depending on the source of the electricity (e.g., gas, coal, wind, solar) at the time you are charging your car.

Lbs of CO2

Lowest

(Upstate NY)

CAMX

(CA)

NEWE

(MA)

Nat’l Avg

SRSO

(GA)

NYLI

(Long Island)

Highest

(Wisconsin)

Gas

EV

EV

EV

EV

EV

EV

EV

15 mpg

13,333

924

1,651

1,750

3,129

3,415

3,694

5,229

20 mpg

10,000

924

1,651

1,750

3,129

3,415

3,694

5,229

30 mpg

6,666

924

1,651

1,750

3,129

3,415

3,694

5,229

40 mpg

5,000

924

1,651

1,750

3,129

3,415

3,694

5,229

50 mpg

4,000

924

1,651

1,750

3,129

3,415

3,694

5,229

60 mpg

3,333

924

1,651

1,750

3,129

3,415

3,694

5,229

70 mpg

2,857

924

1,651

1,750

3,129

3,415

3,694

5,229

While I didn’t touch on issues with batteries, driving range, lack of EV chargers, a car’s ”embodied” carbon (emissions associated with everything from manufacture to disposal), and a whole list of other related topics, I sincerely hope that the math has shed some light on this subject for you.

If you are ready to go shopping for an EV, check out https://www.energy.gov/eere/electricvehicles/electric-vehicles-tax-credits-and-other-incentives for the federal tax credits and other local incentives that may be available. But don’t wait too long. The Federal Tax Credit phases out once the manufacturer sells 200,000 EVs, and Tesla and GM have already reached that milestone.

Jayd Alvarez is a Marketing Coordinator for Steven Winter Associates, Inc.

 

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