Friday 17 November 2017

Comparing Electric, Hybrid, and Gas-powered Vehicles

Posted by at 11:45 AM

As more electric vehicles are becoming available on the market it is important to do an analysis before a purchase. Which is more efficient? Which creates more CO2? Which will have a lower cost in fuel?

It is easy to compare a regular gas-powered car's efficiency against another gas-powered car. To do so, you can simply check how many miles per gallon it gets. But when you're comparing against an electric vehicle it becomes a little more complicated.
To compare fuels with each other we need to convert them to the same measurement; BTUs.

1 Gallon of Gasoline = 120,476 BTUs
1 Kilowatthour = 3,412 BTUs

An average car that gets approximately 30 miles to the gallon uses 4,016 BTUs per mile, which is the equivalent of 1,177 watts per mile.

A higher performing hybrid gas vehicle that gets approximately 50 miles to the gallon (such as a Prius) uses 2,410 BTUs per mile, which is the equivalent of 706 watts per mile.

Bob has reported that his all-electric vehicle, the 2016 Nissan Leaf, requires 244 watts per mile, or 833 BTUs, which is equivalent of 145 miles to the gallon.

Jim's all-electric vehicle, the Tesla Model S requires 320 watts per mile, or 1,092 BTUs per mile, which would be equivalent to 110 miles to the gallon.

In terms of efficiency, the electric vehicles win. Let's translate this into CO2 production to see the carbon footprint.
Burning a gallon of gasoline produces 19.36 pounds of CO2. The electric grid in Wisconsin is generated mostly from coal and calculating the greenhouse gas emissions is dependant on the specific car and the grid it is coming from. The calculations below were from

The 30 miles per gallon car creates 0.65 pounds of CO2 per mile.
The 50 miles per gallon car creates 0.39 pounds of CO2 per mile.
The Nissan Leaf creates 0.51 pounds of CO2 per mile.
The Tesla S creates 0.60 pounds of CO2 per mile.

The high percentage of coal used in the production of electricity in Wisconsin creates the higher CO2 footprint in the all-electric vehicles. A location with a grid that has higher natural gas use or, even better, higher percentage of renewable energy production for their power grid would have a lower CO2 footprint for the electric vehicles. For example; if the same Tesla S were used in San Diego California instead of Amherst Wisconsin, its footprint would be 0.26 pounds of CO2 instead of 0.60 pounds per mile, due to California's electric grid being powered by more renewable energies. The Nissan Leaf would create 0.22 pounds of CO2 per mile being powered in San Diego.

Those who make use of solar arrays to charge their electric vehicles are cutting down on their personal CO2 footprint drastically. For example, Jim’s Tesla Model S is only charged from his solar system, a zero-carbon footprint for his vehicle.

The last thing to compare is cost. While gas rates vary; electric rates between utility and time of day charging vary even more. The following are approximations for the cost of driving the vehicle 12,000 miles per year using the current $2.592 average cost of Wisconsin gas as of 11/3/17, and the current electric rates for Wisconsin Public Service and Central Wisconsin Electric Co-op.

A 30 mpg car will cost $1,036.80 per year to drive 12,000 miles.
A 50 mpg car will cost $622.08 per year to drive 12,000 miles.
A Leaf will cost $291.92 per year when powered by WPS ( $0.0997/kwh), or $401.43 per year powered by Central Wisconsin Co-op ( $0.1371/kwh). If the vehicle is only charged at night and uses WPS's time-of-use billing ($0.05767/kwh) it would be $168.86 per year.
The Tesla S will cost $382.85 per year when powered by WPS ( $0.0997), or $526.46 per year powered by Central Wisconsin Co-op ( $0.1371). If the vehicle is only charged at night and uses WPS's time-of-use billing ($0.05767/kwh) it would be $221.41 per year.

(Please note: while the costs for time-of-use billing lowers the cost of charging an electric vehicle at night, consumers need to understand their usage habits and how time-of-use billing will effect their bill before beginning a new billing program.)

Over time, the total cost of driving 12,000 miles per year, using WPS's electric rates and the current average gas rate without adjusting for increases in either of those costs looks like this:

30mpg 50 mpg Leaf Tesla S
1st year $1,036.80 $622.08 $359 $382.85
2nd year $2,073.60 $1,244.16 $583.84 $765.70
3rd year $3,110.40 $1,866.24 $875.76 $1,148.55
4th year $4,147.20 $2,488.32 $1,167.68 $1,531.40
5th year $5,184.00 $3,110.40 $1,459.60 $1,914.25
6th year $6,220.80 $3,732.48 $1,751.52 $2,297.10
7th year $7,257.60 $4,354.56 $2,043.44 $2,679.95
8th year $8,294.40 $4,976.64 $2,335.36 $3,062.80
9th year $9,331.20 $5,598.72 $2,627.28 $3,445.65
10th year $10,368.00 $6,220.80 $2,919.20 $3,828.50

10 years
of CO2

pounds of CO2
pounds of CO2
pounds of CO2*
pounds of CO2*

* This assumes charging in the 54406 zip code and that the utility's sources of power remains the same.

In comparison, the cost of fuel for the 30 mpg vehicle is more than twice that of the electric vehicles. While in Wisconsin the CO2 production is slightly less for an electric vehicle compared with a gas vehicle, for an electric grid such as California's the Leaf would have a 10-year CO2 production of about 26,400 pounds, which is significantly less.

As our options for electric vehicles expand, Wisconsinites need to encourage cleaner energy for our electric grid by influencing our government, as well as practicing distributed generation at our own homes in order to lower our collective CO2 footprint.,