I recently decided to make the step to an electric car and of course chose a Volt as in my mind it is the best alternative today. It is the only one that gives you a full electric vehicle but with the safety net of not being bound by the charging possibilities.
Given the technology is still young, that interest rates are low and that lease incentives on this car is high, I went for a 36 month lease.
Prior to making the jump, I ran a number of calculations to figure out my gas savings so I tough I would share this data for those who may be looking.
But let us be clear, as far as I am concerned, the cost saving is just a Bonus when you use a Volt. The satisfaction is much bigger than just that part
If someone catches any errors in my reasoning, please feel free to chime in. I also have a link to an excel sheet at the end so you can play with the numbers
Battery capacity: 16.5 kWh
But as pointed by TSquare, there is an SOC of 34.6% so
Actual usable battery: 10.8 kwh
My average miles per charge: 42 miles
As a result the number of miles I make on one kWh is:
Miles per charge / battery cap = 42 / 10.8 = 3.89 miles /kWh
Cost of gas:
Let us say you have a car that makes 26 miles per gallon like mine did:
Let us say you drive 12000 miles / year or 1000 mile /mth
Take a price per gallon of $4.5
Your gas consumption per month is:
Miles per month / Mile per gal = 1000 / 26 = 38.5 gal per month
Cost of gas per month is:
Gal per month x $ per gal = 38.5 x 4.5 = $173.1 of gas per month
Cost of Electricity:
Now evaluating the cost of electricity for the car depends on a lot of things and it can be a bit complex. To simplify it, you can assume you will be charging mostly during off peak hours and some during part peak (if this is the rate system you choose), or an EV rate if you use a separate meter for the car. You need to figure out the kWh price for these rates, and make sure it includes all the costs.
For me I decided to start without a 240 volts charger, so my charging time is 10 hours
Off peak is only 7 hours per day (midnight to 7AM), so at best I can charge 7 hours off peak, and 3 hours on part peak.
I figured out that my kWh cost are:
Off peak: $0.112 per KWh
Part Peak: $0.17 per kWh
So my average cost for charging
7hours off peak and 3 hours part peak is:
(0.112 x 7 +0.17 x 3)/10 = $0.13 per kWh
If you do 1000 mile per month the number of kWh per month is:
Miles per month / miles per kWh = 1000 / 3.89 = 257 kWh per month
Total electric charge per month = kWh per mth x $per kWh = 257 x 0.13 = $33.4 per month
Saving over gas per month: 173.1 – 33.4 = $139.7 monthly saving
Note: If you want to be very precise you would also need to calculate the impact of changing electrical rates on your regular consumption which is a bit more complicated. In my case I did estimate that going from an E1 PG&E schedule to an E9A would increase my other electrical cost by $9 reducing my savings down to $131 / month
Other comparison of cost of gas versus electric:
Looking at the cost of doing 100 miles.
With a car doing 26 miles per gallon and a gallon costing $4.5
Cost of 100 miles on gas:
(Nb of miles / Mile per gallon) x $per gallon = (100 / 26) x 4.5 = $17.31
Cost of 100 miles on electric:
(Nb of miles / Mile per kWh) x $ per kWh = (100 / 3.89) x 0.13 = $3.34
Cost ratio gas (26 mil/gal) over Volt on electric:
Gas is 5.18 times more expensive than electric on the Volt
Note: this ratio varies depending on the price of gas in your area, your cost [per kWh, the number of miles you do on a single Volt charge.
Now let us do the same calculation with a 38 miles per gallon which is the estimated consumption of a Volt while running the electric motor using the gas engine.
Cost of 100 miles on gas at 38mpg: (100 / 38) x 4.5 = $11.84
Cost of 100 miles on electric (same as before) : $3.34
Ratio between operating the Volt on gas or on electricity:
11.84 / 3.34 = 3.54 times more expensive
Looking at MPGe:
Based on calculation at the top of this post
Kwh you get for the price of one gallon: price of a gallon / price of a kWh = 4.5 / 0.13 = 34.65 kwh
(From the Wikipedia article http://en.wikipedia.org/wiki/Miles_p...ine_equivalent
EPA use 33.7kwh as equivalent to one gallon, so I am not far off with my 34.65 kWh <> one gallon)
Number of miles you do on these kWh:
Kwh for the price of 1 gal x miles per kWh = 34.65 x 3.89 = 135 miles on electric for the price of one gallon (my MPGe)
If you take the EPA calculation, they use:
1 MPGE = 0.0292 miles per kWh
My calculation at the top show I get 3.89 miles per Kwh, so my MPGe is:
3.89 / 0.0292 = 133.2 MPGe again pretty close.
Now in the same Wikipedia page referenced above they say the Volt is given for 36kwh for 100miles or 94 MPGe this corresponds to doing 2.78 miles per kWh (100/36) or driving 30 miles on one charge of 10.8 kWh.
So actually conservative numbers
You can find an excel sheet with all these numbers and calculation so you can run simulation based on different gas price, miles on a charge, PG&E rates etc…
It has a simplified sheet and the full original sheet. On the original sheet are my full PG&E calculation which may be hard to figure out, but I left them there just in case