Update: I was not aware of
Tesla’s website has a calculator to determine how much it costs to charge a Model S. In theory one reason to buy an electric car is that it cost less to charge vs. filling an Internal Combustion Engine (ICE) car with gas or diesel. However at least in Northern California, where there are a large number of Model S’ being driven, if one were to charge a Model S at home it could cost more for the electricity than the equivalent amount of gas at a gas station.
In Northern California the average price for regular gasoline was $2.295 a gallon for the week of February 22. Mid-grade cost $$2.415 per gallon and Premium was $2.528. The average miles per gallon for a car or light truck has increased from 22.4 miles per gallon in 2011 to 23.6 miles in 2012 to 24.1 in 2013 to 25.5 in May 2015. Tesla’s website starting assumption is 40 miles for a car to be driven in a day which at 25.5 miles per gallon and a cost of $2.295 per gallon would cost $3.60 to refill.
The key figure on Tesla’s website when calculating how much it costs to charge a Model S is the price per kilo Watt hour (kWh). The website has the national average at $0.12 per kWh which may be a little low (the US Energy Information Administration, EIA, had it at $0.1273 in November last year) but overall close enough. For some additional detail here is a link to the average cost of electricity by state and customer type by the EIA. It is a bit interesting that Tesla is optimistic on electricity charges similar to its financial guidance which it has historically missed.
However at least in Northern California where I live electricity costs can be much higher. PG&E has four pricing tiers for electricity starting at $0.18151 per kWh for baseline amounts going up to $0.34876 per kWh for Tier 4 at 201% of the baseline. A Model S’ electricity should be incremental to the amount a residence uses so would probably be billed at the highest tier as it doesn’t take much to get to 201% of the baseline amount.
The website’s assumptions are:
- 40 miles driven per day
- $0.12 per kWh which is the national average
- Using a 240 volt outlet
Results in:
- 1 hour and 21 minutes to charge
- using 13.2 kWh
- costs $1.58 to charge your Tesla
If you use a 110 volt outlet it results in:
- 12 hours and 16 minutes to charge
- using 17.7 kWh
- costing $2.12 to charge your Tesla
However when you calculate the cost to recharge the 40 miles using the Tier 4 $0.34876 per kWh price the refueling costs would be:
- $4.60 when using a 240 volt outlet
- $6.17 when using a 110 volt outlet
Which is significantly higher than the $3.60 in gas costs. Gas costs are lower than they have been due to oil prices collapsing the past 18 months so the difference should lessen but electricity costs should increase.
Additional information regarding PG&E electricity rates and their impact on my analysis (this was added after the article was first published)
PG&E has two rates for residences that have Electric Vehicles, EV-A and EV-B. EV-B is for when a house installs an additional meter for just charging an electric car.
The two EV rates are not tiered (so it doesn’t matter how much you use) but they are time-of-use with 11 pm to 7 am the lowest cost timeframes (which is when most people would charge an electric vehicle). There is also a slight difference between Summer and Winter rates with Summer having the lower cost.
There is also a slight difference between Summer and Winter rates with Summer having the lower cost. For the following calculations I’m using the EV-B Summer Off-Peak rate of $0.10893 per kWh which is the lowest Off-Peak rate available.
- The cost to recharge a Model S after 40 miles using a 240 volt outlet is $1.44 and using a 110 volt outlet is $1.93 at the Off-Peak rate.
- This compares very favorably to an ICE car that gets the average 25.5 miles per gallon since it would cost $3.97 with Premium gas and only decreases to $3.60 with regular gas. These costs are also low since the price of gas has decreased over the past year.
- Assuming that gas increases to $3.50 per gallon and that the ICE car’s mileage is 20 miles per gallon the cost to refuel would be $7.00.
- While it would not be the typical use case if an electric vehicle is charged at the lowest Peak rate of $0.2992 per kWh (EV-B Winter rate) the cost does increase to $3.95 using a 240 volt outlet and $5.30 for a 110 volt outlet.
Model 3 impact
I believe most people don’t realize how much a kWh costs and wouldn’t estimate how much it would cost to charge a Tesla. While having a Model S cost more to fuel than a similar amount of gasoline probably won’t deter its buyers if there remains a difference when the Model 3 starts shipping it could crimp demand for them.
