Since we're going down the alternative-fuel route, here's another option:
- A Ford Taurus powered by compressed natural gas (CNG) gets 21 miles per therm.
(this is a substantial car, not a wispy econo-box). (see
this Kansas state comparison of alternative-fuel vehicles).
- The conversion of a standard gasoline car to CNG costs $4000 to $5000. These conversions can run on
either gasoline OR CNG. USe the gasoline when you are on long trips away from your available high-pressure NG, and run off NG the other 95% of the time. The high-pressure pump to let you fill the car at home costs another couple grand.
- The average price for a therm of NG in the US is about $1.80 (see
this chart. A therm = approx 100 cubic feet, the costs shown are for 1000 cu ft). So, your fuel cost would be approx 1.80/21 = 8.6 cents per mile.
The average cost for electricity in the US is
10.6 cents per kWh . So, if the Tesla roadster has a battery with a 56 kWh capacity, it costs $5.94 to "fill the tank", and it will go 225 miles. That's 2.6 cents per mile. Oh, wait, here's some small print we should see: The battery is good for "> 500 recharges". Yikes! That's supposed to be okay? Replacing the battery every three years is going to cost how much?
In comparison, a gasoline powered car (25 mpg, gasoline at $4) costs 16 cents per mile in fuel.
The CNG conversion can make a lot of sense if you want/need a real car (that can carry 4 people and groceries), if you might want to tow a light trailer, if you might want to take it on trips and be able to fill it with gasoline, if you'd like to save approx 1/2 in fuel costs, and be able to get it repaired at any regular mechanic. Total costs (conversion + high pressure pump) of about $6000 over the cost of a "regular" car (and the slight loss of utility from the space taken by the CNG tank). It would take about 75,000 miles of driving to break even for these costs--after that, it's all money in the bank.
It's not for everybody, but it could make sense for a lot of folks.