When I was still on the mainland, gas briefly went over six dollars a gallon. I got curious about how far Joulee the Free Salvage Tesla would go on $6.00 worth of electricity.
The calculation goes like this. I was paying about 12¢/kWh for electricity. Overall, Joulee uses about 325 Watt-hours per mile. So the equivalent of a gallon of gas would be $6/$.12/kWh = 50kWh/.325kWh/mile = 154 miles/gallon. Not too bad.
Figuring the equivalent cost of “fuel” here is a bit more challenging. If I were on the grid, I’d be paying about 50¢/kWh. But I get my electricity from sunshine, so you could say that the cost is zero. Of course, I had to buy the solar equipment, but that was all covered by a Federal tax credit. That credit is done, though, so eventually (20 years or so) I’ll have to replace that equipment. So it’s hard to say, but to a first approximation I’m driving on sunshine for free.
For the most part, our solar plant is capacious enough that we can just act as though we’re on-grid. We have an electric car, electric clothes dryer, electric hot water, electric kitchen appliances, and on and on. We usually don’t have to think much about it. Occasionally, though, we’ll do a lot of driving AND have a stretch of dark, rainy days. I’m not complaining, the rain is nice, but it doesn’t generate power. So then we have to make a decision. Do we run the backup generator to charge the car, effectively turning our EV back into a gasoline-powered car? Or do we just take Timmy the Titan, our diesel-powered pickup truck?
I once took our backup generator, which had never had gasoline in it (the few times I ran it on the mainland, I used propane). I added exactly five gallons of gasoline. I charged the car from the generator until it had used up the whole five gallons. It added 43% to the 85 kWh battery, or 36.6 kWh. That would give us 113 miles of range, or 22.6 mpg. Timmy gets close to 24 miles on a gallon of diesel, but diesel costs a bit more here than gasoline, so I’m guessing it’s pretty close to even.
More important, though, is that we’d never be running on 100% gasoline-derived electricity. At most, we’ve only needed to add 15-20% charge to the car, so even when we have to use gasoline-sourced power, we’re still running 80% on free sunshine.
If we didn’t have solar, though, it would make no sense to drive an EV that we charge with a gasoline-fired generator.
—2p