Understanding true EV cost per mile
Why cost per mile is the clearest comparison metric
Annual cost figures depend heavily on how much someone drives, which makes them hard to compare across different households or vehicles. Cost per mile strips out that variable entirely, giving a consistent unit that works whether comparing your own EV against a gas vehicle or comparing your charging setup against someone else's in a completely different situation.
The blended rate is doing the real work here
Your true cost per mile depends on a blended electricity rate that weights your solar levelized cost and grid rate by how much of your charging actually comes from each source. An 80% solar offset at a $0.06 solar cost and 20% grid at $0.15 produces a blended rate of $0.078 per kWh, notably lower than the $0.15 grid-only rate but not zero, since a portion of charging still comes from the grid.
Why even grid-only EV charging usually beats gasoline
Electricity's energy-per-dollar is generally more favorable than gasoline's in most US and Canadian markets, so even an EV charging entirely from the grid at a typical residential rate usually costs less per mile than driving an equivalent gas vehicle, based on comparable fueleconomy.gov figures. Solar offset widens that gap further, but the underlying advantage exists independent of solar entirely.
What this comparison doesn't include
This calculator covers only the direct energy cost of driving, not the full picture of vehicle ownership. Purchase price, financing costs, like those modeled in the zero down loan total cost calculator, insurance, scheduled maintenance, and depreciation all factor into a complete total cost of ownership comparison, and those factors can shift the overall financial picture even when energy cost per mile clearly favors one vehicle type.
Following up on this result
Multiply your annual mileage by this cost-per-mile figure to estimate yearly charging cost, or take it to the EV solar payback vs gas savings comparison for a fuller financial picture including your added solar system cost. Related, and worth checking: the cost per kWh produced calculator.