This is just an "approximate" calculation to compare the driving cost in each mode Pure HV Mode $3.5/Gallon 60 Miles/Gallon $ per mile = 3.5/60 = $0.06/mile or $6 for 100 miles. Pure EV Mode $0.20/kWh 25 miles using about 7 KWh (which is about 80% of the total capacity of 8.8 kWh traction battery) $ per mile = (0.2/25) x 7= $0.06/mile or $6 for 100 miles There are many parameters that are constantly changing and would affect the outcome.
@noonm has done the math and produced graphs. Gas or Electric: Which one is cheaper for the Prius Prime! | PriusChat
Yeah, very close but at that rate of gas and electricity, EV is still slightly better. It is known that at the wall by OEM L1 takes ~6.5kWh to do 0 to 100% full charge. Using EPA standard 54mpg and 25miles EV range, or from most reported cases of PRIME efficiency, your EV range is about 1/2 of distance the car can drive with 1 gallon of gas. In my case the EV range in summer increase to 35 miles, but so does mpg on HV to ~70mpg. During winter EV range is down to 22 miles but so does mpg to ~44mpg. Use this 1/2 gallon HV distance for a full EV range rule, If you multiply the cost of electricity $0.20/kWh x 6.5 kWh= $1.30 If a gallon of gas is $3.50 (meaning $1.75 for a half gallon distance), then you are better off with EV economically.
For me, here in Austin TX, the numbers work out to about 4c per mile on gas (in town; more like 5c/mile on the highway) vs. 2.5c/mile charged from home. Austin Energy also has a program where (speaking in round numbers), for a $1/week, you can charge all you want around town, which thankfully includes my place of work. For me, miles driven that way come out to around 0.5c/mile. Arguably though, what’s even more valuable here is that I’m putting hardly any wear on my ICE, so at age 58 now, there’s a fair chance *I* will expire before our Prius Prime does!
My electricity ~$0.12/kWh and my car has cost me on average about $0.031/mi in fuel (electricity/gas).
You are spending only about 1/2 of what I'm spending here in SoCal - $0.06/ mile is fuel whether electric or gas...