Electricity cost more than gasoline these days.

BUT, and it's a big butt, the car charges quite nicely while driving. So one can continue switching modes when appropriate. I'm speaking of speeds of 35 - 55 mph, probably none of the above applies at 85 mph.

 

According to GasBuddy.com SC has the cheapest gas at around $2.00/gallon and CA tops off at $3.00/gallon so let's take the national average at $2.50/gallon.

HV cost: 50miles ($2.50) 25miles ($1.25)

EV cost: $1.25 / 6.5 kWh = $.19/kWh

Break even point is around $.19 so if your paying on average more than $.19/kWh then regular petroleum is cheaper than plugging in.

*Disclosure: these numbers are estimated by my personal research and I do not hold a PhD in mathematics.

 

Also, the convenience of charging right there vs your time & inconvenience factor to go home and charge factor into this, especially if home is level 1 charging.

 

I ran 1 complete tank without charging and I got 52 mpg (hand calculated). Currently gas here is 2.779. My car gets an average of 4.57 miles per kwh. I figure that 52/4.57=11.38 kwh to go 52 miles. I am on EV-B rate which is .1214 per kwh. 11.38 kwh costs $1.38 so I figure that EV is about 1/2 the cost of gas for me at this point.

 

That's the best way to figure it.

 

By inputing your local gas $2.78/gallon and by dividing your 11.38kWh by two equals the amount of one full charge 5.69kWh (about 25 mile EV range):

HV cost: 50miles ($2.78) 25miles ($1.38)

EV cost: $1.38 / 5.69 kWh = $.24 / kWh

So your break even point is around $.24 per kWh. And if your paying $.12 per kWh that is exactly half of what you will pay compared to petro.

 

So... if your numbers / estimates are more-or-less correct, and if I'm NOT "misinterpreting" what you say... does this mean that once we have our Prime / "Premium" our driving costs in EV will be lower than HV costs?

Around here, gas is currently $2.35-ish, and the cost per kWh from our most recent electric bill was:

A) $.143 ... that's when taking the TOTAL of our most recent electric bill (including ALL "Rider Fees", taxes, etc.) divided by the number of kWh usage - 643 - for the month... OR...

B) $.073 ... that's when taking ONLY the "Total Energy Charges" (being charged for some kWh @ $.0929 / for some kWh @ $.0542) divided by the number of kWh usage - 643 - for the month.

PS: I don't have a PhD in mathematics either... snicker....

 

A) is what I used to calculate my own cost. My Xcel Energy bill charges for my total electricity $.13 per kWh in Denver, Colorado. This number varies by usage, fees, taxes and it depends on what county you live in.

Prius Prime battery is 8.8 kWh total but Toyota designed the HV mode to kick in when the battery reaches 25% capacity meaning when we charge from empty to full it's actually 6.5-6.6 kWh not the 8.8 total kWh.

Hope this helps those of you paying more than $.20 per kWh you should just fill up with regular gas.

I did pass Calculus 1 in college

 

Maybe this will make it easier for people to understand relating to the original post:

HV mode (burning gasoline)
California: $3.00/gallon divide by 52mpg = $.057 per mile
South Carolina: $2.00/gallon divide by 52mpg = $.038 per mile

EV mode (using electricity)
$.20/kWh multiply by 6.6 kWh = $1.32 divide by 25 miles per charge = $.052 per mile
$.10/kWh multiply by 6.6 kWh = $.66 divide by 25 miles per charge = $.026 per mile

Toyota Land Cruiser: $3.00/gallon divide by 15mpg = $.20 per mile!

 

Prius Prime battery is 8.8 kWh total but Toyota designed the HV mode to kick in when the battery reaches 25% capacity meaning when we charge from empty to full it's actually 6.5-6.6 kWh not the 8.8 total kWh.

6.6x4.57 = 30.16 miles EV range. I've been getting about 32 and others I've seen as high as 37mile. Probably hypermiling at 40mph.

 

The SOC (state of charge) ranges from around 21% (in HV mode) to around 85%. Factor in around 85% charging efficiency, and you get the observe 6.5kWh from the wall. 100% SOC is not good for a LiIon battery.

 

I don't have a Prime, so I only care about gas prices. Even though I live in California, I drive to Arizona every week, and buy most of my fuel there (Chevron/Texaco only). Right now Arizona gas is about $2.35 a gallon, in Cali it's $3.20 or higher.

For Prime owners, a graph showing break even costs would be nice. Or an online calculator. But it would probably take at least a passing grade in Calculus 1 to figure out the math .

 

Courtesy of Lee Jay in case you haven't seen it.

 

FWIW, I've been calculating my kWh used for the past 10 days and the average is 6.28. So I use that to figure my cost.

 

Thanks for posting / sharing this again... that's good to know, AND it was very nice of Lee Jay to do the math for people like me!

 

As others have alluded, we’re only using about 6KWh of the battery’s total capacity, and most of us are seeing, for now at least, more like 32 miles from that. My P.Prime itself reports about 4.7 miles/KWh, which is a whole lot better than the 2.5 number from your estimates.

Granted, that efficiency will gradually reduce over time, as the battery ages.

 

As others have alluded, we’re only using about 6KWh of the battery’s total capacity, and most of us are seeing, for now at least, more like 32 miles from that. My P.Prime itself reports about 4.7 miles/KWh, which is a whole lot better than the 2.5 number from your estimates.

Granted, that efficiency will gradually reduce over time, as the battery ages.

 

Yes & No - if I may respectfully pick a couple nits.
Even though the traction pack will lose capacity, while running Ev, its efficiency will remain the same. Similarly the ice efficiency will remain the same. However, with less traction capacity the vehicle will start using more of the ice, so your miles of EV drive time will decrease. IOW, as your traction pack ages, if you keep driving less & less miles, you can maintain the same efficiency, you will just have to charge up a whole lot more, to avoid using more & more ice .

.

 

I seem to recall that the internal resistance of Li-Co batteries does gradually increase over time, which would reduce efficiency. However, now that I think of it, that might be more associated with DC quick-charging than normal use, though...

I would expect ICE efficiency to decrease gradually as well from wear, although not by a whole lot, assuming that it is well-maintained.

 

I seem to recall that the internal resistance of Li-Co batteries does gradually increase over time, which would reduce efficiency. However, now that I think of it, that might be more associated with DC quick-charging than normal use, though...

I would expect ICE efficiency to decrease gradually as well from wear, although not by a whole lot, assuming that it is well-maintained.

 

My 30-year-old ICE got better mileage when 30 than when new, and not by an insignificant amount (31 -> 35).