Gas or Electric: Which one is cheaper for the Prius Prime!

Hypothetically, if I have access to a readily available public charger at a convenient place, I may go for it even at a higher cost than a gas station, but only if I can fully charge the battery in less than 5 min. If it is more convenient, then the higher cost is tolerable. We pay a higher price just for convenience for many other things. But the reality is that they are not available around where I live and the time it takes to charge is way too long. Other than at home or at work, I hardly ever spend 2.5 hours my car parked. Maybe if I am traveling and staying at a hotel where a public charger is available at parking, but that situation has not happened to me in the past two years.

 

Well I'm just south of San Fran, and I have Time Of Use (TOU) rates, and pay as little as 16 cents a kilowatt hour in the off-hours in summer. That's equivalent to about $1.70 a gallon for gas for a car that gets 50 mpg. Since gas in this area costs over $3.60 a gallon (occasionally topping $4/gallon), that's quite a big saving over running the Prime on gasoline.

Chargepoint doesn't determine the rate for its chargers--it is the owner of the Chargepoint station. Most are too expensive for a slow charging Prime. But my work has Chargepoint stations and they charge very little. There are a couple of free ones I can go to--one near a park where I can take long walks or sit and have lunch while charging, and another near movie theaters and a gym I frequent. Both are pretty well hidden so there's usually one open, though I've seen more and more Teslas show up, so I think the days of finding open free charging stations may soon be over.

 

I think you miscalculated something or your assumption is different from mine. How did you get $1.70 a gallon of gas equivalent from the $0.16/kWh electricity?

For charging PRIME to full, 6.1-6.6 kWh electricity is needed, depending on using L2 or L1, that would be $0.976-$1.056 at $0.16/kWh. If you assume EPA EV range of 25 miles and gas mileage is 50mpg, $0.976-$1.056 of full charged battery electricity used in EV mode is equivalent to half gallons of gas for the same distance to drive in HV mode. That would be equivalent to 2x($0.97-$1.056) of gas or $1.94/gal to $2.113/gal of gas. Yes, EV is still much cheaper than your current $3.60/gal gas for sure, but in a different region, you can find place gas is cheaper.

I pay $0.195/kWh for electricity and our gas has been below $2.50/gal for a while, this makes HV cheaper than EV. I still plug-in, but to justify my deed, I am wishing the gas price go up above $3 like in your area.

 

My calculations:
For my Prius Prime, it is about 6kWh for 28 miles (about what I get--yes it is a bit better than the EPA range). (6kWh/28 miles)*50= 10.7kWh for 50 miles.

$0.16/kWh*10.7kWh= $1.71 for 50 miles.

It is even cheaper if I charge at work ($0.12/kWh) or, of course, at one of the free chargers.

 

OK, I buy that. But to be fair, if you are using non-EPA EV range, then you should use your own MPG as well. I bet you are getting better than 50mpg. Mine during summer gets 65mpg easily on the gas-only operation calculated. MPG from the car tops 70mpg quite often. Of course, during summer I can also get an average ~35 miles EV range.

 

Love these plots - thanks! One question: Driving efficiency in mpg (ice) and driving efficiency on electric (mi / kWh) are both measuring the same thing - driving efficiency. So assuming one drives the same way regardless of power source, one could collapse these plots from a 3d contour plot to a simpler 2d plot, showing the line where the two energy sources are cost equivalent. I'm arguing that mpg efficiency and mi / kWh efficiency are not independent variables and thus this could / should be simplified?

Working it out based on EPA numbers (we could work it out it for the categories of aggressive / normal / efficient driving):

Prime = 54 mpg, 133 mpge. EPA says 1 gal of gas = 33.7 kWh. So the nominal EPA number for driving efficiency is 3.947 miles / kWh. Right around the 4 mi / kWh line in your plot.

This implies that unless the price of gas / gal < 13.681 * the price / kWh, it's cheaper to drive electric.

If the mpg and mi / kWh numbers changed the same way depending on driving style I think this equation would be the only one. Doesn't change any of your conclusions, and in fact your second post is pretty much this assumption mapped into nation-wide averages. So I guess I'm just suggesting that a plot with the single line might be useful in the first post.

 

These graphs are cool, but...

Is anyone else in southern California wondering why they stop at 25c per kWh? The cheapest rate for SDG&E is currently 29c!

 

With a Time of use Plan SDGE charges

Actually the super off peak rate on the Tome of Use Plan is 16 cents per Kwh. (that is midnight to 6 AM)
This works for meet, just set the charging schedule.

 

One can go nuts trying to decipher all the variations. I do know I tank up every 2-4 weeks, it is never any kind of burden. Every time I test my tailpipe it’s spotless. I also know that I, my son, are contributing to better air and besides all that the Prius is absolutely fun to drive! 3 Prii in the driveway now. I just love leaving all the traffic at the light, in EV mode. // Compare to standard stinkpots, Must tank up, once a week, Vehicle takes 20-40 gallons, Lt. trucks may need 60 gallons! My Prius needs 8-9 gal at each fill-up. Simply from a economic standpoint, ev/Hybrid makes sense. My 66 1300 CC bug also only required 50 liters to fill the tank ( 12.5 ) gal
But those were different times, circumstances and finances. It was also a revolutionary car. Fun to work on too.

 

TL;DR

Mike

 

At my old address, I was paying .075 / KWHr plus I installed 8 panels on my south facing side yard.
That was with SMUD, not PG&E. Actually now we have a sweeter deal, 24 panels, on the ground, and
my son pays! PG&E

 

Actually the super off peak rate on the Tome of Use Plan is 16 cents per Kwh. (that is midnight to 6 AM)
This works for meet, just set the charging schedule.[/QUOTE]

Time of Use, TOU, Pricing Plans, TOU Pricing Plans | San Diego Gas &amp; Electric

I don’t see a 16 cent tier.

 

I figured out that I pay about the same whether I drive in EV or HV mode - about $0.06 per mile.
I just drive and don't think too much about whether to drive EV or HV mode to save $$.
However, it seems I enjoy driving in EV mode way more than in HV mode. There is a a different & new feeling when driving with electric power only without the ICE coming on at all. And I've been driving ICE only cars and trucks for last 40+ years until I got my 2020 Prime just a couple weeks ago. Now when I see all those thousands of ICE only vehicles on the road on my commute, I feel they are ages behind and almost see $$ bills spewing out of their tail pipe!

 

Time of Use, TOU, Pricing Plans, TOU Pricing Plans | San Diego Gas &amp; Electric

I don’t see a 16 cent tier.[/QUOTE]

 

[/QUOTE]
Sorry it doesn't look like it posted right. try this:

 

Can you link the URL where the 16 cent chart is coming from? I only see the charts you posted above (the horizontal ones) showing 25 cents.

 

There can sure be variance in electric rates in California. Mine is a non-TimeOfUse plan, with $0.093/kwh for tier 1 (first 500 kwh/month), $0.143/kwh for tier 2 (all above 500kwh/month). City of Roseville Utilities. Makes the gasoline vs. electric decision real easy.

 

I wish I knew where I found them too. I cannot find them again. You are right, everything I see now is 24 or 25 cents at the lowest.

 

This discussion made me realize why electric vehicles aren't catching on that quickly in some parts. It's just not economical. Yet, they are perfect for the Canadian market. Here in Winnipeg, gas has just dipped below $1/L (probably among the lowest in the country), and electricity is $0.087/kWh. I figure I can charge up for about 65 cents, probably a whole dollar less than it would cost in gas for the 40 km (or about 2.5x less), even at this exceptionally low gas price.