Mathematicians needed! PiP Charge cost vs Gas

I hit the gas station once a month or every 1000 miles.


iPad ? HD

 

...maybe but little longer time perhaps

The next PiP's induction charging is sounding better to me, although I probably trash talked it when I first heard it.

 

No need to include the gas per EPA, the ICE did not start.
You are doing 143 MPGe in those short trips, that is 50% better than EPA estimate of 95 MPGe for the average driver!

 

eprice ($/kWh) * ev_efficiency (wall kWh/mi) + gprice($/gal) * ev_gas_efficiency(gal/mi) < (gprice ($/gal)/hv_efficiency(mpg))

Rearrange

eprice * ev_efficiency < gprice / hv_efficiency - gprice * ev_gas_efficiency
eprice * ev_efficiency < gprice ( 1/hv_efficiency - ev_gas_efficiency )
eprice < gprice ( 1/hv_efficiency - ev_gas_efficiency ) / ev_efficiency

Long term you may have to make gprice = gas - gas_taxes to exclude the tax dodging.

Some of the variables depends on where you are and driving patterns so we don't _really_ have enough information, but including the taxes and using EPA ratings for the PiP:

EPA:
- Blending: (.2 gal/100 mi of gas plus 29 kw-hrs/100 mi of electricity ) (Note that EPA electricity ratings are wall-to-wheel)
- Hybrid: Combined: 50 MPG
gprice = 3.33
hv_efficiency = 50
ev_gas_efficiency = (0.2/100)
ev_efficiency = (29/100)

Plug in the numbers:
eprice < 3.33*(1/50-(0.2/100))/(29/100)
=> eprice < $0.20668966/kWh

To paraphrase: Algebra. It works, bitches! (The real challenge for most people is getting from the information to the formula. I'm a math major so I guess you could call me a mathematician, but this stuff is "high school" math. In fact, it's not really even high school math. In the UK at least unless you were in a bottom set you'd have learned the math for this by the age of 14.)
EDIT: OK, I mentioned this to my wife and her reaction was "You said WHAT!?" (She's a community college tutor (and advisor), providing additional support in math and science, so naturally she was aghast). I'm sorry, my remarks about it being "high school math" weren't meant as an insult, they were meant to say "Don't fear math, you CAN do this stuff."

 

I use a gas station right on my daly route!

 

Follow the maths, just a bit unsure about the starting point. The left-hand side of the equation is calculating EV cost, but includes some gas, because in EV mode you will blend in a small amount of gas with the EV mileage, is that right? Doesn't generally happen with me, but I suppose that is because I am normally in the European EV City mode when driving on EV. So the 100 miles traveled takes a COMBINATION of 0.2 US gal fuel plus 29kw/h?

However, usbseawolf2000's quick 'n dirty method is much more appealing, and if you are going to use the EPA figures, everything other than gas price and electricity price stays constant. However, this calculation suggests the multiplier should be (roughly) 16 rather than 12. That in turn suggests over five charges to do 50 miles, and indeed the EPA figures are 9.7 charges to do what is really 90 miles (allowing 10 miles for the 0.2 gallons).

That seems a lot lower than most people are getting as an average. I'm certainly still getting 11 even with temps down now to mid 40s F, and, albeit in ECO, with one acceleration up to freeway speed, combined with a third of the EV mileage being at around 50mph and the rest tending to be stop start. I suppose this is the area where it helps that in Europe we can't do more than around 53-54 (real) without the ICE kicking in.

 

The EPA method does include 0.2 gal per 100 miles due to an aggressive driving profile even though their trips are only 11 miles . It seems appropriate to include that comparison, at least as a matter of interest, since it implies that their estimate is probably reasonable for their driving profile. Of course I don't believe that "average" PiP driver uses their EV miles that way

 

Definitely sounds cool, but I can't imagine how much those would cost to have one put in your garage.

Also, not sure it's a done deal. I thought it was just kind of a rumor still.

 

You can choose to drive PiP in city traffic so it it an EV. EPA label did not offer/indicate that choice.

If you did not use gas in your real world commute, EPA label/figure is not applicable to you.

 

I don't understand your comment. I don't commute. I drive the car, sometimes I use gas, sometimes I don't. I calculate my mpg-e based on an equivalent 1 gallon of gas for each 33.7 kWh. That's what most folks is the "fair" way to make the calculation.

 

I think usbseawolf2000 was referring (as I did) to your post #20 here where you reported 8 EV-only trips and compared results to EPA estimate for the first 11 miles.
But it is up to you how you are making your calculation.

 

I don't see how it makes any difference which part of the battery you are using. SOC gives a good representation of much energy you used for how many miles and the kill-a-watt meter tells you how much energy it took to recharge. Of course, measurements for larger changes will tend to be more accurate. Its not a contest just an estimate of how it all works.

 

One can say anything with math. In fact, you just did. All of your text was converted to math in order to transmit it to where we can read it.

Plus, all those things you state are needed are all math. If it happens that you personally can't convert all those things into an equation, please don't try to put that limit on the rest of us.

 

Did I hear my name?...

A Prius Plugin uses about 0.30 kWh to go a mile, and about 0.02 Gallons of gas to go a similar mile.
So, (0.30 / 0.02 = 15 kWh / Gallon*) if your electricity costs (per kWh) times 15 is less than the cost of gas (per gallon), you are saving money. In your example, of $3.33 / gallon gas, you are saving if your electricity costs less than $0.22 per kWh ($3.33 / 15 = $0.222).

For every three cents cheaper your electricity is than the break even stated above, you save about $0.01 per mile. For example, I pay about 6 cents less per kWh, and would thus save 2 cents per mile. Multiplied by a projected 200,000 miles per car, and an electric percentage of 50%, I would save $2,000 over the life of the car. Your results will no doubt differ.

* - This is NOT the conversion of electricity to gasoline by energy content, but rather the relative costs based on energy content AND efficiency.

 

It should be noted that in general, if you are grid-tied, net-metered, not on TOU, and not near the limit, using your solar electricity costs the same as regular electricity. In other words, you are using electricity that could have gone to reducing your electric bill, at the going rate. Solar electric is only free for you to use, if you have no other way of monetizing it (which is a condition you don't really want).

 

This is a YMMV, depending how the value of PV kWh is calculated. It is quite common for people to receive more money for a home generated kWh than they pay for it's consumption.

As one example, my utility PNM in New Mexico is currently paying new installations of home PV 4 cents a kWh to generate and consume each kWh

 

Somewhat true... Only thing I take issue with is when you say, "Solar Electric is only free for you to use....". Tain't free as You (I) have to pay for the cost of the Solar Voltaic System... However... Since my Electric from the grid cost 12¢ and Fossilized Dinosaur Dung is about $3.60 a gallon I figure every kW I use from my panels in the PiP is saving me 24¢ of crap I don't want to use anyway. By using Solar Electric to charge the PiP to amortize the cost of the system I am saving more than if I was just buying it from the grid. At least that's the way I like think about it. Yeah, I know that is a kWh I now have to buy from the power company, but since I am on a 100% green plan, I just don't worry about it.

 

I really did include enough caveats. Net-metering implies same price going in as out, Non-TOU implies no difference in price depending on time.

If one is on a feed-in-tariff plan, and a time of use plan, then one is golden. Not the norm in the US, by any means.

 

PUT a limit???
I was trying to free the OP from the limitations of trying to justify a Pip with math.
The eco-chic in my beloved community are always bellyaching that "it's not about the money." which I believe is the truth.
People generally buy Pips for either very selfish or very selfless reasons.
Just yesterday I was looking on line to try and determine which dealership has which base model pip close enough to me because my daily commute is about to shrink from 10 miles to 3 miles....AND I can charge on both ends.
I just think it would be cool to not have to buy gas from week to week for my bounce back and forth to work.....but it's not math.
It's emotion.

You're absolutely correct about one thing.
Math is like data...or facts if you wish.
You can prove anything with statistics...and you can have a fact-filled 5,000 word article that is still as screwed up as a football bat.

YMMV....
(your math may vary)

 

Net metering is meant to imply a bank (or lossless battery) analogy. You are allowed to time shift your production. However, nothing precludes the producer from receiving extra money from the utiilty for the generated energy, regardless whether the utility ever sees even one joule.