Plug in MPG?

[jerryliebler]

I recently became the owner of my second plug in Prius. The first, a 2012 model was "t-boned" to death by a not so great driver. My new ride is a MY 2013 that will shortly have 40,000 miles. I had several "issues" with this car's poor, relative to my old car, fuel economy. I do believe I've remedied the problem(s). In looking through the fuel logs of similar cars I see a huge variation in what is reported as MPG. Most seem to completely ignore the electrical energy from being plugged in. Some include some of the data as notes. To me ignoring electrical input is outright dishonest. At least add the equivalent gasoline quantity ((Kilowatt hours/33.7KWhr/gal)*charging efficiency) to the gasoline added to the tank and report MPGE. If one does this and has 100% EV use and drives the EPA cycle they will get 105 MPGE. Similarly EPA "benchmark" performance with no plug in electricity is 50 MPG.

[luv2spd]

I agree with you, with the MPGs listed here for plug-ins, you have to take the numbers with a grain of salt because the electricity used is not taken into account. If you have a Chevy Volt and are willing to pay for OnStar; this website shows the true MPGe for your car. If you use a plug-in; you can still use this site to see how much fuel you are actually using and maybe use the "Notes" section to enter your electricity consumption.

Volt Stats! Tracking real world usage of Chevy Volts in the wild...

[jerryliebler]

I guess my real question is what should I record here? The PIP can easily track electrical use per tank and it can track "EV" miles along with HV miles per tank. The trip odometer records the total miles on both fuels. The simplest, relatively honest, report would add equivalent electrical energy to pump gallons and report MPGE. This will
vary with the percentage of energy from plugging in as electricity is over twice as efficient compared to gas. Thus PIP drivers who drive mostly ON battery will show much better results than those who use a higher percentage of gas miles. This can be "normalised" by separately computing economy for HV and EV, comparing each to the EPA benchmark and computing a weighted average "performance to benchmark" score. This approach essentially eliminates the advantage of a higher EV/HV ratio. One could go a step further and compute an equivalent performance to benchmark for gas only, or electricity only by multiplying the weighted average score times the gas only benchmark or electricity only benchmark. For my latest tank I could report: 64.94MPG (what most seem to do) ignoring Electricity used. 60.34 MPGE by adding the gasoline equivalent of electricity to pump gallons. 54.23 MPG just using the HV miles. 56.25 MPG equivalent performance to benchmark times benchmark for gas only. 118.13 equivalent performance to benchmark times EV benchmark.

[luv2spd]

If I were you I would just enter the MPG for the fuel only and put the electricity used in the "Notes" section with each fill up. This website only tracks MPG and not MPGe; so if you enter MPGe it might be confusing to some people.

[SteveMak]

I agree with luv2spd's "grain of salt" statement. Look at non-PHEV numbers for a specific engine, and you'll still see wild variances. Even with my car, driven my one person, with a pretty consistent driving style, I get significant tank-to-tank variances due to weather, traffic jams vs clear sailing, longer highway trips, etc.

Although I don't view Fuelly as The Holy Truth, I still find it very useful. But i get your point about the PHEV plug-in factor, in itself, adding yet another dimension of considerable variance.

[Draigflag]

I hate how they still use MPG for cars with 2 different drive trains and/or fuels, makes no sense. Like I keep seeing Nissan Leaf with a "200+ MPG" figure, didn't realise you could buy electricity by the gallon ha.

[SteveMak]

Originally Posted by Draigflag

I hate how they still use MPG for cars with 2 different drive trains and/or fuels, makes no sense. Like I keep seeing Nissan Leaf with a "200+ MPG" figure, didn't realise you could buy electricity by the gallon ha.

You can tell Fuelly (and other sites) were designed with only internal combustion engines in mind, and they have not been updated to take plug-in hybrids and EVs into account.

And even in those cases, is there a way for a car to report "I've taken on 22.65 kilowatt hours of electricity at X cents per kWH"? In many locales, electricity rates change depending on time of day usage, and even volume (first X kWH @ $0.xx, next Y kWH @ $0.yy), so it would be difficult to enter true electrical costs.

[trollbait]

You could set up a profile for just HV miles, one for just EV miles, and another for both.

The real issue is making sure the dash display is actually what you think it is. The HV to EV ratio is actually what you think it is; the ratio of what mode the car is in. The new Prime on the other hand reports anytime the ICE shuts off as EV miles. So the EV percentage includes electricity used from the grid and made from gasoline.

The other thing is that the dash display is likely using how electricity was used from the battery for calculations. Because of charging losses, that isn't the electricity that was put into the car. You need a Kill-a-Watt on the EVSE that came with the car, or a level 2 EVSE that tracks kWh used. The EPA numbers assume an average charging loss from a level 2 unit.

[jerryliebler]

Originally Posted by trollbait

You could set up a profile for just HV miles, one for just EV miles, and another for both.

The real issue is making sure the dash display is actually what you think it is. The HV to EV ratio is actually what you think it is; the ratio of what mode the car is in. The new Prime on the other hand reports anytime the ICE shuts off as EV miles. So the EV percentage includes electricity used from the grid and made from gasoline.

The other thing is that the dash display is likely using how electricity was used from the battery for calculations. Because of charging losses, that isn't the electricity that was put into the car. You need a Kill-a-Watt on the EVSE that came with the car, or a level 2 EVSE that tracks kWh used. The EPA numbers assume an average charging loss from a level 2 unit.

After trying to enter my most recent tank, as a starting point, I am inclined to simply give up! This site computes miles by the difference of odometer readings and gallons are what is input meaning that the only possible correction would be to input "adjusted" gallons (adding the electrical input equivalent). Even if everybody did this, it would still look like those who can use more electricity are better "hypermilers". I'm quite sure the car does the right thing in recording as EV miles miles driven in EV mode (even if the ICE is on) and HV miles when the HV mode is selected (even if battery power is used) I know this because I start most trips in HV mode and use no EV miles even though I use some battery power during warm up for example. I also have dramatically inflated my EV miles by selecting EV mode to kill the ICE in a downhill glide beginning at 62MPH. I've changed how I enter the high speed glide and now after confirming ICE off I shift to N then go back to HV mode. Unfortunately N doesn't allow regen but at least the miles are scored more appropriately. Regrettably the KW use reported by the car is only whole numbers I'm going to deploy my Kill-A-Watt to get better data on charge input. FWIW The spread sheet at Prius Chat records and computes the "right stuff" to compare hyper-miling success against a peer group of first gen PIPs
If the Prime behaves as you say, I do believe Toyota screwed up and gave me another reason not to "upgrade"!

[Draigflag]

You're always going to find that issue with plug ins sadly. Check out the other topic regarding Chevy Volt mileage stats, some owners getting 15,000 MPG, others getting 32 MPG, all depends on how often you can charge, and the length of your journeys.