Average watts per mile

Discussion in 'Clarity' started by Tim66, Aug 27, 2019.

  1. Tim66

    Tim66 Active Member

    Clarity Phev

    I'm delving into my Juicebox settings and found an entry for Average watts per mile. Is there a way to calculate that number using the information provided by the car or some other method? I searched this forum but didn't see anything directly addressing this issue.

  2. Sandroad

    Sandroad Well-Known Member Subscriber

    It would be easy to calculate manually, just like manual calculation of mpg. Fully charge, drive and record miles driven, fully charge again and record Kws used, then divide. Given the factory numbers, it should be ballpark 3.3 miles/Kw.
    ClarityDoc likes this.
  3. Steven B

    Steven B Active Member

    Yes, based on EPA 110mpge = Estimated 306 W/mi.
  4. bpratt

    bpratt Active Member

    I have tracked my miles per KWh since I purchased the car in December 2017. My average in the winter is about 2.5 miles per KWh and about 4.0 in the summer. My lowest average month was December 2018 at 2.36. My highest average month was October 2018 at 4.23.
  5. KentuckyKen

    KentuckyKen Well-Known Member

    This metric is usually expressed as kW-hrs per 100 miles. This is what the EPA mandates be put on the Mulroney sticker when you buy a new EV. It’s also easier for most to understand kWs instead of Watts since that is what people are billed for on their utility bills.

    The EPA rating for the Clarity is 31 kW-hrs per 100 miles or 0.31 W-hrs/mile in your reckoning.
    This summer with temps in the 80s and 90s F with ac on, I’m consistently using 22 to 24 kW-hrs per 100 miles.

    The easiest way to calculate this is to set your Trip A to reset at each charging event and record. Then just be sure to charge fully to 100% SOC and all you have to do is take the KW-hrs consumed from your EVSE and divide by the miles from Trip A times 100 to Get kW-hrs per 100 miles.

    You can also calculate miles per kW-hr and multiply that by 33.7 kW-hrs/gal to get MPGe. (I think that is how the EPA does it)

    And the trivia question for today is why is W, V, and A capitalized?
    Because these units stand for the names of the men who worked them out.
    James Watt, Scottish
    Alessandro Volta, Italian
    Andre-Marie Ampere, French
    Elm, David Towle, insightman and 4 others like this.
  6. sniwallof

    sniwallof Active Member

    The one I constantly struggle with is the "k" in kW. I know it's MW for MegaWatts (maybe to distinguish over m for milli?, but what about micro? (I guess the Greek symbol works), but is it kW or KW?

    Maybe I just got lucky on my first Google - looks like lower case kW

    https://www.nist.gov/pml/weights-and-measures/writing-metric-units#targetText=The prefix "kilo" stands for,a "kilogram" of something.

    Physical Measurement Laboratory, WEIGHTS AND MEASURES, Writing with Metric Units, Capitalization, Prefixes

    Prefixes: Symbols of prefixes that mean a million or more are capitalized and those less than a million are lower case (M for mega (millions), m for milli (thousandths)).
    Last edited: Aug 27, 2019
    KentuckyKen likes this.
  7. bpratt

    bpratt Active Member

    Since we are use to MPG or miles per gallon, to me it made sense to use MPK or miles per kilowatt hour. Since my power costs me about 8 cents per kilowatt hour, I know I can drive a mile for 2 cents in the summer when I am getting 4 miles per kilowatt hour.
    Mark W likes this.
  8. Sandroad

    Sandroad Well-Known Member Subscriber

  9. Please, somebody, edit the title for this thread. It has to be Watt-hrs or kW-hrs, not Watts.

    Here comes cwerdna!

    (Oh, that's right, he's on another forum)
    KentuckyKen likes this.
  10. Ray B

    Ray B Active Member

    And it is at this stage where I'll point out how amusing it is that we describe energy units with a time dimension. I guess it is kind of like when we ask how far it is to a place and people respond "it's about a 2 hours away". :)
  11. This is because a watt is a joule per second. It would probably be less confusing if we expressed energy in megajoules instead of kilowatt hours.
    Ray B likes this.
  12. 2002

    2002 Well-Known Member

    Interestingly in boating fuel consumption is typically measured in GPH (gallons per hour). In aviation either GPH or PPH (pounds per hour).
    sniwallof likes this.
  13. Clarity_Newbie

    Clarity_Newbie Active Member


    The Clarity I drive exhibits numbers similar to yours using the methodology you used.
    Winter = 2.9 m/kWh. Summer = 4.27 m/kWh. With the 3.93 m/kWh the mean.

    For full disclosure...I do discount the kWh 3 % for efficiency loss during charging.

    Good info...hopefully others will share numbers to see the range...would be interesting.
    Last edited: Aug 29, 2019
  14. Clarity_Newbie

    Clarity_Newbie Active Member


    The Clarity I drive exhibits the same trend per 100 miles using your methodology.

    I cipher ~23 kWh = 100 miles. Summer time, temps 80-90's, AC on...always set to 71 degrees.

    Normal mode 95% of the time...sport mode 5%. 80/20 split local vs highway miles. Sedate driving style.

    For full disclosure...I do discount the kWh 3 % for efficiency loss during charging.

    Good info...hopefully others will share numbers to see the range...would be interesting.
    KentuckyKen likes this.
  15. Sandroad

    Sandroad Well-Known Member Subscriber

    But,but,but.....there are a lot more losses eventually on the way to the armature of the motor! I think it’s overall watts used and discounts are not allowed ;)
    KentuckyKen likes this.
  16. KentuckyKen

    KentuckyKen Well-Known Member

    I agree. The losses from on board charger, extension cords, battery cooling, ac and heater usage, etc. are part and parcel to acquiring and using the energy needed to drive the car. No discounts allowed just like we don’t subtract out the state and federal tax on every gal of gas when computing MPG.
    And the flip side of that coin is to subtract out any HV and System Check, etc. gas miles from the MPGe calculation. Only then can you get a true and accurate number for the kWh/miles efficiency in EV driving.

    I’ve kept track of every mile, kWh, gal, and miles in HV. I use these records to compute mile/kWh, MPGe, kWh/100 miles, and MPG (since my HV Tripp’s have been few). This way I know how the Clarity performs in each power source as to efficiency and cost per mile and year. I also know the overall cost per mile and year by combining EVSE reported kWhs, gas pump receipts, and total odometer miles.

    However, when “evangelizing” at Drive Electric Week and EVolveKY EV events, I found that the general public doesn’t understand all these metics. What does get their attention is when I tell them I get 140 MPGe in the summer and 110 in the winter and that is like paying less than 50 cents a gal for gas.

    That and having no range anxiety seems to make the biggest impression. (Interior room, comfort, and trunk space seem to be next in order of what impresses people unfamiliar with EVs.) I found very, very few were interested in the positive environmental aspects of EVs and reduced maintenance costs didn’t wow them much either.
    Explaining how the Clarity will save them $1,000+ a year in fuel costs, and has a $7,500 tax credit wasn’t as much a wow factor as explaining how they can get the a brand new car with a 3 year warranty comparable to an Accord for only $14,500 ($30,000 - $7,500 - (8yrx$1,000). Figures different for your area of course.)

    Guess I’m not cut out to be a car sales person. Wait a minute, maybe I am...
    I’ve sold one more Clarity than all the sales persons combined at my local Honda dealer except one. So I’m the #2 Clarity sales person in Lexington KY! A sad bragging right.
    Louis Nisenbaum likes this.
  17. Tangible

    Tangible Active Member

    My own anecdotal experience is very different here in Massachusetts. Environmentalism seems to be the biggest driver of demand for electric cars and hybrids. PHEVs are, sadly, just as unpopular here as everywhere else.
  18. I suspect the local electric rates are the buzz kill, more than anything else.
  19. Tangible

    Tangible Active Member

    I don’t think so, because enthusiasm is very high for BEVs, with the main worry I hear being charging infrastructure. That said, our electric rates in New England are awful. But the antipathy to PHEVs seems to be based on ignorance among both the dealers and the potential customers.

    The people who are buying Tesla S, Audi e-Tron, Jaguar i-something, and soon Porsche Taycan and Mercedes EOQ for ~$100k shouldn’t be worrying about fuel prices, but they do. I always smile in the Costco parking lot when I see folks loading up their BMWs with bulk paper towels. Everyone likes to feel they’re getting a bargain.
  20. Clarity_Newbie

    Clarity_Newbie Active Member


    Fair enough. Without any discounts...over the course of one year...using raw numbers with no adjustment...the Clarity I drive actually returned 25.3 mi/kWh. One thing using the trip a or b for recharge calcs is the owner has to remember to subtract any miles generated when by the iCE when it comes on for "maintenance mode". Typically, the Clarity I drive runs ~5 to 7 miles each time it kicks on. So when I run the Clarity to 0 EV miles...the trip meter may read (summer) 62 or 70 depending on if the ice came on.

    Based on a year of data collection...I am comfortable using a 7% reduction for those unexpected ICE maintenance runs...hence the ~23 miles/kWh I used in the first post. The 7% reduction essentially equates to the ICE maintenance mode activating 35 times over the course of 1 year for ~210 miles.

    There are many ways to generate numbers (ie the old adage about statistics lie etc) For example...awhile back I drove the route that I know will return the greatest EV miles which I can easily generate 68 to 70. Based on 100% of the recharge kWh...utilizing 68 miles...I returned 4.51miles/kWh. That's saying something since I do live in the mountains and I lose 1.5 - 2 miles of EV the last mile up to the house everyday all day.

    Alternatively, I ran one EV 0 where I drove the interstate 22 miles instead of the usual 12 @65 mph...not surprisingly that had a negative effect on the m/kWh relative to the normal route...for that run. Again statistics can be generated however one wants the numbers to look.

    The numbers posted earlier are conservative estimates based on variables that work for me...in my climate...for my driving habits. I am very comfortable with the numbers posted as I know they are conservative...worst case as it were and that is the way I roll. Too often people use the best numbers that can be generated then act like they get that all the time. This isn't a contest...no bragging rights...wayyyy to many variables that influence numbers.

    From the numbers I have seen coming out of Southern California...I can't compete with them for about 8 months of the year, so I don't bother to compare. I'm sure the folks in North Dakota won't compare their numbers to those in warm climates during cold months either...and shouldn't.

    I only offered these numbers to help folks who have questions or are curious. The key take-away though is to only compare apples to apples from the same orchard. Its not a competition.

    Finally, driving habits are key to any numbers you read...some folks drive 35 mph all day with no interstate miles...others drive a combo...whatever. This fact will greatly influence "your numbers". Again...my numbers in the first post reflect a average dude, driving routine roads, 80% local/20% interstate, nothing special, not trying to achieve any certain level of efficiency. I run normal mode with a sedate driving style in mountainous terrain. Those numbers work for me.

    Methodology has to be consistent...based on data and used on a consistent basis and applied evenly. If that is done..even if the numbers are off a tish one way or the other..results are consistent and trends can be spotted. Some of the guess work would be unnecessary if Honda provided EV miles vs ICE..but alas...don't want to beat a dead horse.

    I pose a question to those who know...if the Clarity I drive was left in Econ mode...what percentage gain in efficiency can I expect to see? Versus normal mode? (Caveat...I rarely activate ICE in normal mode)
    Last edited: Aug 30, 2019
    Sandroad likes this.

Share This Page