The result was upside down from what I would have thought!!!

Discussion in 'General' started by Geor99, Nov 16, 2018.

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  1. Geor99

    Geor99 Active Member

    I ran some calculations that really surprised me. I recently bought a Honda Clarity. It's rated to get 47 miles on a charge, which is roughly 19kwhr , accounting for charging efficiency.

    It also claims to get 42mpg with a completely drained battery in "HV" mode.

    Electricity rates in San Diego average 23cents/kWh . To make it simple, if I charge the battery 89% or 17kwhr, it will travel the same distance that a gallon of gas would, 42 miles.

    So at 23 cents, that's $3.91 using electricity. Gas here is $3.85. So I'm calculating that's it's actually CHEAPER to fill the tank than plug in.

    Yes, the utility does have some complicated off-peak discounts for ev owners and many people have free charging at work, like me, but this stat still completely amazed me.

    At the common average rate for power in SD, it's cheaper to run the car on gas- even though we pay $3.85 / gallon out here !!!!

    Amazing, no??
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  3. rickyrsx

    rickyrsx Active Member

    23 cents/kWh? Dang that's expensive!

    Sent from my iPhone using Inside EVs
  4. bwilson4web

    bwilson4web Well-Known Member Subscriber

    Actually it does make sense. In Huntsville AL, we pay $0.10/kWh and yesterday I topped off the 2014 BMW i3-REx with Costco premium, $2.60/gal. Using EPA specs which are fairly accurate:
    • $2.90 for 100 mi EV
    • $6.76 for 100 mi gas
    Since your electricity rate is nearly twice what I pay, it makes sense there would be EV-gas parity. With time of day rates, it would be sensible to get the cheapest, midnight rate.

    This summer it was so hot that I used time of day charging to start at 11:00 PM to 9:00 AM. This minimize the heat load on the car battery. If I charged during the heat of the day, the cars would turn on their A/C trying to keep the battery cool.

    Bob Wilson
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  5. DaleL

    DaleL Active Member

    First, the Clarity does not utilize the entire capacity of the 17 kwh battery. It has about 14.4 kwh available for the 47 mile EV range. The correct calculation is (42/47 x 14.4 kwh x 90% charge efficiency = 16 kwh x .23 = $3.68. So although it is close, it is cheaper to charge.

    Here in Florida, I last filled up at $2.45 per gallon and electricity is 11 cents per kwh. However, you make a good point. A highly efficient hybrid such as the Camry 46 mpg, Accord 47 mpg, or Insight can actually approach the cost per mile of an electric vehicle. The EPA rates the Clarity as taking 31 kwh per 100 miles and the Tesla 3 as taking 27 kwh per 100 miles. So in your situation a Tesla 3 should cost $2.87 for that 42 mile trip and a Honda Insight (non-touring 51 mpg) should cost $3.17. The Tesla electric vehicle wins, but not by a large margin. However, the Clarity loses, but also not by a large margin.
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  6. ClarityDoc

    ClarityDoc Active Member

    Are you also considering (~20%) losses during charging?

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  8. DaleL

    DaleL Active Member

  9. Geor99

    Geor99 Active Member

    Some have disputed my electricity rate, which I got here from google: As of February, SDG&E's average residential rate for electricity was 21.1 cents per kilowatt hour, and is expected to rise beyond 23.3 centsthis summer.

    My point is that it wasn't the blowout that I assumed. "Free" at work helps me, though. I also have solar, which helps as well.
  10. Geor99

    Geor99 Active Member

    I'd be interested to know the calcs from different parts of the country.

    I have a house across the border in Mexico where gas is a whopping $4.21 (21 pesos per liter for 87 , at 18.5 pesos per $ & 3.79 liters/gallon.)

    Power is between 6cents and 22 cents depending on amount used. Daily charging would result in losing all subsidies and result in 22 cents/kwhr. This would still beat $4.21 gas. However they don't use 10% ethanol, so it gets better mileage.

    Bottom line gets too complicated:)
  11. Mark Miller

    Mark Miller New Member

    I am more interested in minimizing my carbon footprint, and in that comparison, with my Prius Prime and using Consumers Energy in Michigan, we have:
    Prime EV 25 kWh / 100 miles * 1.24 lb CO2 / kWh / 0.88 (measured) = 35 lb CO2 / 100 miles EV
    HV 1.85 gal / 100 miles * 19.59 lb CO2 /gal = 36 lb CO2 / 100 miles HV
    (54 mpg = 1.85 gal/100 miles)

    ...nearly a tie, 35 lb CO2 / 100 miles vs. 36.
    Notice I am using 88% charging efficiency, average of many measurements with my set-up.

    If I calculate dollars instead, it comes to $3.69/100 miles EV, $4.63/100 miles HV, assuming $0.13/kWh and $2.50/gal gas.
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  13. 101101

    101101 Well-Known Member

    Intent of this thread seems to be to push the idea that gas is competitive on cost with electric. This is a face value bogus argument, its been debunked countless times. Gas is not competitive with electric and there is no way to skew things to make it seem like it is. Hybrids are obsolete even the phev sort. ARAMCo is doing a moon shot program to try to keep ICE around but even if it succeeded in its goal of more a ICE, fossil fuels are simply politically and economically unacceptable. Fossil fuels were always a lean cannibalistic proposition but 70 years ago their primary utility as a fuel ceased and their reason for existence began to be control. No one who can think wants to be subject to that tyrannical control or its pollution. Also the Clarity was sadly converted by Honda into a weird mobile so its not basis to make comparisons on. And as above you don't compare the Model 3 to an Insight, Insight is a smaller vehicle. Not sure you can even call Model 3 a compact car (don't think despite VW thinking it can take on Tesla with Bolt like compacts) and Insight if I am not mistaken has been a sub compact and although larger now may still be sub compact. Might as well be comparing a Toyota Yaris and a Model X.
  14. Geor99

    Geor99 Active Member

    I'm not trying to push any ideas. I'm simply stating that I was surprised that the numbers were so close. I thought that my clarity would be far less expensive to plug in rather than gas up.

    The numbers show the difference to be minimal.

    However, give me 10k in government money, free charging at work, HOV access for 4 years, and somewhere to put my excess solar power; and I'm in:)
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  15. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    It is amazing just how much the cost for a kWh of electricity varies across the country.

    According to the EIA (U.S. Energy Information Administration), as of January 2018, State average electricity rates varied from a low of 8.13¢/kWh, in Arkansas, to 23.87¢, for Hawaii. Second highest is Alaska, at 17.93¢.

    But that doesn't tell the whole story. Some localities have local rates that can add a lot to the State rate. It's been reported by several people that certain areas of New York have electricity rates around 35¢ per kWh! Altho I'm not sure that is a year-round rate; that may be only with a summer surcharge.
    Last edited: Nov 16, 2018
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  16. interestedinEV

    interestedinEV Well-Known Member

    Pun intended in this statement (yes Grammar Nazi :)), "your mileage varies". The price of gas and the price of electricity differ from area to area (not just state to state) and there can be wide variances. Complicating all of this time of day pricing and all other gimmicks that utilities have learned from cell phone companies. So I am not surprised that in some areas it may be cheaper to use a ICE instead of PHEV. Now with a pure BEV, I am going to believe that it will be better (Tesla shows savings with a lower gas price). PHEV's with small battery range (let us say 50 miles) do the not have the efficiency of a larger battery pack. So I would not personally not recommend a PHEV if you are purely looking at it from cost savings, but for those who want to do something for the environment but do not want to pay a big premium for that. If you want significant operational cost savings, look at PHEV with a larger range or a BEV.
  17. Geor99

    Geor99 Active Member

    I'm not trying to be argumentative, I just want to learn.

    That being said, my clarity has roughly a 50 mile range. I've driven it 1200 miles and pretty much never used gas, outside of just playing with the buttons:)

    Anyway, I can charge at home and at work. How would a bigger battery with a longer range help my math, since I have not run out of juice yet?

    Do you get more miles per kWh with a bigger battery? You mentioned a greater efficiency with a bigger battery. Do you mean that a bigger battery can go a further distance on a kWh of charge than my 17kwr battery? If so, how much further per kwh?

    Please help me to understand what you meant. Isn't a bigger battery just more smaller cells put in a string?

    Once again, I'm looking to learn not argue.

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  18. bwilson4web

    bwilson4web Well-Known Member Subscriber

    Your battery is matched to your usual commute. A larger battery doesn't help.
    No, in fact the larger, heavier battery increases the rolling drag and inertial losses. But you can calculate 50 miles/17 kWh ~= 2.9 mi/kWh. I have a BMW i3-REx, 72 miles / 18 kWh ~= 4 mi/kWh. My BMW has a carbon fiber body on an aluminum frame.
    Normally in parallel 'bricks' for capacity, these bricks are put in series for the fixed voltage for the controller and motor. Tesla uses smaller cells, 18500 for Model S/X and 2170 for the Model 3. This modular approach allows the same Tesla to come with different sized battery packs. In contrast, the other manufactures are using much larger pouch or prismatic cells so variable sized, traction battery packs are impractical.

    Bob Wilson
    Last edited: Nov 17, 2018
  19. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    It looks to me like you are referring to this comment above:

    Actually, a PHEV with 47-50 miles of EPA rated range puts it near the top of the available PHEVs. PHEVs with a considerably smaller range, 25 miles or even less, are all too common.

    For a BEV, larger battery packs have many advantages. Not only longer range on a single charge, but the ability to charge faster (on the basis of miles added per minute of charge). Larger battery packs also will retain their capacity over time better, allow greater flexibility in driving in very cold weather (that is, when the BEV's range drops due to very cold weather, it may still have sufficient range to get where you want to go), and retains better resale value because it won't have lost as much capacity over the years.

    However, for PHEVs, the situation is different. PHEVs, at least the well-engineered ones (most notably the Volt), are built with more reserve capacity in the battery pack, so may not lose as much (or not any) usable capacity over time. Furthermore, the very fact that PHEVs can continue to run, using gasoline, when the battery is near-exhausted, may encourage drivers to use more of the available battery capacity.

    Geor99, so long as you never drive past your Honda Clarity PHEV's all-electric range, then the advantages of a larger battery pack may not apply to you; not to your specific case. I don't want to put words in the mouth of InterestedinEV, but perhaps he was referring to average energy efficiency for everyone driving a particular model of PHEV.

    As Bob Wilson pointed out, a larger battery pack does not add to energy efficiency. As he also correctly pointed out, if all else is equal (it never is in anything as complex as an automobile, but let's pretend for the sake of argument) then a heavier battery pack would actually result in slightly lower efficiency due to greater weight, which adds to both inertia and rolling resistance.

  20. DaleL

    DaleL Active Member

    The EPA passenger/luggage volumes for: Tesla 3 = 97/17; Honda Insight = 98/15; Honda Clarity phev = 102/15; Honda Accord hybrid = 106/17. The Tesla 3 has the LEAST passenger volume of these cars.

    The latest automotive engines, such as in the Clarity, achieve close to 40% thermal efficiency. Fixed fossil fuel power plants are not much more efficient. The argument for phev and bv is not cost (mpg etc.). Instead it is the driving experience. There is that instant smooth power, instant cabin heat, and (depending on the source of electricity) a reduction in pollution.
  21. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    A couple of reality checks:

    1. Some of the small ICEngines found in modern automobiles may be able to achieve as high as 38.5% maximum thermal energy efficiency -- which means efficiency as measured in a bench test run at a its most efficient, stready RPM speed -- but certainly not an average thermal efficiency that high in real-world driving conditions, when most of the time the engine is not run at its most efficient speed. In real-world conditions, ICEVs are lucky to achieve 15-22% energy efficiency, altho that includes mechanical drivetrain losses, not just the inefficiency of the ICE as a heat engine. PHEVs can achieve somewhat higher efficiency when using the EV drivetrain to boost the efficiency of the ICE powertrain, but certainly not an average of 40% thermal efficiency (as measured by burning gasoline to push the car down the road, and not including electrical energy drawn from a wall plug) in real-world driving conditions.

    2. Large marine (ships') diesel engines can achieve as high as ~51% thermal efficiency. That's actual measured efficiency, not just theoretical efficiency. They achieve advantages both from larger engine size resulting in less heat loss, and from the fact that ships can run their engines for long periods at constant speed... unlike driving in real-world traffic.
    Last edited: Nov 18, 2018
  22. Geor99

    Geor99 Active Member

    Thanks, that was helpful. I was recently discussing my PHEV with a friend. He brought up an interest point how airlines often hedge the price of fuels.

    In a way, a PHEV is similar. If gas plunges to a very low price, users can gas up their vehicles. If gas remains high, they can continue to plug it in.

    Then we got to thinking: what will happen to the prices of both gas and electricity when a large % of people go electric?
    Before this car, I purchased roughly 900 gallons of gasoline per year. I'm going to buy under 50 going forward, if all goes to plan.

    If millions do this as well, the price of gas could plummet, whereas electricity could rise.

    A PHEV is kind of a hedge against this. From an economic standpoint, we can toggle to whichever is cheaper each week.
    Does the Clarity have this same Volt battery characteristic?:

    "However, for PHEVs, the situation is different. PHEVs, at least the well-engineered ones (most notably the Volt), are built with more reserve capacity in the battery pack, so may not lose as much (or not any) usable capacity over time. "
    Domenick likes this.
  23. bwilson4web

    bwilson4web Well-Known Member Subscriber

    Our PHEVs are the ultimate flex-fuel vehicle.

    Bob Wilson

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