Something to Think About

Discussion in 'Clarity' started by David Towle, Jan 10, 2019.

  1. David Towle

    David Towle Active Member

    We all think our Claritys get great gas mileage, right? They get about 40 mpg, meaning they burn about 3 oz of gas in a minute to go 1 mile. However that same amount of energy powers our bodies typically for 480 times as long, about 8 hours. (1 kcal = about 4 BTUs) Think of all the stuff we can do in 8 hours, walking, carrying, dancing, working, cooking. (Yes we have only 1 fuel in common, ethanol, but calories are calories)

    The question becomes why must even these efficient vehicles suck up so much fuel, when they weigh only 25 times as much as us and have the advantage of a very smooth wheel based propulsion system versus our rickety legs?

    I want to be a good custodian of the environment, so until we figure out how to do REAL automotive efficiency I leave the car at home and walk or ride a bike whenever possible.
  2. tim

    tim Member

    I think in terms of the work that I want to get done. I could stay home and not do any work, which would be the greatest energy savings, but that's not my goal. I could walk or bike to work, but I would rather spend the commute time doing something else, like eating dinner with my family at an early hour. I also find the relative safety of a car compared to a bike to be worth the energy and money expenditure.

    But everyone needs have their own goals and priorities, so to each his own.
    02Duck likes this.
  3. KentuckyKen

    KentuckyKen Well-Known Member

    I think I we have already figured out the efficiency and environmental solution to personal travel by automobile. It’s EV and solar.

    My Clarity is powered by solar on my roof for 90%+ of its miles so I’m virtually as efficient and non polluting as if I were walking or biking around (which at my age and disability can’t be done for any trips over a quarter mile). So I’ll match carbon footprints with you any day of the week.

    [And yes I know you have to also figure in total life cycle and cradle to grave manufacturing, sourcing of materials, and recycling/disposal, etc.]
  4. David Towle

    David Towle Active Member

    I'm mostly solar too. Solar does cut the number of calories consumed about in half compared to gasoline or fossil electricity, but its still a lot.

    I guess my main point with the post is it seems like there must be a lot of efficiency improvements we have yet to discover.
  5. insightman

    insightman Well-Known Member

    Efficiency, speed, comfort -- pick any two.
    K8QM likes this.
  6. Fast Eddie B

    Fast Eddie B Active Member

    1) I think the answer is SPEED. How much “fuel” would it take to propel us 65 mph, let’s say. Wind resistance increases as the square of the increase in velocity. How about if we weighed 4,000 lbs and could carry 5 adults.

    2) Our “rickety legs”, and the energy systems used to propel them, are the results of billions of years of evolution. One would expect them to be marvelously energy efficient, and they are. Bipedal locomotion, where we’re constantly “falling” forward from one leg to the other, may seem rickety but is really quite ingenious.
  7. neal adkins

    neal adkins Active Member

    Remember the clarity is rated 110mpge. Another way to look at it is how many calories would you burn to walk 40 miles. At 1 mile every 15 minutes thats 10 hours of time. So energy is not the only concern. The average person burns about 110 calories per mile. Thats my argument against exercise. Its not efficient
    Last edited: Jan 12, 2019
    David Towle likes this.
  8. Walt R

    Walt R New Member

    As Fast Eddie B says, I place most of the difference on speed. Using his argument in reverse, since PHEV/BEV don't have the losses from idling, I'll bet that if you drove your Clarity at 3.5 mph on flat ground you'd reduce that ~500x energy ratio to something like 5x. After all, 70/3.5 = 20 and 20x20 = 400 so for the wind resistance portion, you've got 400 times the energy lost (static losses will be a smaller ratio).

    (This is related to a post I haven't made yet, about a mile is not always the same as relates to the EV Range estimate. Getting off the highway at 60 and driving 35 mph, you will get two miles for each mile lost on the meter. Driving 25 or below is almost free, relatively speaking.)

    Interestingly enough, when I have compared the published estimates for calories burned per hour for human activity (walking, cycling) to the actual energy needed for the activity from physics, I find humans around 15-20% efficient at converting calories to work, which is the same range that conventional gasoline vehicles achieve (a gallon of gas has over 120 MJ of potential energy, but this results in around 20-24 MJ at the wheels).
    MNSteve and David Towle like this.
  9. MikeB

    MikeB Member

    Natural selection beats engineering every time.
    David Towle likes this.
  10. neal adkins

    neal adkins Active Member

    I think you nailed it. We are just spoiled when mostly using ev mode and then only getting about 40mpg in hv mode. I liked the point you made about how the car can carry 5 adults and cargo and still get 40 mpg....big difference. Im not trying to save the world but i like the idea of less pollution and less energy wasted.
    02Duck likes this.

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