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Driving efficiency Question

Discussion in 'Model S' started by tvguy710, Oct 10, 2019.

  1. tvguy710

    tvguy710 Member

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    I basically do the same drive to and from work every day. Give or take a mile or two depending on which way I go home. Been tracking it last 3 months on TeslaFi and just recently converted it into a spreadsheet. I am just curious, in the last 10 days, I have noticed two drives that have numbers that aren't on par with the rest. The only variable I can think of is that it was raining those days. Would that increase all the numbers just because of that? Everything else was honestly the same throughout, No AC/Heat, similar driving speeds throughout.

    Any ideas or thoughts would be great.
     

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  2. pgkevet

    pgkevet Member

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    The greatest factors to my usage are ambient temp at the start of a trip and how many times I have to brake/accelerate and battery state i.e the factors that interfer with regeneration and require battery heating.
     
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  3. David_Cary

    David_Cary Member

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    Yes - a wet road has a lot more rolling resistance.
     
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  4. tvguy710

    tvguy710 Member

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    Thanks!
     
  5. tvguy710

    tvguy710 Member

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    Thank you
     
  6. ewoodrick

    ewoodrick Active Member

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    And rain hitting the car slows it down.
     
  7. Chaserr

    Chaserr Active Member

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    Rain affects efficiency a lot, and snow even more. Your battery is dependent on thermal regulation to operate safely and efficiently, and the entire bottom of your car is the battery. All that water wicks away heat and your battery spends more energy warming itself back up again.

    This is on top of the normal every-car things that will reduce efficiency in rain.
     
  8. agtdDelirium

    agtdDelirium Member

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    Internal combustion vehicles are subject to the same physics that reduce efficiency due to wet or snow-covered roads, wind resistance, etc. The driver doesn't "see" those effects as much in lowered mpg due to ICE vehicles' extremely poor efficiency to begin with. Internal combustion engines are only about 20% efficient in converting gas to power at the wheels. Any road/driving condition that would require more power delivered to the wheel is largely masked by the poor efficiency of the ICE. You are adding a tiny fraction of inefficiency (road condition) to a hugely inefficient system to begin with. Effects on mpg are small and usually not noticed by the driver.

    Electric vehicles, on the other hand, are magnitudes more efficient in converting electricity to power at the wheels. Therefore small inefficiencies from road conditions are seen much more readily in increased energy usage.

    The only real benefit an ICE vehicle has over EV is cabin heating. All that inefficient heat loss in burning gasoline can be redirected into the cabin for comfort on cold days.
     
    • Informative x 1
  9. Oldschool496

    Oldschool496 Member

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    Wipers on constantly like you need here in Florida. Heavy use of power.

    First long trip coming back through a very familiar section of road knowing what I would need to get back home.
    Supercahrged, its telling me to stay longer then I know I need to get home. I leave anyway and two minutes down the road it starts raining hard for 2 hours. Wipers are going, defrost, you name it, I barely made it home.

    Moral is weather is definitely a killer and I swear to this day the system somehow knew the weather was going to get bad and told me to stay longer.
     
  10. ajdelange

    ajdelange Member

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    Rain - you betcha. Increases power consumption by at least a third in my experience.

    Some of the explanations here are entertaining. It doesn't actually have to be raining. A wet road surface is sufficient. The reason for this is that water has to be pushed out of the way and water is actually pretty thick stuff. Those of you with boats think about how many horsepower your boat engine develops to push you along at 30 - 40 mph and what happens as soon as you back off the throttle.
     
    • Helpful x 1
  11. mfel

    mfel Member

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    Yep, speaking from Pacific Northwest experience, water on roadway is the issue. It doesn't have to be much.

    Consider two things: if you are driving on dry pavement and hit standing puddle, you definitely feel the drag, right?
    Second, if we assume total tire width is about 1 meter, and the water depth is 1mm, then after only 1km your car has pushed aside or lifted and sprayed into the air 1 cubic meter of water. That is 1 metric ton. That takes a lot of energy.
     
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  12. Saghost

    Saghost Well-Known Member

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    Most ICE vehicles don’t give you anywhere near the detailed telematics - an obsessive that wrote down the trip computer results every trip might see the effects, but any other driver won’t unless they continue for the majority of the gas tank, whereas Tesla gives you trip by trip efficiency and exposes it in the API where it can be collected and collated easily.
     
  13. Bmac

    Bmac Member

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    But you do have to be careful of the numbers from TeslaFi. in fact, they ask that you reply to their email messages with the actual watt hours per mile registered on your drive from your dash so they can better calibrate their algorithm. I don't know if that difference from actual "Tesla reported" to "TeslaFi" reported results would have a bearing on weather and temperature variables.
     
  14. Hugh Mannity

    Hugh Mannity Mediocre Member

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    I don't think the wiper motor running has much affect; I have no idea how many watts the motor uses but I suspect that the Tesla battery pack could run a wiper motor for weeks possibly months !!

    The degradation is mostly due to the friction of tyres in the wet ;)
     
  15. tvguy710

    tvguy710 Member

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    Thanks I actually spent last 2 months watching the screen vs teslafi and there is an option in the settings for offset for my vehicle. Once finding that offset it’s been pretty solid, very close!

    Just wanted to gauge this for my self nothing else.

    besides the charging at my house to see how may more Solar Panels I need as well but that’s pretty straight forward.
     
  16. drklain

    drklain Member

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    It's the wet roads. Don't believe the theories about the rainwater cooling the battery or the load from your windshield washers. The windshield washers exert minimal power usage on the car (like the LED lights) and are in the noise compared to other factors. Battery heater is a huge electricity user but I have NEVER seen rain/water splashing on the battery have that kind of thermal effect. Outside air temperature is what affects the battery temp.

    The issue IS the wet roads and the increased rolling resistance to the tires. From a physics point of view, on a dry road your tire rolls as designed. On a wet road, the tire pushes the water out of the way (to either side or into the grooves in your tire tread). It doesn't seem like that would be much resistance, but it is. This has nothing to do with electric cars. ICE and hybrids have the same issue and show increased fuel consumption when driving on wet roads (lower mpg). Race cars see it very clearly although there are other factors there (they drive at slower speeds and the engines are designed for optimum efficiency at dry track race speeds). Driving on wet roads can decrease your efficiency by as much as 10%, but it is hugely variable depending on the road surface, amount of water, etc., so it is hard to predict how much a given condition will affect you. What you can rely on is that your Wh/mile number will go up when you are driving in rain.
     

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