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kWh used

Discussion in 'North America' started by TTT, Apr 14, 2015.

  1. TTT

    TTT Member

    Jul 10, 2014
    San Diego
    I've been trying to calculate whether using Uber to get to and from a Tesla SCtr to the hotel is more cost effective vs paying for Chargepoint at the hotel, but I'm a little confused on the amount of kWh used between charges. If I charge to 100% and started at 60%, does this mean I used 34 kWh of the 85 kWh battery? If so, then why does the dash show Total Energy Used since last charge to be only 28.7 kWh?
  2. Robert.Boston

    Robert.Boston Model S VIN P01536

    Oct 7, 2011
    Portland, Maine, USA
    I don't entirely trust that "Total Energy Used" figure, as I think it doesn't count power consumption while parked. But there are two effects that work in opposite directions: first, although the battery is nominally 85 kWh, the "visible" portion is less. How much less is a matter of debate, but at least 5% of the battery capacity is hidden. In round numbers, assume you have 80 kWh of charge to go from 0 to 100% SOC. Second is losses. Chargepoint charges you for power it sends to the car, and some of that power is lost in the process of storing it into the battery. Others will have hard data, but I think the charging losses are about 10%, e.g. you'll use ~90 kWh to put 80 kWh into the battery.

    To my way of thinking, the convenience of simply charging at the hotel would outweigh any small cash savings of charging at the SCtr.
  3. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

    Jun 21, 2012
    As Robert noted, "kWh used" doesn't count power consumption if the car isn't moving ("P" or "N") or during pre-conditioning, and I suspect the same is true when in D or R at 0 mph, because waiting at a red light with the heat running full blast doesn't generate a higher energy use curve than stopping for a few seconds. I would not rely upon the "kWh used" - I'd probably use % SOC as an indicator if you really want to do the calculation.

    And as Robert says, include overhead of ~10%.

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