darth_vad3r
Well-Known Sith
I pay 2.79 cents per kwh to charge overnight (time of use).
This is so ridiculous.
LOL, so true.
Approaching the point where if you are close enough, you should drive to @Knightshade ’s place to charge
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I pay 2.79 cents per kwh to charge overnight (time of use).
This is so ridiculous.
Yes, that is 0.7 cents/mi, not 7 cents/mi! For you, worrying about charging inefficiency and vampire drain really is completely unnecessary!
OP, in terms of sources of inaccuracy ...
1) Does your trip home end with any downhill stretches and/or large deceleration stretches shortly before stopping your car?
There can be several miles of added range from regen hidden from you which could translate to you not having used 46 miles off the dashboard. It seems like it’s possible that up to 1 kWh of regen may be hidden from the dashboard gauge’s distance number at any time. It’s not clear to me if this would stay hidden during a recharge event, I would presume not and it would be added back in as the charge progressed which would manifest as your efficiency for that charge session (as measured by increase dashboard range) being better than it actually was.
2) Also, using a trip meter gives better distance accuracy with 1 decimal place versus the odometer with rounded miles introducing as much as a full mile of error.
To quantify these errors:
1) 39 miles added to the range (204 -> 243) while charging is 9.555 kWh (39 mi x 245 Wh/mi). The 1 kWh max regen ‘error’ is up to 10% error here.
2) “39” off the odometer measured from OdoA (7958 +/- 0.5mi) minus (7919 +/- 0.5mi) = 39 +/- 1.0 mi. So that’s up to 2.56% error.
That all said, I agree with @AlanSubie4Life that something still seems off even with above sources of error:
Seems you charged at 240 V, 48 A so the efficiency should be quite high, easily in the 90’s.
8.4 kWh x 0.90 = 31 miles of added range for AWD with 245 Wh/mi internal charge rate constant. That’s 20% off your number of 39 added miles.
Something seems quite off with the numbers. I would repeat test again.
Also, doing it over a few days will capture vampire drain costs as well.
You really have to weight it for seasonality too since colder winter temps decrease the battery’s efficiency.
@OP. Not sure if your electric is under PG&E or not, and what rate plan you are on. Off peak for EVA is $0.13452 (summer) / 0.13778 (winter) per kWh, and $0.15633 per kWh for EV2. EVA was closed to new enrollment as of July 1, 2019, so if you are not in the plan then you can only enroll into EV2 plan.
Ultimately it's a small sample and prone to error, but these are the numbers I got.
The process was to charge the car to a specific range, drive it to work and back (that's the 39 miles) and measure the electricity consumption (from the grid) necessary to return the range to the pre-commute amount (I made a small adjustment because the range is never returned to the exact same amount). All that done, this was the result.
Could ignoring decimals have improved the outcome? Sure, or worsened it.
Is there a downhill portion? Yes, very short, but the segment is uphill coming back, naturally.
Could the reported grid usage be inaccurate? Also possible
Are you charging to 80%? 90% might be a better target for testing due to better accuracy in the voltage discharge/charge curve in the steeper sections of the curve (near higher and lower SoC, it’s flatter in the middle).
My charge seems to be within 1-2km (~ 1 mile on the display) when I charge to the same target. 250 start vs 243 end seems pretty large.
Yes, that’s what errors do! Given that your numbers seem to have a large error though, something might be missing or you got “lucky” and all the errors added up against you.
Regarding regen I was specifically curious if there was large regen near the end of the test, if it’s downhill to work and uphill back, that would lessen the chance of that specific thing being a possible factor.
Curious. How do you see this usage anyways?
Well, you need to divide by .83, or whatever charge efficiency your average is, to get wall kWh used.
This is assuming the Wh/mi number you mentioned is one pulled from the car’s trip meter (which is measuring DC kWh out of the battery, after losses from DC kWh into the battery, after losses from AC kWh in from the wall (or DC supercharging)).
So if you are trying to calculate a cost in kWh from AC, you should divide the DC kWh used according to the trip meter by anywhere from ~0.6 to ~0.9 (multiply by 1.11 to 1.67) depending on the AC power you charge at.
So saying the Model 3 should be better than your numbers quoted is missing the multiplier, so the final AC kWh cost might actually be higher than the numbers you quoted (~6-7c/mi) for an AWD 3.
My last daily driver cost around $0.23/mile in fuel alone at $3 a gallon, so I'll be saving roughly $2,500/year in gas savings. Adding maintenance, insurance, and depreciation savings on top is more like $4k/year in overall savings, maybe more. I don't keep anything long, but if I did the Tesla would pay for itself in savings alone eventually which is insane.
Quick computations say your former daily driver was getting 13 mpg and you were driving approximately 11K miles a year? Just think how much you would be saving if you were a traveling salesman or manufacturer's rep driving 25K a year or more?