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Discussion Starter #1
With my last couple of ICE cars I've kept a log of tank-to-tank mpg as a way of measuring actual fuel consumption (the on-board estimates usually proved to be over-optimistic). I've been trying to do something similar with my Model S70 RWD which has done a modest 1780 miles over 3 months (around the UK average I think).

I've estimated an average of 489 Wh/mi over 1272 logged miles, while my Trip A records 363 Wh/mi over 1760 miles. The difference is due to a combination of charging efficiency and battery losses when the car is off. I don't know if others have posted similar data but I'm just reporting it here as an example of real-world energy cost per mile.

Using a bag of assumptions I calculate that to date the fuel cost/100 miles is £4.90, versus about £10 for my old 50 mpg Prius. The real-world figure is a bit disappointing based on running cost guestimates I made before I ordered the car, but not completely unexpected (I was hoping for more like £2.50-£3.00 per 100 miles). I'm still perfectly happy with the range and performance, the cost/mile was never a key factor for me. It would be much more favourable if I did a significant amount of mileage using superchargers or free public points but that's not the case for me day-to-day.

Some further notes for anyone interested
- the vast majority of charging is at home, where I've calculated the 32A supply is typically 94% efficient
- the car does a short urban commute, so most of the losses are due to battery charge depletion when the car is parked and switched off. A higher mileage car wouldn't suffer so much from this issue.
- "Always Connected" is off - the car often needs to boot up before I set off. I've estimated it loses the equivalent of about 5 typical miles / 24 hrs in this state.
 

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What is your kW tariff at home? I have Economy 7 tariff ( 6p/kW) and I can easily do £3 / 100 miles. Lately, with the warm weather, I really get good Wh/mile like 280-290 Wh/mile on long trips and 320-330 Wh/mile city driving, Range mode off, Always Connected on. I have a 90D, 10k in 6 months.
 

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Can you let us know how you have taken these measurements? Presumably there is some sort of 'out-of-the-wall-socket' type meter in the loop somewhere? The accuracy of that is quite significant!
 

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Discussion Starter #4
@VirtualM my electricity tariff is 10p/unit all day - if you're getting about £3/100 miles that scales up to £5/100 miles for my tariff so it looks like we're in the same ballpark. I recently checked a couple of E7 tariffs and it looked like the more expensive day rate outweighs the night rate for my usage patterns but admittedly I haven't done an exhaustive search (since getting the car about 40% of my usage is at night with charging + other overnight stuff).
 

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@VirtualM my electricity tariff is 10p/unit all day - if you're getting about £3/100 miles that scales up to £5/100 miles for my tariff so it looks like we're in the same ballpark. I recently checked a couple of E7 tariffs and it looked like the more expensive day rate outweighs the night rate for my usage patterns but admittedly I haven't done an exhaustive search (since getting the car about 40% of my usage is at night with charging + other overnight stuff).
Typically you need at least 45% of usage to be in the offpeak period before E7 starts to pay, and for it to be a clear win you'd want more than half.

The difference is due to a combination of charging efficiency and battery losses when the car is off.
And cabin preheating.
 

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Discussion Starter #6
Can you let us know how you have taken these measurements? Presumably there is some sort of 'out-of-the-wall-socket' type meter in the loop somewhere? The accuracy of that is quite significant!
Agreed re: accuracy - my charging supply is a dumb commando socket without any dedicated metering so I've been using the TeslaLog website which logs the car's own records of input supply voltage and current every minute during a charging session. This is where I got my 94% figure from (and to be honest I'm quite pleased with 94%).

Before that I'd tried using a simple GeoMinim clip-on monitor but it was hopeless, presumably because the output voltage drops when the car is charging but the GeoMinim has a crude calibration factor assumes a constant supply voltage. The TeslaLog measurements do seem to tally with the electricity meter (after guestimating the underlying overnight house usage and subtract it from the meter reading).
 

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Discussion Starter #8
And cabin preheating.
Yes I used the term "battery losses" which is a bit unfair, it's presumably more to do with the car running background systems, keeping everything at a suitable ambient temperature, preheating, etc.

I used TeslaLog for a few weeks, noticed the increased standby drain, and now switch toggles on the homepage to hopefully reduce the standby usage except when charging when I like to monitor the electricity supplied. It could be that even with the toggles off the standby drain is elevated but TeslaLog isn't now actively logging anything except when switched on for charging sessions.
 

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I've estimated an average of 489 Wh/mi over 1272 logged miles, while my Trip A records 363 Wh/mi over 1760 miles. The difference is due to a combination of charging efficiency and battery losses when the car is off. I don't know if others have posted similar data but I'm just reporting it here as an example of real-world energy cost per mile.

Using a bag of assumptions I calculate that to date the fuel cost/100 miles is £4.90, versus about £10 for my old 50 mpg Prius.
If that's based on last 3-4 month than the next 3-4 should be much better with warm weather. Even my Leaf needs 300-350 Wh/mi to keep going on short trips in winter.

Also bear in mind the performance of the Model S is more 535i than a Prius. My old 335i would struggle to hit 25mpg on urban trips. Tank range on £70 of petrol was often no more than 250 miles.
 

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Typically you need at least 45% of usage to be in the offpeak period before E7 starts to pay, and for it to be a clear win you'd want more than half.
.
This prompted me to check my usage pattern and I'm using only 30% E7 and it's still cheaper than not. Not by much though.

I'm with Scottish Power in area 19 and the E7 rate is currently between 22.30- 00.30 & 02.30-07.30.

Does the Tesla charging app enable start/pause/start/stop?


Sent from my iPhone using Tapatalk
 

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You can sense the frustration in that reply ;) The only option for scheduled charging is to set a start time and charge limit in the car. You can't even set a finish time, just manually end charging from the app. Useless for a split E7 time band :(
 

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You can sense the frustration in that reply ;) The only option for scheduled charging is to set a start time and charge limit in the car. You can't even set a finish time, just manually end charging from the app. Useless for a split E7 time band :(
That does seem to be an extraordinary shortcoming. The car can do all sorts of wonderful things but setting a stop time for charging isn't one of them o_O
 

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I didn't know there was such a thing as split E7. What's the logic (if any!) behind it?
The peak and offpeak hours are set by each DNO (regional operator). I wasn't aware of anywhere where E7 was split like that, but E10 tariffs (where offered) are usually split into 3. Where I am E10 is 13-16, 22-00 and 02-07 I think.
 

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The only option for scheduled charging is to set a start time and charge limit in the car. You can't even set a finish time, just manually end charging from the app. Useless for a split E7 time band :(
My 70D gains exactly 10% SOC per hour from my 32A Commando socket, so the maths isn't difficult.
 

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My 70D gains exactly 10% SOC per hour from my 32A Commando socket, so the maths isn't difficult.
Agreed, but the point is you can't stop charging at a specific time, which on an economy 7 tariff that stops at 00:30 and doesn't start again until 02:30 is less than helpful.
 

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With your split tariff system you would need to be able to program two charging sessions (two starts, two stops) per night and no car will do that. But it really isn't difficult to work out when the car will reach X% SOC and set the charge limit accordingly.
 
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