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Discussion Starter · #1 ·
In case anyone would be interested, i thought I'd share some data on driving with my bike on the roof. (Large enduro type mountain bike, fork mounted).
Highway speeds up to 95 mph, I've been getting 44-48 kwh/100 average over 100 mile trips. Generally flat roads on front range Colorado. Low 90s efficiency score. 60s temp.


Tire Wheel Land vehicle Car Vehicle
 

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2 weekends ago.65 to 75 degrees F. Fully charged when left.45mph(30%) to 65mph(60%)(other 10%)mph speeds. My bike 2004 Intense Spider on straight trailer hitch (no rise in hitch adapter, bike is lower than the top of the car). 80 miles to race. 80 miles back. 61 miles left on guessometer. It appears that the car doesn't know it is back there.
My actual mileage seldom goes over 2 mi/kw when using my metered charger supply, compared to car's odometer. I take monthly readings on the two.
 

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Discussion Starter · #5 ·
So, are you getting 50 kwh/100 regularly? I was pretty pleased for driving at such high speeds to be in the 2 2 miles per kw average for 200 miles when i was driving at 75-95 highway speeds with the bike. I do much better without it.
 

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I measure my usage by the meter that feeds my charger, that charges the battery, not by the cars inference of how much it is using out of the battery. There is heat that is lost when charging. I was getting 2.6mi/kw on my 160mile trip out of the battery.
 

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The car's calculation is actually spot-on, if you have a healty battery: the mi/kWh figure per trip in the "Journeys" list on the JLR website (or the apps) is accurate.
Not sure I 100% agree with that. For individual trips I would agree. However, I recently went back through my journey history for 2 1/2yrs to see if any battery degradation could be seen. End result, after multiplying miles by efficiency for each trip and summing between charges, the energy used and the corresponding drop in battery % was not consistent. Using those numbers to calculate a full battery charge led to numbers between 84kWh and 72kWh with no clear pattern. My charging data (posted previously) was far more consistent.

I feel these numbers may be effected by "lost journeys" occasionally, but there seem to be other issues at play.
 

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Ok that's interesting but this thread is about individual trip efficiency calculation, hence my comment, and you say you agree with that.
I wouldn't use trip efficiency to calculate battery degradation either ...
 

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I measure my usage by the meter that feeds my charger, that charges the battery, not by the cars inference of how much it is using out of the battery. There is heat that is lost when charging. I was getting 2.6mi/kw on my 160mile trip out of the battery.
I've been logging most of the car's consumption as well. I reset the trip odometer when I charge, note the mileage, GOM before and after as well as the efficiency of the last session. That gives me data on mileage for a session, ∆SOC, ∆GOM and efficiency. I use the efficiency and ∆SOC to extrapolate an estimated battery capacity, millage and ∆SOC to estimate the range and compare the ∆GOM and mileage to see how good the GOM actually was. The estimated battery capacity is all over the map as you noted. I definitely think it does not account for batery efficiency so instead of a the real physical battery capacity, we are actually seeing what the battery capacity is under those specific conditions (temp etc...) vs. the theoretical capacity at some reference conditions. For example, if it is cold, the capacity of the battery to hold electrons is not any different. The ability to push out electrons might be different so there is a apparent capacity, which can vary quite a lot and efficiency vs. ∆SOC might not capture that.
 

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Ok that's interesting but this thread is about individual trip efficiency calculation, hence my comment, and you say you agree with that.
I wouldn't use trip efficiency to calculate battery degradation either ...
No offense meant, but the problem is that if the individual journey efficiency data is "spot on", then summing them between charges should be similarly accurate. If it is not legit to add across different journeys on different days under different driving conditions and weather, then it is not legit to compare the journey efficiency from one journey to another. Thus, the numbers are real, but are meaningless without comparing to other numbers.

This thread IS about efficiency on individual trips, but if we don't have a reference point, then the number is just a number.
 

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Absolutely no offense taken! (Or meant ;) )

My reference points are the OBD readings, which match exactly the trip reports. What does happen though is that the battery SoC (in kWh, as reported by OBD) can change overnight, definitely due to overall "pack temperature" and probably also due to cell imbalancing (also probably temperature, in this case temperature heterogeneity within the pack). And then there are idle times between trips and other non-trip consumers. So adding up trips will likely give inconsistent estimates.

And then there's some "overshoot" at 100% charge, where both OBD and WattCat report more kWh in the battery at the end of charging than a few hours later, somewhat (though not totally) independent of battery temp.

But yeah, the entire question of range and efficiency with or without rack is totally confounded by outside conditions and the usual stuff we all know about ...
 

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In reference to efficiency: I have heard it said a gas car only uses about 1/3rd the gas's available energy, to power the car down the road. Since we are trying to use our battery and comparing it to energy used just to power the car down the road, shouldn't a gas car be able to minus 2/3rds of the gallons of gas it has used when driving down the road, to come to a MPG figure to calculate energy efficiency? The government has decided not to include our charging's heat loses, in the battery, charger & wiring, in their calculations and the electric car manufactures have followed that standard. Just a thought!
 

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Correct, the remainder is lost as heat during the process of running the engine. That heat is lost except for the small percentage used to keep you warm in the winter. Thus, an ICE is very inefficient. By comparison ~10-20% of the energy is lost in charging the battery.

Using the content of the battery as the basis vs the content of the fuel tank seems consistent. But, to be fair we really should consider the whole process from drilling or generation through to filling the battery/tank. That said, efficiency really is not the driver of EV's, less pollution and cleaner air is the issue.
 

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This. As long as renewables are a smallish share of electricity generation, EVs are not as great as one might think wrt total energy efficiency.
Efficiency is a good measure of the use of a battery of charge, or a tank of gas, but generating efficiency is not really relevant. How much of the incident radition do solar panels covert to electricity? How much of the air movement (wind) is converted to electricity? How much of the biomass of a prehistoric tree gets coverted to crude oil, and subsequently extracted and refined?

This thread started questioning efficiency of the I-Pace under different conditions. That's where the efficiency discussion should stay.
 
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