REAL efficiency and electricity costs

Cliff Hannel · Apr 18, 2013

First: love the car - this is not intended to indicate it is anything but a game-changer (I posted compiled shipment numbers showing how game-changing here), the watt-hours-per-mile indicator in the car does NOT really tell you how much electricity you will need from your grid/solar connection.

I ran calculations that take into account both charger efficiency and vampire (parked) energy use and came up with numbers more like 75% overall efficiency. I've included a snapshot of the calculations below and you can download the Excel spreadsheet from http://EVTripPlanner.com/TeslaOperations.xlsx (has a lot of other stuff, too).

Tommy · Apr 18, 2013

Your End-to-end efficiency (energy used driving/energy from wall) of approx. 70% do not match my real world numbers. I have monthly data points: the actual energy used driving is derived from Tesla's dash display; the energy from wall is derived from a watt meter monitoring the wire feeds to the dedicated EV outlet.

Here are my data points:

Month Odometer kWh Wall Meter kWh Charging Efficiency

December 707.0 813.0 86.96%
January 896.8 992.0 90.40%
February 1148.9 1371.3 83.78%
March 1348.7 1163.2 86.25%

Note the month of January's efficiency. It is about 5% higher than the other months. That is because sleep mode was enabled on the car and the 5% gain fits with what Elon mentioned was the aprox. loss due to vampire drain.

Also note that the charging efficiency I recorded also fits with the "up to 92%" charging efficiency Tesla has posted in the spec sheet for the S if sleep mode where enabled.

Sorry for the formatting, the post doesn't reflect how it is shown in the editor

Cliff Hannel · Apr 18, 2013

@Tommy - thanks for the data. Note that March kWh numbers are probably reversed, as somehow the Wall kWh was less than the Odo kWh! As long as the time periods align and the wall meter measures as expected, this should be accurate, since the Odo shows only the kWh used while driving (it doesn't measure the drain while you're parked...but your rated range will go down). That said, the numbers are pretty hard to rationalize. Even at 92% charging efficiency, the vampire drain would make it nearly impossible to get to 90%. For example, since even if you drive quite a lot, the vampire eats about 15% of the amount of energy you use driving. When I plug 92% charge efficiency in and even cut the vampire to 150 watts (all the measurements I've made and seen show it is higher than that), I still can't get above 83% end-to-end. So, I guess either I have a calculation error someplace or maybe the measurements aren't exactly what they seem to be.

Here is a thread with more drivers' estimates of charge efficiency: http://www.teslamotors.com/forum/forums/charging-efficiency-0 - most of the drivers who have a meter on their charger are seeing 70-80% overall with vampire loads, etc.

Tommy · Apr 19, 2013

You are are correct, the March numbers are reversed, otherwise we would be talking about the perpetual energy aspects of the car instead of vampire loses.:wink:

I take the readings at the close of my electric billing cycle each month. The numbers are vary accurate; I have compared the household use only number to last year's energy use. Very small variance in these numbers. My efficiency numbers are correct.

Remember, my January 90% efficiency was with sleep mode enabled, there would be very little vampire loses in this mode.

Tesla hasn't made it clear where the "up to 92%" efficiency claim is being measured at. Is it the charger itself or at the wall? With sleep mode enabled or disabled? Based on my empirical data, it appears the measurement is from the wall and with sleep mode enabled. That would be logical in that the EPA also measures at the wall to get their ratings and it would be bad PR if Tesla was not able to get close to EPA's published numbers.

bellwilliam · Apr 19, 2013

great job !!
thanks.

this is pretty depressing......
I used S350 Blutec as a reference ICE...and my savings are dismal....
I also use ~390 wh/mile.....

qwk · Apr 19, 2013

Unless you have a dedicated meter to measure wall to wheel efficiency, and take measurements at close to the same ambient and battery temps., the numbers can be all over the place.

With temps in the high 30's to mid 40's F, charging at 239V and 39/40 amps gives me about 29-30 rated miles in one hour, and takes almost exactly 10kwh from the wall. Charging at 118-119V and 12A, takes almost 11 hours and 14.5 kwh to get the same 29-30 rated miles. The sad thing with my 4.2 firmware, the cost is close to the same because the vampire steals the efficiency of the full 240V 40A charging when the car sits not charging. With the 119V 12A charging, it seems like the car is always charging, therefore the vampire load is not as noticeable. If it wasn't for the vampire load, this car would get close to the same wall to wheel numbers as the leaf if driven conservatively.

Cliff Hannel · Apr 19, 2013

I updated the chart to incorporate some recommended tweaks. You can download the Excel sheet from http://EVTripPlanner.com/TeslaOperations.xlsx and plug in whatever numbers make sense for your situation.

Tommy · Apr 19, 2013

Good points @qwk. 4 factors that support my efficiency numbers, and which might partially explain why others have poorer numbers.

I use a dedicated meter; no guess work as to the kW used.

My readings are done on a monthly basis; this averages the "good" and "bad" charging days. The "good" days are the days the temperature, charging rate, time to charge are all ideal. I don't know what that exactly entails, just know that taking a monthly reading vs a daily reading that the true wall to wheel efficiency will be better represented.

I drive a lot of miles: 12k in 4 months. The above average miles driven minimizes the effect of the vampire losses on a percentage basis.

I live in Calif. Cold weather is not a factor in energy being used to heat the battery.

Cliff Hannel · Apr 19, 2013

at 3000 miles/month and 87.5% charging efficiency with 375 Wh/mi displayed, overall efficiency is up to 80% with my model - our numbers do start to converge. At 92% charging efficiency, it hits 85% overall.

shokunin · Apr 24, 2013

Switch your Socal Edison electrical rate plan from domestic to the new TOU-D-TEV (home & electric vehicle) and pay $.09 (summer) or $.10 (winter) price per kWh (same price for Tier 1 and Tier 2) during super-off peak from 12am to 6am.

I am surprised the price per kWh was reduced in the new TOU SCE plan. It used to bump up to $.20/kWh when you hit tier 2 (>130% baseline), but now the rates appear to be the same for both tier 1 and tier 2 (according to the SCE website).

user497 · Apr 24, 2013

Hopefully this isn't off topic: often times when there is an article about EVs people in the comments claim that EVs require more energy to create and are less recyclable. I think this is mostly due to the mining of lithium and creation of the batteries. For example see: The Electric Carâ€™s Short Circuit by BjÃ¸rn Lomborg - Project Syndicate

For starters, the manufacturing process that produces electric cars – especially their batteries – requires an enormous amount of energy, most of it generated with fossil fuels. A life-cycle analysis shows that almost half of an electric car’s entire CO2 emissions result from its production, more than double the emissions resulting from the production of a gasoline-powered car.

While people are quick to talk about the cost to manufacture the EVs, I have never seen anyone calculate the electricity required to build oil wells and refineries. Does anyone know of a true apples to apples comparison from the construction of the car to the energy required to run the car (gas or electricity) for 10 years when you factor in all the hidden costs (for the sake of argument not factoring pollution)? It's hard to argue with the trolls without this data.

bellwilliam · Apr 24, 2013

shokunin said:
Switch your Socal Edison electrical rate plan from domestic to the new TOU-D-TEV (home & electric vehicle) and pay $.09 (summer) or $.10 (winter) price per kWh (same price for Tier 1 and Tier 2) during super-off peak from 12am to 6am.

I am surprised the price per kWh was reduced in the new TOU SCE plan. It used to bump up to $.20/kWh when you hit tier 2 (>130% baseline), but now the rates appear to be the same for both tier 1 and tier 2 (according to the SCE website).

Electric Vehicle Rates | Electric Vehicles | Your Home | Home - SCE
with a Tesla S, you are sure to hit tier 2.
in summer, that's 47 cents / kwh for 10am-6pm and 31 cents for the rest (other than 12am-6am)......I don't think this will work for most..

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REAL efficiency and electricity costs

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