Roadster winter efficiency

The Roadster shows on its display the amount of energy used to charge it, and the cost, if you have entered your cost per kWh. But unless there's something I have not found, it shows it for only a moment when the car is turned on. So this morning I made a note of energy and cost, as well as yesterday's miles.

It's been cold (for Spokane) here lately. Yesterday I drove downtown, 31.7 miles total. I drove there on the surface roads, with lots of jackrabbit starts. Any time I was first at the light I floored it from zero up to the 35 mph speed limit. The car has very agressive regen so I don't need to use the brakes a lot. I had the heat cranked up to keep the cabin toasty warm. On the way back I took the freeway, driving 65 to 70 mph, but more 65 than 70. Again, hard acceleration to pass. This car was made to be driven hard. And again, lots of heat.

Charging took 71 cents worth of electricity (I pay 6 cents per kWh). And as I said, I drove 31.7 miles.

That means it cost me 2 1/4 cents per mile for the electricity. This is the cost to recharge the battery, so it's measured from the wall and includes all the electricity used to heat the cabin and to cool the battery during and after driving and while charging. That works out to 2.68 miles per kWh with cabin heat and battery cooling.

I'd say that's not too bad for hard driving in Spokane-cold weather, which, admittedly, is a far cry from North Dakota cold, but is colder than Seattle. It's also in line with the 3 miles per kWh that I guesstimate for summer driving. (I've never used the A/C. In warm weather I take the top off, and in very hot weather I put on the mesh top, which gives partial shade while allowing lots of air flow. The mesh top is an aftermarket item made and sold originally for the Lotus Elise, with which the Tesla shares a frame and body.)

 

Same test. Different day, similar drive. 368 Wh/mile, 2.21 cents per mile. And I finally found the menu item to see my charging history so I don't have to look and remember when it flashes briefly on start-up. Again, this is driving hard and running the heater for a toasty-warm cabin.

I'll do it for a long drive without heater once spring comes and we get some warm weather.

 

Presumably it has a power meter analogous to a Kill-a-Watt meter, and if there are losses in the UMC (effectively an EVSE) it knows how much those are.

The reading appears at the end of the charging period, showing time taken, kWh used, and the cost of the electricity (if you've entered your electric rate). Thus, I can find out the next day how much electricity I used. The trip odometer tells me how far I drove, assuming I remembered to reset it, which sometimes I do.

 

P.S. For all I know, the meter could be in the UMC, and the data transmitted to the car.

 

Not sure. I don't know if the history goes all the way back, or if it scrolls off the screen and disappears. I'll check. The accuracy would be only moderate, however, since it's given in whole kWh for each charge, and I have a lot of small charges as I often drive 3 miles to the store and back and then plug in. I'm also not sure I'd want to bother adding up six months of almost-daily charges.

I'm not as anal as some about tracking lifetime energy usage. When I tried to track my Prius gas usage I kept forgetting to write down the figures. I'm satisfied just knowing that in summer I generally get about X and in winter about Y.