How do I calculate what it costs to charge my i3?

[RobJones]

I've had my i3 for about a week and am loving it. We named it "Watney" after Matt Damon's character in The Martian because BMW really scienced the **** out of this car!

I've been trying to figure out how much it costs me to charge the car, assuming a fully depleted battery. But I'm not an electrical engineer and have been struggling with the math. Here are the rates from my electric company - Flint Energies (http://www.flintenergies.com):

kWh Charges:

October through May:
All kWh per month: 10.0 Cents per kWh

June through September:
First 4,000 kWh per month: 10.0 Cents per kWh
All kWh over 4,000 kWh per month: 12.0 Cents per kWh
(including Energy Conservation Adder)

*A kilowatt-hour (kWh) is a measurement of electricity. One kWh runs a 100-watt light bulb for 10 hours.

So how can I use this data to figure out what it costs to charge the car's battery?

 

[websterize]

The relative (usable) battery capacity is 19 kW, so about $2 USD per "fill-up."

Watch the neighbors’ eyes widen when you tell them that.

 

[RobJones]

Ah, I see now. Thanks! So, in the worst-case scenario of recharging a completely drained battery every day, it'll cost me roughly $60/month in electricity. Of course, I won't be draining the battery every day so it'll be a lot less than that.

So for roughly the equivalent of filling the tank in my X5 4.6is once, I can "refill" the i3 for a month. Pretty sweet!

 

[jadnashuanh]

Because things aren't 100% efficient, if you needed to fill the batteries with 19Kw, you might need to supply 21Kw or so, give or take a bit. The conversion from acv to dcv is not perfect, and then you may need to run the fan or the cooling circuits during the process. But, as a rough estimate, at $0.10/kw, a couple of dollars is about right. My electrical costs are nearly double that, but it's still a bargain.

 

[Jeffj]

Easy way to estimate is as follows:

Reset your trip computer, drive for a week. See what it says for your "efficiency" - its displayed in mi/kWh. Know that its lower in the winter than the summer, since it takes energy to heat the batteries and car. Depending on where you live, it could be a 30% difference summer to winter.

Estimate your miles/month and divide by the mi/kWh shown. Multiply by 1.25 to account for inefficiencies, pre-conditioning, etc.

So, if you drive for a week and show 3.9 mi/kWh, and you estimate that you drive ~900 miles/month, you'd get
900/3.9 = ~230 kWh * 1.25 = ~288 kWh. @ $0.10/kWh, that's just under $30.