# Foren

ZUR TESLA-COMMUNITY

Cost of an overnight charge?

Idaho Power charges \$.0899 per kwh. How do I calculate what the cost is for a full charge overnight (assuming I needed to charge for 300 miles)? I would love the answer to be 9 or 10 hours x \$. 0899 but think that is wishful thinking (and bad math).

Vielen Dank!

There usually are transmission charges as well.

Volts times Amps = Watts; Watts divided by 1000 = Kilowatts

When you plug in you will see the charging rate (volts and amps) on the dashboard. You will also see the estimated time to charge.

Multiply Kilowatts times time to get Kilowatt-hours.
Multiply this time \$0.0899 to get an approximate cost. Since there are losses in the system this number should be increased by 10-25%. Maybe someone else has a better understanding of the losses.

Cerjor- thank you!

You're going to fill up for 10 bucks and get change back.

The think that you forgot is to multiply by the kwh you draw. A 40 amp circuit at 240 volts is 9600 watts, or 9.6 kw. Run for an hour, it's 9.6 kwh. So if you take your math above and multiply it by 9.6, you'll be closer. You could also work it out based on your battery pack. Remember, your pack will never be completely empty or full, and you have some charging losses.

grab my spreadsheet at http://EVTripPlanner.com/calcs.php - it has true electricity costs accounting for efficiency, vampire losses and electricity rates you enter.

Around \$2 ??

jbunn....thank you for confirmation. That is how I did the calculation after cerjor gave us the math. So, 9.6 x \$.0899 x 9 hours = \$7.77. so, rounding and "losses" probably means about \$8.00 to go 270-300 miles. Less than \$2.00 per night on my normal driving commute each day!

I love this and can't wait until June 10!!

Here in Seattle City Light territory, a kwh costs 5 cents for business accounts, so \$4.30 for a 300 mile fill compared to \$75 at the gas pump.

It is also sourced 98% from hydro, wind, and solar. The 2% fossil fuel component is likely coming from natural gas during peak demand hours, not nighttime charging hours, so it's as close as you are likely to get to avoiding fossil fuels for filling up.

Of course, you will need to move to Seattle or Switzerland (the other 98% place).

My measurements shows about 86% of the electricity that passes through the breaker box ends up in the battery (YMMV, and it does vary a bit depending on the charge level and charging speed), so a 0-100% charge would be 85kWh / .86 = 98.8kWh * \$.0899/kWh = \$8.89.

In addition, there will be some losses from running the computers in the car, which are about 150W, or about 3.6kWh/day costing you another \$.32.

Check to see if you can get hourly billing if the electric company offers a smart meter. In chicago, standard rate is 7.2 cents but with hourly billing is varies as high as 14-20 cents during peak and as low as 1-2 cents at 2am. I charge at 230 am every night and put a dedicated meter on the line feeding the hpwc ... my average cost per mile all in based on electricity flowing across the wire is 1.5 cents. It sounds ridiculous and too good to be true but i have the electric company bill that tells me I've saved over 50 percent (\$1000) since moving to hourly billing. I had the smart meter installed before taking delivery and started saving \$50 a month immediately. Basically, I never would have thought about a smart meter before the car so my optimistic view is that the car covers its own fuel cost. We use more electricity overnight comparatively to neighbors due to some heated floors.