what to pay for residential charging from an outlet

[BMW4Me]

So far I've been lucky enough to find free charging around apartment building or work. Now my building is suggesting that they may allow me to install a standard outlet (L1) by my parking spot and pay for the electricity I consume.

So I'm trying to figure out how much this might cost, in electricity, excluding any electrician who needs to run a standard outlet to my parking space. The building is an older building without a lot of excess capacity, so L2 is out of the question. Also, if I top off every day or every few days from L1 this more than satisfies my commuting requirements.

I googled what kWh rates are in my area and found a range from $.09 - $.11 (this may not be totally accurate is it was a very superficial search). The building I'm in may have even better negotiated rates.

Next, I went into my ChargePoint account and looked at my charging history. The most energy I used for any single charge was just shy of 20 kWh when I was close to empty.

So if I multiply $.10 (average) x 20 kWh (maximum energy used) I get $2.00. Does that mean that if I was to pay the building for every charge I would owe them $2.00?

I want to make sure that I'm calculating this correctly, because if I'm forced to move to a metered solution, this will involve additional upfront and on-going costs which in my estimation will never be paid back.

 

[ted99]

Similar situation for me, except I have a Level 2 charger. At the current reduced charging rate, I compute 5 Kw average load and 4 hours for a complete charge. I have the Rex, so I run the car down to when it starts the Rex, so I have a pretty consistent 20 Kw-Hr per charge. I charge an average of 5X per month, totaling 100 Kw-Hr. At $.10/Kw-Hr, that equates to $10/month. When the chargers get fixed and the charging rate goes back up to 7.4 Kw-Hr, the charging time should decrease, giving roughly the same 20 Kw-Hr per charge. This is actually more generous to the Condo because the charge rate is reduced from the 22 amps for the last 20% of the charge.

You can do the same kind of calculation for level 1 using the 110 v. charging current and your time to charge. More difficult for you if the charge is different for each charge.

 

[Tomasz]

So if I multiply $.10 (average) x 20 kWh (maximum energy used) I get $2.00. Does that mean that if I was to pay the building for every charge I would owe them $2.00?

Close. Your i3 has a 19kWh (give or take) battery pack. So in ideal world you would use 19kWh to fully charge it. Since the process has some loses you have to add about 20% on L1 to that. So from empty to full it'll be about 22kWh (less if you weren't completely empty). National average is $0.12 per kWh so your $2 per full charge is pretty close.

Suggestion - go to a hardware store and buy yourself one of those plug in meters - http://www.amazon.com/P3-P4400-Electricity-Usage-Monitor/dp/B00009MDBU/ref=sr_1_1?ie=UTF8&qid=1418247902&sr=8-1&keywords=power+meter and plug it in when you charge, you'll get very accurate readings how much you actually draw from the grid.

 

[jadnashuanh]

If you'd like to know, verses guess, pick up a Kilowat meter and actually measure it. Most of them will work at up to the 12A the i3 uses.

Also, keep in mind that if you want to buy an EVSE, they do make smaller ones than the 32A the i3 needs to charge at its maximum rate. You could buy a 16A one at 240vac and have almost 3x the charging rate AND 240vac is more efficient (IOW, you'll use less from the wall to charge the same battery in the process). Essentially the same size wiring (well, it would need to be 12g for 20A, and only 14g for 15A, but still only 12-2 - no neutral needed or desired). Depending on the length of the run, you might need to go bigger gauge wires. And, if you wanted a 20A EVSE, you'd need to run bigger wire than 12g, which starts to get expensive partly because of the wire cost, and because it is not as easy to run.