7 Months of Mostly Free EV Charging

It has been 7 months already and we've put over 5,850 miles on our electric car. During that time we've charged 196 times at 11 different charging stations, and never once paid for gas or waited for the tank to fill. One of the great things about electric vehicle charging stations, particularly those from ChargePoint is how they are networked and provide an online dashboard where you can view personal charging history and energy consumption. Our home charging station has a built in cellular uplink and is connected to an online account so all charges from home are automatically visible on the website. At public charging stations I scan an RFID card on my keyring to associate the charge with my account.

Using this website, I see that of those 5,850 miles, I used over 2,114 kWh of electricity. 27% of that electricity was consumed overnight by our home charging station in our garage, and the other 73% was provided free by the charging stations at my employer or the free charging stations at San Francisco city parking garages.

In our first month of owning the car, we didn't even have a home charger, and so we were charging exclusively for free, but not really putting that many miles on the car each day. Now that my wife is commuting further to work each day, we put over 50 miles a day and charge it up at home each night and at a parking garage in San Francisco each day while she is at work.

If we assume an electricity price of $0.12 per kWh, then it cost 2,114 * 27% * $0.12 = $68.49 in electricity to drive those 5,850 miles. Gas is approximately $5/gallon in Silicon Valley right now, so $68.49 would buy less than 14 gallons of gas (1 tank!). I'd have to get 418 miles per gallon to come out ahead with a gas car given how much of my driving is subsidized by free electric vehicle charging stations.

First Month of Experience with ChargePoint

Update 4/6/2012: Thanks to a former colleague who now works at CoulombTech for pointing out a minor error in this post.  The Charge Point cards use RFID rather than barcodes.


We've had our ActiveE for over a month, but still don't have a home charger.  Over the past month we've put over 1300 miles on the car, and have charged exclusively at ChargePoint units at my office and at public charging stations.  To use a ChargePoint charger you first scan a barcode an RFID card to authenticate and then just plug in the standard J1772 connector to the car.  The fact that you scan in each time means that you can track your charging status and history precisely on the ChargePoint website or mobile application.


Some of the older ChargePoint chargers will cause a GFCI hard fault when you first start to charge with an ActiveE.  This is an issue that has been addressed in newer ChargePoint chargers and you can just retry if you ever experience this.  It was disconcerting to see this error on my first attempt to charge the car last month, but every ChargePoint charger includes an 800 number and the technician on the phone was able to monitor the station in real time and advised me to try again until we got it working.
I now find that this GFCI fault occurs in about one attempt out of three or four with an older ChargePoint unit, but it always succeeds on a second try.


Over the last month we've visited 6 different charging stations and consumed 447 kWh with the car.  ChargePoint claims that this is the equivalent of 635 kg of greenhouse gases saved, but that seems way too high so they must be comparing against a very inefficient internal combustion engine car to reach that figure.  This is presumably calculated using the emissions of an average gasoline-powered car and subtracting the emissions generated for the electricity to charge this electric car.

Using the EPA Clean Energy Greenhouse Gas Equivalencies Calculator I get a value of 308 kg of CO2 generated for the creation of the 447 kWh of electricity we used.  In my case this is a large overestimate because almost all of our charges have been from Solar powered electricity.  Our primary chargers at work are solar powered, as are the chargers at the Portola Valley Town Center.  The videos below show a bit of the charging infrastructure we've been fortunate enough to use.