Two Months Driving on Zero
in my Nissan Leaf

May 23, 2012

Mark D Larsen

2012 kWh Distribution To Date

I received my monthly bill from Rocky Mountain Power today, and was amazed to see that my solar array still produced far more electricity than I needed, despite the fact that I am now using several kWh per day to charge an electric vehicle. The following graph plots how many kWh I have pulled from the grid at night (grey), how many extra kWh my solar array puts into the grid in the day (light blue), and the line (blue) traces the difference between the two sources from month to month since the beginning of the year. For example, according to today’s bill, during the last 31 days I pulled 592 kWhs from the grid at night, put 1,319 extra kWhs into the grid by day, and thus “deposited” an additional 727 kWhs into my “savings account” with Rocky Mountain Power.

Coincidentally, it has been nearly two months since I took delivery of my Nissan Leaf, so I was curious to see how charging it has affected my solar production. Sure enough, as the above graph shows, the utility kWhs rose during April and May, since I almost always charge at night when demand is at its lowest. Nonetheless, the amount of excess electricity I put into the grid by day for the last two months still more than compensated for that extra load.

You can see the overall results to date in the pie chart at the top of the page. Obviously, charging the Leaf has a long way to go before the sum of those kWh plus the other utility kWhs at night would equal all the excess kWhs I am generating in the day. I will be very curious to see how the slices of the pie change shape next fall and winter, when the days grow shorter and the angle of the sun lower in the sky. My hope is that my “savings account” will have accrued sufficient kWhs to cover all our needs in both the home and the car for the entire year, regardless.

It is also worth noting that I have driven my Leaf a total of 1,761 miles on the 345 kWh used for charging in the pie chart. That works out to an average of 5.1 miles-per-kWh —much higher than the EPA’s official estimate. Of course, I typically drive in ECO mode, unless I need to merge onto a freeway, pass a vehicle as quickly as possible, or humble a naysayer at a stoplight who dares to call it a “golf cart.” Still, with 21 kWh useable in the Leaf”s 24 kWh battery pack (3 kWhs are always held in “reserve”), that really does amount to a range of 100 miles per full charge.

What is most impressive of all? That so far I really am driving for free, and producing zero greenhouse gases, thanks to my solar array. So much for the “long tailpipe” accusations of petrolpuppets!

COMPARISON Fuel Costs GHG Produced
Actual Results with my Solar Array $0.00 0 lbs.
IF I had charged from the grid instead $29.99 582 lbs.
IF I had driven our Subaru instead $366.16 2,157 lbs.