Electric Vehicles, Solar Energy and Net Metering

It’s an interesting combination in more ways than one. As there are no production or transportation costs for solar, beyond initial installation, home solar/ EV driving makes for one of the most efficient way to drive electric. Further, costs of owning an EV as well as home solar is more affordable than ever.  In fact, roughly 1 in 3 EV drivers have a home solar.  As Elon Musk said at a recent press conference, “We have this handy fusion reactor in the sky called the Sun. You don’t have to do anything, it just works. It shows up every day and produces ridiculous amounts of power.”

Driving our i3 BEV for almost a year put us on a crash course of learning how electricity is quantified, produced, transported, and consumed. First to understand how electricity measured you need to know what a kWh is, think ten 100 watt light bulbs burning for an hour and that’s a kiloWatt hour.

The sun’s energy can be harnessed several ways but the most cost efficient for individuals and homes are solar panels. Solar energy systems produce direct current (DC), however households use AC. So, our solar system has two Sunny Boy 5000TL US-22 inverters which convert the solar energy captured by our 48 Canadian Solar panels from DC to AC which is then put into the breaker panel. Outside of some switching noises in the morning when the inverters turn on, they don’t hum or make noise. These inverters have continuous output display panels on them and are connect to the internet to allow us to track the production anywhere.

Next, figuring out how far the i3 could go on a single charge was a little more difficult because of varying driving conditions that effect efficiency. The i3 has a 22 kWh (kiloWatt hour) battery pack but its use able capacity is 18.8 kWh. Most months we are able to go about 5 miles per kWh which falls right in line with the as advertised 80-100 mile range on a single charge. However, we have found this to be rather variable depending on weather and how it’s driven.

Interestingly, the i3 is more efficient in the city stop and go traffic of less than 50 mph, than it is at 75 mph on an interstate, whereas “ICE” internal combustion engine autos are more efficient on the interstate. We experienced no difficulty getting around in the snow with our i3 while driving shod with snow tires, though the bitter cold, arctic winter can dramatically shorten the range of of the i3 and all electric vehicles. See here for winter driving review.

A little over a year ago, we had a 12 kW Solar system installed on our home. In 14 months, it has produced 17.58 MWh (megawatt hours) which has been more than we have consumed over the same period even factoring charging of our i3 BEV doing 1000 miles a month. Obviously we consume electricity when are not producing, namely at night, during storms or when covered in snow. So we still have a monthly bill to pay, but it’s not much. The amount of electricity in kWh we produce in excess of production is credited each month and then subtracted from our usage in kWh from the grid. This is called Net Metering and many utilities have it. They do not credit us 1:1 for each kWh we kick into the grid because of the costs of maintaining the grid, power lines etc. In the last 4 months, our electric bill has been $74 – $44 of which is a “customer charge” for being hooked up the the grid.

*Editor's Note: The remainder of this post by Chuck Vossler appears on BMWBLOG. Check it out here.