Photovoltaic solar panel installation on house, Fremont, California [image: Shiva Singh]
Drivers who buy an electric car that plugs into the power grid to recharge the battery often start to consider the source of their energy.
A 2012 analysis from California, in the earliest days of modern electric cars, indicated as many as four in 10 electric-car drivers were already using or considering the addition of home solar panels to generate electricity.
While we've sought out more recent data on the overlap between electric-car drivers and home solar panels, we haven't found any.
California has been at the forefront of emission reduction and renewable energy for decades, of course, so those 2012 results may not reflect the national average.
But we decided to put the question into one of our weekly Twitter polls, to get a better sense of what today's electric-car drivers use to charge their vehicles.
We asked simply what the source of the electricity used to recharge the participant's electric car. (Our apologies to our non-EV-owning Twitter followers; this one's not for you.)
If you own an electric car, what's your at-home charging from?— Green Car Reports (@GreenCarReports) February 26, 2018
We'd suspect most electric-car owners simply plug in to their local utility's electric grid, and leave it at that.
Doing so immediately reduces the carbon emissions per mile associated with driving, except in a small handful of locations and comparisons.
So that's the first of our four options in the poll.
Following that comes plugging into the utility grid, but also paying for a supply of renewably generated electricity from that grid—an option offered in an increasing number of locations, though not all.
Another step toward more renewable transport is to charge your electric car from grid power in a home that has solar panels and so-called reverse metering, or the ability to feed excess renewable energy into the grid, offsetting a portion of the cost of the home's electricity use.
Finally, the ultimate low-carbon energy for charging a plug-in vehicle is to use off-grid solar or wind power exclusively.
Photovoltaic solar power field at Volkswagen plant in Chattanooga, Tennessee
We suspect that last choice is fairly rare at the moment, though it's been suggested for more rural locations—and will likely get more practical as the cost of home energy-storage batteries continues to fall.
Our Twitter polls are quite limited in format, otherwise we would have added a question that would allow us to correlate the different answers with locations, perhaps just "California" versus "elsewhere."
We'll be curious to see what kind of response we get, and if any reader knows of more comprehensive studies on the intersection of plug-in vehicle ownership and use of renewable energy (whether home solar or renewable power delivered via the grid), do let us know.
As always, please note that our Twitter polls are far from scientifically valid, due to small sample size and self-selection by those who choose to participate.