In February, my PV system produced 331 kWh that I would have otherwise had to purchase from PG&E. That represents about 85% of my EV charging for the month, which at my average per-kWh price for charging ($0.1547) would have meant another $50 of electricity. Without the PV-generated electricity, the charging cost would have been higher, since our overall electricity usage would have climbed into higher (and more expensive) tiers. In fact, the incremental cost of charging the EV would have made all of my electricity more expensive, but my PV system essentially erases that penalty.
There are so many numbers and extenuating factors and circumstances, but for the sake of argument, nearly all of my EV’s fuel costs could be considered offset by PV-generated electricity. This decreases the payback period on my PV system—just as the cheaper electricity decreases the payback period of purchasing an electric car.
The savings are greater during May’s sunny days—that’s when my PV system’s output jumped to 603 kWh (nearly double February’s production). I also stopped running my heating system, which uses a lot of electricity to power its fan. Most of May’s EV charging was during off-peak hours, which range in price from $0.03 to $0.198 per kWh. Only about 15% of the time did I succumb to charging during the peak times of 2 to 9 p.m. By the end of the month, these prices had shot up to more than $0.50 per kWh.
In May, with greater PV production, our adjusted electricity use, which factors in PV production and utility consumption, was 461 kWh. My driving in May also eased off to 341.76 kWh, down from 385.12 kWh in February. In May, the total cost for the 1,128 miles of EV driving was $47.40—an average of $0.139 per kWh.
In May, if I had exclusively charged the EV between midnight and 7 a.m., I could have reduced costs from $47.40 to $30.64. Still, the $47.40 is nearly one-third of the $113 gasoline bill I would have had fueling a 40 mpg gas car at $4 a gallon.
The PV system generated 603 kWh in May, helping charge my Leaf (which used 341.76 kWh) and offset at least one-third of my home’s electricity use during that month. Without the PV system’s contributions, the portion of my electricity usage in the higher tier would have been greater, driving up the overall cost of recharging the Leaf.
How does all this stack up to the $0.02-per-mile value that gets tossed around? In February, my EV fuel costs were $0.047 per mile. In May, they were $0.042 per mile. That compares to about $0.10 per mile for a 40 mpg gasoline-engine car in those months.
While my cost was a little more than double the common EV claim—which says EVs cost one-sixth as much to fuel as gas-powered cars—I probably could have gotten quite close to the promise of big EV cost savings if I had charged the Leaf only in the middle of the night; driven it more efficiently; and compared it to a 30 mpg gas-powered car instead a 40 mpg one (the national average for a new passenger car is currently about 23 mpg).
But thanks to solar and electric-drive technology, even with my lead foot and a charge-when-I-want-to attitude, I’m able to cut the cost of vehicle fuel by more than half. And to me, the reduction of carbon in the environment and the displacement of oil use—from a supply chain fraught with economic and political dangers—are absolutely priceless.
Bradley Berman writes about green transportation, contributing to The New York Times, KQED Public Media, PluginCars.com, and other publications. He is a research analyst for Pike Research—a clean technology market research firm—and serves as a consultant to eBay’s Green Driving Center.