Electric Cars, Solar Panels and Your Power Bill
As more and more people add electric cars, it comes as a shock for some to see how much their power usage goes up! Obviously they’re just shifting a part of their transportation budget to their utility bucket, but it can look shocking, and it brings up a few questions. One is: how many solar panels do I need to add to offset an electric vehicle? Another is: is it worth it to go electric? Am I actually saving money? Another one might be: if I charge off the grid, isn’t that just as bad as driving a fossil-fueled vehicle?
I want to help you answer each of those questions. I built a tool that lets you select your vehicle’s MPGe and a few other factors the main calculator uses, and it addresses each of those questions. It lets you toggle, turn and manipulate the various factors and see how it would work in real life. It even lets you see how much carbon is emitted with different choices, equated to trees, because that makes it simple to see. You’ll see it is possible to offset your driving with solar, but it isn’t always easy. On most grids, it is still a very good choice to switch to an EV, from both a financial and an environmental standpoint.
How many panels?
A typical electric car gets about 112 MPGe. Driven 12,000 miles a year, it uses about 3,600 kWh. Covering that takes five to eight panels facing south, depending on where you live: five in sunny places like Phoenix or the Bay Area, eight in Seattle or Portland. That’s 110 to 175 square feet of roof. An SUV or pickup can need ten or more.
The catch is that making a year’s worth of power isn’t the same as charging from the sun. Winter falls short, and the car is often plugged in at night. On net metering that doesn’t matter much, because summer’s extra is banked for winter. On net billing, like California’s, it matters a lot. That’s where it stops being easy.
Am I actually saving money?
Usually, yes, even before solar. Your power bill goes up, but your gas bill goes away. In the Bay Area, with electricity at $0.41 a kWh and gas near $5.86, the same 12,000 miles cost about $1,480 to charge against $2,510 of gas: about $1,030 a year saved. Where power is cheap, the gap is bigger: about $1,500 a year in Chicago and $1,750 in Seattle.
Panels then save you the charging bill too, but that’s solar’s saving, not the car’s, and panels cost money. The rooftop calculator works out whether they pay for themselves.
Isn’t grid charging just as bad as gas?
No. A 28-MPG gas car driven 12,000 miles burns about 430 gallons and puts out about 3,800 kg of CO₂ a year. It would take about 63 trees to soak that up. The same miles in an electric car, charged from the grid, put out 55% to 82% less, depending on how your grid makes its power. The cleanest grid in the tool is California’s, at about 700 kg a year (12 trees); the dirtiest is Colorado’s, at about 1,700 kg (28 trees). Every grid I have numbers for comes out well ahead of gas, and grids are getting cleaner every year.
Add enough panels to cover the car’s year and its share of the grid’s carbon drops toward zero.
Try yours
Put in your car’s MPGe, your miles and where you live in the electric car calculator. The prices and the grid’s carbon fill in for your area, with where each number came from, and you can change any of them. Try fewer panels, a less efficient car or a dirtier grid, and watch what moves.
The tool counts what comes out of the tailpipe and the power plant. It doesn’t count building the car, the battery or the panels. The tree figure is the EPA’s: one city tree in its first ten years takes up about 0.060 metric tons of CO₂ a year.