Electric car calculator: panels, cost and carbon

How many solar panels would cover your electric car? Does going electric save you money? Is charging from the grid really cleaner than gas? Put in your car and where you live, and change anything. Why I built this.

Where you live

Fills in the prices and the grid’s carbon below. Change any of them.

Miles a year

Not sure? 12,000 is a typical year.

Your electric car’s efficiency

Gas car to compare (MPG)

The car you have, or the gas car you’d buy instead.

Prices and the grid

Electricity ($/kWh)

Gas ($/gallon)

Grid carbon (kg CO₂ per kWh)

Solar panels

Which way the panels face

NESWN

Drag the panels around the house. The dotted lines are the sun’s path at midsummer and midwinter.

Panel size (watts)

460 W is typical today.

Panels you’d add

Leave it blank for enough to cover the car’s year, or try fewer.

How many panels?

–Panels

–System size

–The car’s electricity a year

–Of it the panels cover

What the panels make, kWh a dayWhat the car uses, kWh a day

Covering the dark months

Am I saving money? Is the grid as bad as gas?

How it works

The car’s electricity is miles ÷ MPGe × 33.7 kWh, the energy in a gallon of gasoline. The EPA’s MPGe is measured at the wall, so charging losses are already in it.
The gas car burns miles ÷ MPG gallons, and each gallon releases 8.887 kg of CO₂ (EPA).
Charging from the grid releases what your grid averages per kWh, from the EPA’s eGRID for your region. A cleaner or dirtier plan changes it, so change the number if yours differs.
Trees: one city tree, in its first ten years, takes up about 0.060 metric tons of CO₂ a year (EPA). So 1 ton of CO₂ a year is about 17 trees.
What a panel makes comes from NLR PVWatts v8 for your area, on a 20° roof facing the way you choose (read between eight measured facings), with PVWatts’ standard 14% losses: the same table the rooftop calculator uses. Roof space assumes about 22 square feet a panel.
Prices start at your area’s electricity price and the EIA’s weekly gas price, each with its source and date. Your own bill and pump beat both.
Not counted: building the car, its battery or the panels, maintenance, and what the panels cost. The rooftop calculator prices solar.

Covering the year isn’t the same as charging from the sun

Panels that make as much as the car uses over a year don’t charge it directly unless it’s plugged in while the sun is up. On net metering, summer surplus is banked for winter and night-time charging, so the yearly total is what counts. On net billing, like California’s, power you send out earns far less than power you buy, so it matters when the car charges. And the car isn’t the only thing using that power.

For what solar is worth in dollars with your rates and your home, use the rooftop calculator. Solar + EV explains why a solar-charged mile is worth your electricity rate, not the price of gas.