How many solar panels does an electric car need?
An EV driven 12,000 miles a year uses about 3,600 kWh. Here is how many extra panels that takes in 19 American cities. In a typical city that is about 7 extra panels (2.7 kW), or $6,900–$10k added to the system price.
| City | Extra kWh a year | Extra kW | Extra panels | Added cost |
|---|---|---|---|---|
| Seattle, WA | 3,600 | 3.2 | 8 | $9,600 |
| Portland, OR | 3,600 | 3.1 | 8 | $9,200 |
| San Francisco, CA | 3,600 | 2.4 | 6 | $7,100 |
| Los Angeles, CA | 3,600 | 2.1 | 6 | $6,300 |
| Phoenix, AZ | 3,600 | 2.0 | 5 | $6,100 |
| Las Vegas, NV | 3,600 | 2.0 | 5 | $6,000 |
| Denver, CO | 3,600 | 2.2 | 6 | $6,700 |
| Salt Lake City, UT | 3,600 | 2.3 | 6 | $6,900 |
| Dallas, TX | 3,600 | 2.5 | 6 | $7,400 |
| Houston, TX | 3,600 | 2.6 | 7 | $7,700 |
| Minneapolis, MN | 3,600 | 2.7 | 7 | $8,200 |
| Chicago, IL | 3,600 | 2.9 | 7 | $8,600 |
| Detroit, MI | 3,600 | 2.9 | 7 | $8,700 |
| Atlanta, GA | 3,600 | 2.6 | 7 | $7,900 |
| Miami, FL | 3,600 | 2.4 | 6 | $7,200 |
| Charlotte, NC | 3,600 | 2.6 | 7 | $7,700 |
| Washington, DC | 3,600 | 2.7 | 7 | $8,200 |
| New York, NY | 3,600 | 2.8 | 7 | $8,300 |
| Boston, MA | 3,600 | 2.8 | 7 | $8,500 |
Assumes 12,000 miles a year at 0.30 kWh per mile. South-facing roof, $3.00/W. Rough planning figures.
What the table doesn't show
When you charge matters. Panels produce at midday; most people plug in at night. With full net metering the timing doesn't matter. Under net billing, charging at midday (weekends, working from home) is worth more.
A car battery is not a home battery: most EVs cannot power your house in a blackout unless both car and charger support bidirectional charging.
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