The short answer
If you charge your EV with solar, winter is the hardest time of year. Your car needs more energy just when your panels make the least. In a place like Columbus, Ohio, covering a daily commute with solar alone can take almost three times as many panels in January as in July.
The good news is that you don't need to cover your roof in extra panels. Most people get through winter in other, cheaper ways. First, here's what's going on.
Hit #1: your car needs more energy
A gas car turns most of its fuel into waste heat, so in winter it just sends some of that heat into the cabin. An EV is so efficient that it makes very little waste heat. To keep you warm, it has to run a heater from its battery, and it also has to keep the battery itself warm.
That adds up. Recurrent studied more than 10,000 EVs and found the average one lost about 30% of its range at freezing (32°F / 0°C), compared with its best range in mild weather. The Tesla Model Y did a bit better, losing about 24%.
Hit #2: your panels make less
In winter the sun sits lower in the sky, days are shorter, skies are often cloudy, and snow can cover your panels. Using PVWatts data for Columbus, Ohio, one 400-watt panel makes about 1.87 kWh a day in July, but only about 0.84 kWh a day in January. That's less than half.
What that means for one Ohio driver
Let's put both hits together. Picture a driver in Columbus with a 2024 Tesla Model Y Long Range, driving 40 miles a day to work and back.
July: the Model Y uses about 29 kWh per 100 miles (EPA), so 40 miles takes about 11.6 kWh.
January: losing 24% of its range means the car needs about a third more energy per mile (29 ÷ 0.76 ≈ 38 kWh per 100 miles). Now 40 miles takes about 15.3 kWh.
Here's how many panels it takes to cover that drive with solar alone, made on the same day. Panel output is from PVWatts data for Columbus, as published by The Green Watt. These figures allow for a bit more loss than our calculator's 18% default, so treat the panel counts as a cautious estimate. Winter energy use is a rough estimate based on Recurrent's range-loss figure.
| Month | Car's energy use | Energy for 40 miles | One panel makes (per day) | 400 W panels needed |
|---|---|---|---|---|
| July | 29 kWh/100 mi | 11.6 kWh | about 1.87 kWh | 7 |
| January | about 38 kWh/100 mi | 15.3 kWh | about 0.84 kWh | 19 |
What the numbers mean
Seven panels in summer, nineteen in winter. A system sized perfectly for July leaves you buying a lot of grid power by December.
You don't need 19 panels: 1. Let summer pay for winter (if your utility allows it)
Over a full year, the same driver needs about 13.4 kWh a day on average, and one panel makes about 1.36 kWh a day. So about 10 panels cover the whole year's driving, not 19.
This works if your utility offers 1:1 net metering with credits that roll over from month to month. In summer, your panels make more than the car needs, and you bank the extra as credits. In winter, you spend those credits on grid power. If your utility pays less for exported power than it charges you, the plan only partly works. Check your utility's solar rules, or look them up on DSIRE (dsireusa.org), before you size your system this way.
2. Warm the car while it's still plugged in
Most EVs let you preheat the cabin from an app or set a departure time. If you do this while the car is still plugged in, the heat comes from your home's power instead of the car's battery. You leave with a warm car and a full battery, and you lose less range on the way.
3. Keep your panels clear of snow, safely
Cold itself isn't the problem. Solar panels actually work a little more efficiently in cold weather, so a cold, sunny day can be a good one. The problem is snow. A thick layer can stop production almost completely. Snow usually slides off tilted panels within a few days. If you want it gone sooner, use a soft solar-panel rake from the ground, and check with your installer first. Never climb onto a snowy roof, and don't scrape the glass.
An example: Greg in Ann Arbor, Michigan
Greg lives in Ann Arbor, where DTE Energy supplies his power. He drives a 2024 Ford Mustang Mach-E AWD Extended Range (34 kWh per 100 miles, EPA) about 40 miles a day. In summer, that takes about 13.6 kWh.
His installer added 12 panels for the car and told him they'd cover his driving all year. In July, they did easily, making around 22 kWh on a typical day.
Then winter came. Recurrent found the Mach-E loses about 36% of its EPA range in freezing weather, so Greg's car now needed about 21 kWh a day for the same drive. At the same time, his 12 panels were making only about 10 kWh on a typical January day. He was buying around 11 kWh a day from the grid.
Over a full year, his panels make almost as much as his car uses, so with 1:1 net metering his summer extra would have covered most of his winter shortfall. But DTE replaced net metering for new solar customers in 2019. Under its newer "inflow/outflow" billing, the credit for exported solar dropped by about 45% compared with the old rules. So Greg's summer credits covered only part of his winter charging.
The installer's promise wasn't crazy. It just assumed full net metering. Before you size a solar system for your EV, find out exactly how your utility credits the power you export.
Greg is an example, not a real customer. Michigan winters are often cloudier than Ohio's, so his real output could be even lower.