How Many Solar Panels Do You Need to Charge an EV?
Adding an EV to a solar home is one of the most common reasons systems get bigger. Here's how to work out what your car actually needs, and when those extra panels pay off.
A typical EV driven 12,000 miles a year uses about 3,000 to 5,500 kWh of electricity, depending on the vehicle. Covering that takes roughly 6 to 10 extra 400 W panels in a sunny state, and more where there's less sun. Whether adding them pays off depends on when you charge and how your utility credits solar.
How to calculate it
Three numbers do the work: how far you drive, how efficient the car is, and how much sun your roof gets.
- Energy the car needs: miles per year ÷ miles per kWh.
- Output of 1 kW of solar: peak sun hours × 365 × 0.8 (the 0.8 covers inverter, wiring and heat losses).
- Extra system size: step 1 ÷ step 2. Divide by 0.4 kW to get the number of 400 W panels.
A crossover EV (about 3.4 miles per kWh) driven 12,000 miles a year needs about 3,500 kWh a year, or roughly 290 kWh a month.
- In California (about 5.5 sun hours a day), 1 kW of solar makes about 1,600 kWh a year. That's 6 extra panels (2.4 kW).
- In Illinois (about 4.0 sun hours), the same car needs 8 extra panels (3.2 kW).
At a typical $2.50 to $3.50 per watt, 2.4 kW of extra solar costs roughly $6,000 to $8,400 before any incentives.
Panels for your EV
Enter your driving and your state's sun hours. Your car's EPA rating gives the miles per kWh.
It depends a lot on the vehicle
Here's 12,000 miles a year in a state with 5 sun hours a day:
| Vehicle type | Miles per kWh | kWh per year | Extra panels |
|---|---|---|---|
| Efficient sedan | 4.0 | 3,000 | 6 (2.4 kW) |
| Crossover or small SUV | 3.4 | 3,500 | 7 (2.8 kW) |
| Large SUV | 2.7 | 4,400 | 8 (3.2 kW) |
| Pickup truck | 2.2 | 5,500 | 10 (4.0 kW) |
A second EV in the household roughly doubles the number. If one is likely in the next few years, it's worth sizing for it now, but only if the timing math below works for you.
When you charge matters more than how many panels
Solar makes power in the middle of the day. Most people charge their EV overnight. So unless you charge while the sun is up, the “EV panels” mostly send power to the grid during the day, and the car charges from the grid at night.
- With full net metering (one-for-one credits), that's fine: daytime exports pay for nighttime charging.
- Under net billing, such as California's NEM 3.0, exports earn only a few cents per kWh, while you pay much more for power at night. Extra panels for an overnight-charged EV pay off far less.
Under net billing, the extra panels make the most sense if you can charge during the day (working from home, weekend charging, a car that sits at home) or add a battery. Otherwise, compare against your utility's EV time-of-use rate, which can make overnight charging cheap without any extra panels.
Before you sign: EV checklist
- Main electrical panel: a Level 2 charger usually needs a 40 to 50 amp circuit. Older panels may need an upgrade, which should be its own line item.
- Charger: is a Level 2 charger and its installation included, or separate?
- Rate plan: check your utility's EV or time-of-use rates before deciding how much extra solar to add.
- Room to grow: if a second EV is likely, ask whether the inverter and roof layout can take more panels later.
- Show the EV math: ask the installer to show how many kWh they assumed for the car, and check it against your own numbers.
Red flags
- A system sized for an EV you don't have yet, with no discussion of when you'd buy it.
- EV savings that assume one-for-one net metering under net billing rules like NEM 3.0.
- No question about when you charge, or what rate plan you're on.
- An electrical panel upgrade that appears only after you've signed.
Want the full picture?
The free EV + Solar tool runs this math for any state. For a model-by-model version (23 EVs with EPA efficiency), the home-vs-car panel split and fuel savings against gas, the EV + Solar Sizing Kit is on Etsy ($24).