Solar Panels for an Electric Car: How Much Bigger?
Adding an EV means more kWh per year. See how right-sized solar systems and payback change in four example states, with assumptions stated.
Published 4 min readRoofPayback editorialChecked by automated fact and quality checks
Official data: EIA · DOE · IRS · how we check
In this article · 8 sections
Short answer
An electric car adds a new, steady load to your home. In this guide we assume a car adds 3500 kWh per year. That is an assumption, not a measurement. Your real number depends on how far you drive, your car, and how you charge.
A kilowatt-hour (kWh) is the unit your utility bills you for. More kWh means a bigger rooftop system to cover it. In our example homes, a bigger system cost more up front, but the payback time stayed about the same or got slightly shorter. Payback is the number of years of bill savings needed to repay the system cost.
How we model the car
We treat charging as extra annual kWh on top of what the home already uses. That keeps the math simple and easy to check.
The example home uses these assumptions:
- 7 kW system and 10500 kWh per year of use before the car
- 40% of use happens while the sun is up
- Installed cost of $3500 per kW, with no incentives
- $100 per year for maintenance
- Electricity price rising 2.5% per year
- Panel output falling 0.5% per year
- A 25-year horizon
- Export credits capped at a year of grid purchases, with an annual true-up
Production comes from PVWatts v8, a free estimator from the U.S. Department of Energy's National Laboratory of the Rockies (formerly NREL). We used south-facing panels, a 20° pitch and 14% losses, with one reference city per state. Prices are the August 2026 average residential prices from the U.S. Energy Information Administration (EIA).
What changes in the system size
Right-sizing means picking the system whose yearly output roughly matches your yearly use. Add the car's 3500 kWh and the target moves up.
For a home that used 10500 kWh per year, adding the car brings use to 14000 kWh per year. The right-sized system then changes like this:
| State | Without car (10500 kWh/yr) | With car (14000 kWh/yr) |
|---|---|---|
| Texas | 7 kW ($24500) | 10 kW ($35000) |
| California | 6 kW ($21000) | 8 kW ($28000) |
| Florida | 7 kW ($24500) | 9 kW ($31500) |
| Arizona | 6 kW ($21000) | 8 kW ($28000) |
Sunnier places need fewer kW for the same kWh. That is why California and Arizona need smaller systems than Texas here. Our solar panels guide explains the sizing step in more detail.
What changes in payback
Here is the payback for the same homes, with and without the car.
| State | Payback at 10500 kWh/yr | Payback at 14000 kWh/yr | Year-1 savings at 14000 kWh/yr |
|---|---|---|---|
| Texas | 14.3 years | 14.1 years | $2227 |
| California | 6.8 years | 6.8 years | $3991 |
| Florida | 14.1 years | 13.9 years | $2084 |
| Arizona | 12.5 years | 12.3 years | $2107 |
Payback barely moves. The reason is that the cost per kW stays the same in this model. More use also means each added kWh of solar replaces a kWh you would have bought from the grid. The car does not make solar cheaper. It makes the system bigger, and the savings grow in step.
Year-1 savings are larger with a car because you avoid buying more grid electricity. These are modeled results, not quotes or guarantees.
The daytime-use catch
Many cars charge at night. Solar panels only make power while the sun is up. In our model, 40% of home use happens during the day. If the car charges overnight, you may export solar power by day and draw from the grid by night.
How that is credited depends on your utility. Some programs credit exports at a high rate, and others pay much less. Our example assumes credits are capped at a year of grid purchases, with a yearly true-up. Read more in our guides on net metering vs. net billing, daytime electricity use and time-of-use rates.
If you can charge at midday or on weekends at home, you use more solar directly. If you cannot, ask your utility how night charging is priced.
Check your own numbers
Costs and rules vary a lot, so treat these figures as a starting point.
- Price per watt: Berkeley Lab reports a median installed price of $4.0 per watt for host-owned residential systems installed in 2024. Cash-purchased systems had a median of $3.5 per watt and loan-financed systems $4.7 per watt. Our example uses $3500 per kW, which equals $3.5 per watt. See our guide on cost per watt and payback.
- Incentives: The 30% federal Residential Clean Energy Credit (Section 25D) is not available for property placed in service after December 31, 2025, according to the IRS. Our math assumes no incentives. Check DSIRE for state and utility programs.
- Charging costs: Home charging costs differ by state. See our home EV charging cost guide.
- Local prices: Compare your rate with your state on our electricity prices page.
Practical next steps
- Estimate your car's yearly kWh. Use the 3500 kWh assumption only if you have nothing better.
- Add it to your current yearly use from your bills.
- Run both totals in our solar calculator to see how size and payback change.
- Ask installers to quote with and without the car, and compare the price per watt.
- Ask your utility how exports are credited and whether it has an EV rate.
Bottom line
An electric car pushes your yearly kWh up, so a right-sized solar system gets larger and costs more. In our example homes, payback stayed close to the same, and year-1 savings rose. Your result will depend on your utility, your charging habits, and your quote. Use the solar calculator with your own bills, and read our methodology to see how we do the math.
Sources
Get new articles by email
New articles and the monthly electricity price update. Unsubscribe anytime.
See our privacy policy.