How Many Solar Panels Do You Need to Charge an Electric Car?
Work out how many solar panels your EV may need. Start with your driving and charging energy, then check local solar output, winter production and roof space.
Your panel count depends on your yearly driving and the solar energy your roof can produce. Start with your yearly home-charging needs. Then use a local solar estimate to work out the system size and panel count.
This gives you a yearly energy estimate. It won't promise direct solar charging every day, a zero bill or power during an outage. Use the home EV charging guide for the charger and the home solar guide for the roof and utility questions.
Work out your yearly home-charging needs
Start with the yearly miles you'll charge for at home. Leave out miles covered by charging at work or in public. Allow for changes you expect in your driving. For two cars, work out each one's needs before adding them together.
Energy is measured in kilowatt-hours (kWh). Check where your energy-use figure is measured. For battery energy, multiply miles by kWh per mile and divide by charging efficiency. If the figure already measures electricity from the wall, use it as it is. You can also use a suitable year's measured home-charging total. The EPA's testing guide explains how its outlet-based figures include AC charging losses. Don't add those losses again.
Let's use a made-up example: 12,000 miles charged at home each year, 0.30 battery kWh per mile and 90% charging efficiency. The car uses 3,600 kWh from the battery. Replacing it takes 4,000 kWh from the wall each year. These are example figures, not test results or an average for U.S. drivers.
Get a solar estimate for your roof
A panel's watt rating tells you its direct-current (DC) power under set test conditions. It doesn't tell you how much alternating-current (AC) electricity your home will get over a year. Location, roof direction, angle, shade, weather, the inverter and energy losses all affect that amount.
Use a tool such as the PVWatts calculator, or ask an installer for a site estimate. Get the yearly and monthly AC output, the panels' total DC rating and the assumed losses. Ask how shade was checked. The figures are estimates, not guaranteed production.
Ask how many AC kWh each installed DC kW is expected to produce in a year. Here's a made-up figure: 1,350 kWh per kW per year. That means a 1-kW DC system is expected to produce 1,350 AC kWh in this example. If that output already allows for solar-system losses, don't subtract a second allowance.
Work out the panel count
Solar-system size in DC kW = yearly EV charging energy at the wall ÷ yearly AC kWh produced per DC kW. Next, divide that system size by one panel's DC kW rating. Round up to a whole panel. The table shows each step.
| Example step | Calculation | Result |
|---|---|---|
| Electricity for charging, measured at the wall | 12,000 miles × 0.30 battery kWh/mile ÷ 0.90 | 4,000 kWh/year |
| Required solar-system size | 4,000 ÷ 1,350 | About 2.96 kW DC |
| First estimate using 400-watt panels | 2.96 ÷ 0.40, rounded up | 8 modules |
| Total panel rating | 8 × 0.40 | 3.2 kW DC |
| Estimated yearly AC electricity | 3.2 × 1,350 | 4,320 kWh/year |
Rounding up gives an extra 320 kWh in this example. That isn't a promise of spare power in bad weather, or proof the panels fit your roof. The layout, panel sizes, electrical design and utility limits can all change the final plan.
Now change the solar estimate. Keep the same 4,000-kWh target and 400-watt panels. A yearly output of 1,000 kWh per installed kW calls for ten panels. At 1,600, it calls for seven. These made-up figures show how the calculation works; they aren't recommendations for particular regions.
Check winter output and when you can charge
Enough solar energy over a full year may still leave you short in winter. Compare monthly production with your driving and energy use in each season. In cold weather, the panels may produce less while the car uses more.
Also think about when your car is home. If it's away on sunny days, you may send solar power to the grid and buy electricity to charge later. Charging directly from available solar needs compatible controls and time plugged in during production. A home battery adds cost and more energy losses. Don't add one just to make a yearly panel calculation look self-sufficient.
Check the prices for buying electricity and the credits for sending solar power to the grid. Our charging cost worksheet and net billing comparison explain those choices. Matching yearly kWh doesn't mean the bill will balance too.
Avoid counting the same energy twice
If your electricity records already include the EV, don't add its full yearly use again. The same applies to existing solar. If that production already supplies the house or earns credits, account for what changes when you use it for the car.
- New EV, existing household records: add only the extra electricity used to charge at home.
- EV already in the bills: find its share of the existing total.
- Existing solar: use records of production, electricity bought and power sent to the grid. The final bill alone may hide some energy use.
- Several upgrades: put the heat pump, EV and other changes into one household estimate.
Our heat-pump-and-EV solar sizing guide brings those household needs together. This page works out the car's share so you can add it to the wider plan.
Check roof space and backup power separately
Have an installer check the roof's condition, space, shade, structure and electrical needs. They should also confirm permits and utility approvals. An eight-panel estimate isn't a finished roof design.
🛑 Roof and electrical safety: Don't climb onto the roof or change solar or charging wiring to check these figures. Make observations from the ground and have a professional assess the system.
Ordinary grid-connected solar normally stops supplying power during an outage. Read the solar outage guide before assuming it can charge your car when the grid is down. Powering the home from the car also needs approved equipment. The V2L, V2H and V2G guide explains those different jobs.
What to ask solar installers
- Write down yearly miles charged at home and where the energy-use figure is measured.
- Explain how charging losses are included, or use measured electricity from the wall.
- Ask for yearly and monthly AC output for your roof, with losses explained.
- Compare electricity bought, solar sent to the grid and any seasonal shortfalls.
- Ask the quote to separate normal charging, solar controls and outage backup.
Conclusion
Work out your yearly home-charging energy, then compare it with expected solar production and panel size. Before buying, check winter output, electricity prices, roof space and when you can plug in. Those details turn a rough panel count into a useful plan.
Read our Energy Efficiency guides for help with the rest of your solar and home upgrade plans.
Scott Harding
Scott is the main author of DIY Home Comfort. Learn more about the team and our approach on the About page.
