Calculate how many solar panels you need to charge an EV from your daily miles, using typical EV efficiency, panel size and sun hours or your own values.
Solar Panels to Charge an EV Formula
The calculator sizes a solar array in three steps. First it works out how much energy the system must generate each day to charge the car, including charging losses:
Battery basis: Eev = (M * Em) / Ce Wall / EPA-label basis: Eev = M * Em
Next it finds how much energy a single panel produces on an average day, after system losses:
Ep = (Pw / 1000) * Sh * PR
Then it divides the two and rounds up to a whole number of panels, and converts that to an array size in kilowatts:
N = ceil( Eev / Ep ) A = N * Pw / 1000
Variables:
- Eev is the daily solar energy the system must generate to charge the EV, in kWh
- M is the distance driven per day, in miles or km (weekly and yearly amounts are converted to a daily average)
- Em is vehicle energy per unit distance on the selected basis, converted consistently to kWh/mile. EPA label consumption is wall/outlet energy, including charging losses; choose wall basis for those figures. Battery-reported energy instead uses the charging-efficiency adjustment.
- Ce is the charging efficiency as a decimal, such as 0.90 for 90 percent
- Ep is the energy one panel produces per day, in kWh
- Pw is the panel wattage, in watts
- Sh is average daily irradiation on the panel plane divided by 1 kW/m², in equivalent peak sun hours. Use a location, orientation and period-specific estimate; it is not daylight duration.
- PR is a simplified combined PV-to-AC performance factor, equal to 1 minus entered PV losses (0.80 for the illustrative 20 percent setting). It excludes EV charging losses and is not the PVWatts system-loss default.
- N is the number of panels, rounded up to the next whole panel
- A is the total array size, in kW
Enter driving distance and period, vehicle efficiency and its battery or wall measurement basis, panel wattage, and peak sun hours. Solar and charging losses are optional: blanks use 20 percent combined PV losses and 90 percent charging efficiency; charging efficiency applies only to battery basis. Calculate shows whole panels, rated array kW and average daily AC energy. Zero driving requires zero panels. Your last successful inputs are saved in this browser; other scripts on this site may access them, and Reset clears this calculator’s saved data.
Panels Needed by Daily Miles
This table shows the panels and array size for common daily driving distances, assuming battery-side 3.5 mi/kWh efficiency, 400 W panels, 4.5 peak sun hours, a performance ratio of 0.80, and 90 percent charging efficiency. Use it as a quick reference before you enter your own numbers.
| Daily driving | Daily kWh needed | Panels needed | Array size |
|---|---|---|---|
| 20 miles/day | 6.35 kWh | 5 | 2.0 kW |
| 30 miles/day | 9.52 kWh | 7 | 2.8 kW |
| 40 miles/day | 12.70 kWh | 9 | 3.6 kW |
| 50 miles/day | 15.87 kWh | 12 | 4.8 kW |
Fewer panels are needed with more equivalent sun hours; lower sun or poorer vehicle efficiency needs more panels. This is an average energy-offset estimate, not hourly or off-grid design. Seasonal weather, shading, roof area, inverter/charger limits and charging times need separate assessment. PVWatts models production in more detail; do not apply these PV losses again to an already net AC generation estimate.
Example Problems
Example 1: A typical commuter.
You drive 30 miles per day in an EV with battery-side efficiency of 3.5 mi/kWh, using 400 W panels with 4.5 peak sun hours, 20 percent system losses, and 90 percent charging efficiency.
Energy per mile is 1 / 3.5 = 0.286 kWh, so the car uses about 30 * 0.286 = 8.57 kWh at the battery. Dividing by 0.90 charging efficiency gives Eev = 9.52 kWh of solar to generate. Each panel makes Ep = (400 / 1000) * 4.5 * 0.80 = 1.44 kWh per day. Then N = ceil(9.52 / 1.44) = ceil(6.61) = 7 panels, an array of 7 * 400 / 1000 = 2.8 kW.
Example 2: A higher-mileage driver with larger weekly distance.
You drive 250 miles per week (about 35.7 miles per day) in an EV with battery-side efficiency of 3.0 mi/kWh, using 350 W panels with 5 peak sun hours and the same losses and charging efficiency.
Energy per mile is 1 / 3.0 = 0.333 kWh, so daily use is 35.7 * 0.333 = 11.90 kWh at the battery, and Eev = 11.90 / 0.90 = 13.23 kWh. Each panel makes Ep = (350 / 1000) * 5 * 0.80 = 1.40 kWh. Then N = ceil(13.23 / 1.40) = ceil(9.45) = 10 panels, an array of 10 * 350 / 1000 = 3.5 kW.
Frequently Asked Questions
How many solar panels does it take to charge an EV?
For an average driver covering about 30 miles a day in a car with battery-side efficiency of 3.5 mi/kWh, roughly 7 standard 400 W panels, or about a 2.8 kW array, cover the charging over a year in a location with 4.5 peak sun hours. The exact number depends on how far you drive, how efficient the car is, your panel wattage, and how much sun your roof gets, which is why the calculator lets you enter all of those.
Can I charge my EV directly from solar?
You can, but panels only produce while the sun is up, so direct daytime charging works best if the car is home during the day or you have a charger that follows the available solar output. Most owners instead let the panels feed the home and grid during the day and charge the car whenever it is parked, using net metering or a home battery to bridge the timing gap.
Do I need a battery to charge my EV with solar?
No. A grid-tied system without a battery can still cover your driving on an annual basis by exporting surplus solar during the day and pulling power back at night, as long as your utility offers net metering. A home battery adds resilience and lets you charge on stored solar after dark, but it is not required for the panel counts this calculator produces.
