Solar System Size for Home EV Charging

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297 kWh/monthEV charging in the worked example

1,197 kWh/monthhome plus EV total

28 x 400W11.2 kW rounded array

Step 1: estimate EV charging energy

EV kWh/month = daily miles x kWh/mile x 30 x charging-loss factor

Worked example: 30 miles/day x 0.30 kWh/mile x 30 days x 1.10 = 297 kWh/month. Replace 0.30 with the vehicle's observed wall-to-wheel energy where available; weather, speed, tires, towing, and cabin heating or cooling change real consumption.

Step 2: add home use and size solar

required kW = (home kWh + EV kWh) x 12 / (365 x sun hours x 0.80)

Worked example: (900 + 297) x 12 / (365 x 4.5 x 0.80) = 10.93 kW. Dividing by 0.40 kW gives 27.3 panels, rounded up to 28 x 400W panels. Installed DC capacity is 11.2 kW and module surface is about 524 sq ft. At the calculator's 75% usable-roof assumption, the gross roof check starts near 699 sq ft.

EV load sensitivity

Driving pattern	EV assumptions	Added monthly use	Added solar at 4.5 sun hours
15 miles/day	0.30 kWh/mile, 10% loss	149 kWh	About 1.36 kW
30 miles/day	0.30 kWh/mile, 10% loss	297 kWh	About 2.71 kW
50 miles/day	0.30 kWh/mile, 10% loss	495 kWh	About 4.52 kW

Country and regional parameters to check

United States: compare home utility interval data, EV tariff or time-of-use rate, net metering, roof fit, and seasonal driving.
Australia: check daytime charging potential, export limits, controlled loads, inverter limits, and high-temperature production.
United Kingdom: check off-peak EV tariffs, winter driving efficiency, seasonal solar yield, export terms, and roof orientation.

Error boundary: annual solar energy does not ensure that the car charges directly from solar at night. Charging time, grid import/export rules, battery storage, charger power, household demand, and seasonal output determine actual grid interaction and savings.

Check roof fit, savings, and the next project step

The prefilled roof-fit link represents the 28-panel example. After calculating, use the built-in next-step links and Solar Project Summary to move into Savings or Battery Sizing.

Check need vs roof fit Estimate 11.2 kW savings Consider battery timing Review the assumptions

Related planning evidence

Usage referenceCompare monthly kWh and panel count

System comparisonCompare 5 kW and 10 kW

Backup loadSize an 8-hour outage battery

Last reviewed July 18, 2026. Planning estimate only; vehicle, tariff, price, and installation outcomes are not promised.