Find out exactly how much larger your solar system needs to be to charge your electric vehicle at home — for free.
Quick answer
An average EV driver covers 12,000 miles/year and uses 3,000–5,000 kWh of electricity to do it. That requires 2–4 extra kW of solar panels. Charging overnight with solar stored in a battery gives you maximum value from every kWh.
Reviewed 2026-07-26
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- Homeowners pressure-testing solar proposals before signing.
- Inputs needed
- electric usage, local rate, system size or quote assumptions
- Formula used
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- Source checked
- NREL PVWatts, DSIRE, public utility tariffs
Quick Answer
An average EV driver covers 12,000 miles/year and uses 3,000–5,000 kWh of electricity to do it. That requires 2–4 extra kW of solar panels. Charging overnight with solar stored in a battery gives you maximum value from every kWh.
Source: Wattcrunch methodology and cited primary data
Solar + EV is the most powerful combination in home energy
An electric vehicle owner who pairs their car with rooftop solar effectively locks in a fuel price of near-zero for the life of the panels. The average US driver spends $1,400–$2,200/year on gas. A solar-charged EV can cut that to under $100 in electricity costs by year 10. Over a 25-year panel lifespan, the math is transformative.
Why EV owners need to re-size their solar system
Most solar installers size systems for your historical electricity usage — which doesn't include the EV you're about to buy, or bought last year. Adding an EV typically increases a home's electricity consumption by 30–50%. A system sized without accounting for EV charging will leave you relying on grid power for most of your driving, missing the biggest single savings opportunity in the solar+EV combo.
EV charging and time-of-use rates
If your utility has TOU pricing, when you charge matters as much as how much solar you have. Charging at midnight on an off-peak rate ($0.10/kWh) is far cheaper than charging at 7 pm on a peak rate ($0.40/kWh). Solar-charged EVs at midday is the holy grail — but even without midday charging, pairing solar export credits with off-peak overnight charging dramatically reduces your effective fuel cost.
Sources behind this estimate
Wattcrunch combines user inputs with published solar-production, electricity-market, incentive, and tariff information. Use the primary references below to understand what the model can estimate and what still needs confirmation for your property.
Utility export rates, eligibility rules, and installer pricing can change. Confirm the applicable tariff, interconnection requirements, and tax treatment before making a purchase decision.
Frequently asked questions
How many solar panels do I need to charge my EV?+
The exact number depends on how many miles you drive. A typical US driver covers 12,000 miles/year. In a Tesla Model Y at 3.5 mi/kWh, that is 3,430 kWh of home charging. At 4.5 peak sun hours and 400W panels, you need about 2.1 kW or roughly 6 additional panels to cover that load. Our calculator does this math for every major EV model.
Is charging my EV from solar actually free?+
Once the panels pay for themselves (typically 7–10 years on the EV-sized portion), yes — the electricity is free for the remaining 15+ years of panel life. In year one, the cost per mile is the solar system cost amortized over its lifetime, which typically works out to $0.01–$0.03/mile, vs $0.04–$0.06/mile from the grid.
What is the best time to charge an EV with solar?+
Midday, typically 10 am–2 pm, when solar output is highest. If you work from home or have a Level 1 charger (1.4 kW), you can passively charge during peak solar hours. With a smart charger (JuiceBox, Chargepoint, Tesla Wall Connector), you can set a solar-first schedule automatically.
Does adding an EV change my solar payback period?+
Almost always yes, in a good way. The additional panels sized for EV charging have a faster payback than your base system in many cases, because you are displacing expensive gasoline (or high-rate grid electricity). The math is most compelling if you were previously spending $1,500+/yr on gas.
Can I use net metering credits to offset EV charging at night?+
Under full retail net metering (many states), yes — your midday surplus earns credits that offset your overnight EV charging dollar-for-dollar. Under net billing (California NEM 3.0 and others), exports earn less than imports cost, making a battery more attractive for EV owners.