Charging an EV with Solar Panels — Is It Free?

Start with annual kWh, not battery size. An EV using 12,000 miles per year at 3.5 miles per kWh (near the US midpoint for common models) draws 3,429 kWh from the wall after accounting for 8% charging losses. At 1,500 kWh/kW-year of solar production (NREL national average for residential systems), that requires a 2.3 kW solar addition — roughly 6-7 panels at 400W each. More efficient EVs (4+ mi/kWh) need closer to 1.9 kW; larger trucks and SUVs (2 mi/kWh) need 3.5+ kW. These are the extra panels beyond what the home already needs.

Most US drivers charge overnight on Level 2 — which means every kWh going into the car came from the grid, not directly from solar. The solar panels produced power during the day and either offset daytime household load or were exported. Whether that counts as "solar charging" depends on net metering: if the utility credits exports at the full retail rate, the economics are equivalent. If exports are credited at avoided cost ($0.03-0.05/kWh instead of $0.16+/kWh), the timing gap costs real money. The gap is widest in California under NEM 3.0, where daytime exports earn about $0.05/kWh but home charging costs $0.30+/kWh at peak.

A home battery stores daytime solar production and discharges it during evening charging sessions. This makes timing irrelevant — the car charges from stored solar regardless of when the panels produce. The cost to close the timing gap is the battery: typically $800-1,200/kWh of usable capacity installed. At that cost, the battery payback from avoiding export-credit losses must be calculated separately from EV savings. In strong net-metering states, a battery may add cost without adding much benefit. In NEM 3.0 California or other weak-export states, it can change the economics substantially.

Adding a car to an existing solar system is a different calculation than sizing a new system that includes the car. For an existing system: add the car's annual kWh to the home's current consumption and resize using PVWatts for the location. For a new combined system: size for home + car together to capture incentives on a single installation. The federal residential clean energy credit (26C) applies to solar installation costs; EV charging equipment may qualify under 30C. Run both calculations with the EV Charging Cost Calculator and Solar ROI Calculator before sizing.

No. Solar has an upfront cost — typically $2.50-3.50/W installed in 2025 — and payback takes years. What solar can do is drive the effective per-kWh cost of EV charging toward $0.03-0.06/kWh over the system lifetime, compared to $0.12-0.42/kWh from the grid. That is a genuine long-term savings, but it requires a working solar system, realistic production assumptions, and an honest accounting of when the car actually charges versus when the panels produce.