Solar EV Charging Calculator

This calculator sizes a home solar system to offset EV charging electricity and estimates the resulting cost payback. Daily kWh Needed is Daily Miles Driven divided by EV Efficiency (miles per kWh) -- the actual electricity your EV consumes each day. Each solar panel is assumed to produce Panel Wattage x Peak Sun Hours x 80% system efficiency (accounting for inverter, wiring, and soiling losses) per day, in kWh; Panels Needed is the number of panels required for that daily production to cover your EV's daily kWh needs, rounded up to a whole panel. No single input dominates Panels Needed: the formula is exactly unit-elastic in all four, so a 1% change in Daily Miles Driven, EV Efficiency, Peak Sun Hours or Panel Wattage each moves the answer by the same 1% before rounding up to a whole panel.

Daily Miles Driven and the three others simply push in opposite directions -- more driving needs more panels, while a more efficient car, a sunnier site or a higher-wattage panel each need fewer. Annual Savings values the smaller of your solar production or EV consumption at the Electricity Rate you enter, so an oversized system (producing more than the EV uses) does not inflate the reported savings. That rate is the single biggest lever on Payback Period -- residential rates run from about 11 cents to over 40 cents per kWh depending on the state, a spread that moves payback on the same system by roughly a factor of four -- so take it off a recent bill rather than leaving the default. Payback Period is calculated on the full, un-subsidized system cost at the Installed Cost per watt you enter, defaulting to $3.50/W because the 1-3 kW arrays this calculator sizes carry fixed permitting and inverter costs over far fewer watts than the 7-10 kW systems whole-market averages are drawn from: the federal 30% residential solar tax credit (IRC Section 25D) was terminated by Section 70506 of the One Big Beautiful Bill Act (Public Law 119-21) for expenditures made after December 31, 2025, so there is no federal credit built into this estimate -- a reader with a state or utility rebate should factor that in separately when judging payback.