Quick answer: start with 5,100 W of solar
An EV is usually the largest daily load an off-grid home ever adds. At 1,900 W for 6 hours the charger uses 11,400 Wh, so the system has to collect about 15,200 Wh a day, roughly a 5,100 W array for the car alone. The cheapest way to supply it is to charge while the sun is up, straight from the array, so the house battery never has to store a day of driving.
Planning result
At 200 W per module, the array target is 26 panels. That count assumes four peak-sun-hours, 75% end-to-end solar yield, 90% conversion efficiency, and a 20% planning margin. Winter is the hard case twice over: fewer sun-hours, and the car uses more energy per mile in the cold because it heats its cabin and battery.
How a Level 1 EV charger actually uses power
Planning case: a Level 1 cord set on a 120 V outlet drawing about 1,900 W, the charging power the U.S. Department of Energy's Alternative Fuels Data Center uses for Level 1, for 6 hours a day. At the AFDC's estimate of about 5 miles of range per hour of Level 1 charging, that is roughly 30 miles a day from about 11.4 kWh at the wall. Many cord sets on a 15 A outlet run nearer 12 A, about 1.4 kW, which this case covers with margin.
A charging EV is a flat, constant load. The cord set holds its current setting until the car's battery is nearly full, then the car tapers the current for the last few percent. There is no thermostat or compressor cycling, so the duty factor is 100% for the scheduled hours. Daily energy is set by the miles you drive, not by the charger: halve the driving and you halve the watt-hours, but the charger still pulls the same 1,900 W while it runs.
Load calculation from running watts and duty cycle
The appliance-class estimate is 1,900 W running for 6 h/day at a 100% duty cycle, an average of about 1,900 W across those hours:
Then losses and reserve raise the energy the system must collect to about 15,200 Wh/day.
Typical manufacturer nameplate/manual range for the Level 1 EV charger class, triangulated with U.S. Department of Energy Alternative Fuels Data Center: Electric Vehicle Charging Stations and ENERGY STAR: Electric Vehicle Chargers, then reduced to a conservative planning midpoint; this is not a product specification. Verify the exact unit's nameplate and manual before sizing.
The car is the best meter. Most EVs and many cord sets report the kWh added in each session; log a typical week and divide by the days you drove. A plug-in watt meter is a poor fit for hours of continuous high current, so read the car or charger instead.
Solar and battery sizing table
| Design item | Planning value | Basis |
|---|---|---|
| Appliance energy | 11,400 Wh/day | Running W × hours × duty cycle |
| Solar collection target | 5,100 W | 4 peak-sun-hours, 75% yield, 20% margin |
| 200 W panel count | 26 | Rounded up; real modules must satisfy controller voltage/current limits |
| One-day battery allowance | 19,000 Wh | 90% conversion efficiency, 80% LiFePO4 usable fraction, 20% margin |
| 12.8 V LiFePO4 equivalent | 1,485 Ah | Nominal planning conversion |
| 25.6 V LiFePO4 equivalent | 745 Ah | Nominal planning conversion |
Because the car is itself a large battery, a house battery sized for a whole day of charging (19,000 Wh here) is usually the wrong design. Size house storage for the house, schedule EV charging into the solar window, and use the one-day figure only if the car truly must charge after dark.
Build the closest passing wiring-diagram preset
The Level 1 EV Charger Planning System preset is an engine-passing starting point whose array, battery bank, continuous inverter rating, and surge rating each meet or exceed this page's stated planning allowances. Adjust it only from measured load data and verified equipment limits.
Inverter and startup current
Use at least 2,400 W continuous with 2,400 W surge for this planning case. A Level 1 cord set has no motor to start: after the car and charger handshake, the current ramps up to its setting, so the surge allowance is the same as the continuous one. What the inverter needs is a continuous rating that carries 1,900 W for hours without overheating, plus headroom for any house loads that run at the same time.
Because this load draws its full power for long stretches rather than for a moment, the battery-to-inverter cable carries heavy current continuously. A run that is too long or too small wastes energy as heat and can push the inverter to its low-voltage cutoff late in the day, even with energy left in the battery, so use the diagram machine's real run length and keep every fuse within the equipment and conductor limits. The 2,000 W peak estimate is a planning figure, not the manual's rating.
The common mistake
Ways to cut the load
- Charge between mid-morning and mid-afternoon so the array, not the battery, supplies most of the 11,400 Wh.
- Lower the charge current in the car's settings on cloudy days so the house keeps its own reserve.
- Set the car's charge limit to what tomorrow's driving needs instead of 100% every day.
- Track miles per kWh in summer and in winter; the winter figure is the one to size the array for. ENERGY STAR puts Level 1 at 2 to 5 miles of range per hour, so your own car's figure matters.
What to verify before buying equipment
- The exact running watts, startup current, voltage, frequency, and required circuit from the appliance label and manual.
- Actual watt-hours over a representative day; seasonal heating or cooling loads need a design-day measurement.
- Local peak-sun-hours for the worst operating season, plus shade and array orientation.
- Controller maximum input voltage at the coldest expected temperature and maximum output current.
- Battery discharge current, series/parallel permission, terminal torque, low-temperature controls, and overcurrent protection.
- Conductor ampacity, voltage drop, terminal temperature ratings, disconnecting means, grounding, local amendments, and inspection requirements.
For a whole-system load list, use the load and appliance calculator. For the system context around this appliance, continue to the Garage and workshop solar guide.
Frequently asked questions
How much solar do I need for a Level 1 EV charger?
For the planning case on this page (about 1.9 kW at 120 V for six hours a day), allow about 5,100 watts of solar at four peak-sun-hours per day. That covers an estimated 11,400 Wh daily load plus conversion, temperature, and recharge margin. If you drive half as far, the energy and the array both scale down by half, but the charger's 1,900 W draw while charging stays the same.
What size inverter should I use for a Level 1 EV charger?
Plan on at least 2,400 W continuous and 2,400 W surge. A Level 1 charge is a long continuous load, so choose an inverter whose continuous rating, not its surge rating, covers the charger plus everything else running at the same time.
What battery size keeps a Level 1 EV charger running for one day?
The one-day planning allowance is about 19,000 Wh nominal usable design capacity, roughly 1,485 Ah at 12.8 V or 745 Ah at 25.6 V for LiFePO4. In practice most off-grid EV owners charge during sun-hours instead, so the house battery only has to cover the house.