Solar System Off-Grid Calculator
Size a complete off-grid system: panels, batteries, inverter, and controller
How to Use This Calculator
- Enter your total daily energy consumption in kWh/day (sum up appliance watt-hours; the U.S. off-grid home average is 15–30 kWh/day).
- Input your local peak sun hours (use 4.5 as a national average).
- Choose days of autonomy — how long the battery bank should power you with no sun (2 days is typical).
- Select your battery bank voltage (48V for systems over 1.5 kW) and chemistry DoD.
- Enter your peak simultaneous AC load in watts (the largest combined draw at any moment).
- Read the recommended panel array, battery bank, charge controller, and inverter size.
Off-Grid Sizing Formulas
Panel Array (kW) = Daily kWh ÷ (Peak Sun Hours × 0.75 system derate)
Battery Bank (kWh) = Daily kWh × Days of Autonomy ÷ (DoD × 0.95 inverter eff.)
Battery Bank (Ah) = Bank kWh × 1000 ÷ Bank Voltage
Charge Controller (A) = Array Watts ÷ Bank Voltage × 1.25
Inverter (kW) = Peak AC Load × 1.25
| Daily Use | Array | Battery (48V LiFePO4, 2-day) | Controller | Inverter |
|---|---|---|---|---|
| 5 kWh/day | 1.5 kW | 11 kWh / 230 Ah | 40A MPPT | 3 kW |
| 15 kWh/day | 4.4 kW | 33 kWh / 680 Ah | 120A MPPT | 6 kW |
| 30 kWh/day | 8.9 kW | 66 kWh / 1,370 Ah | 240A MPPT | 10 kW |
| 50 kWh/day | 14.8 kW | 110 kWh / 2,290 Ah | 3×80A MPPT | 15 kW |
Complete Off-Grid Systems
Frequently Asked Questions
What is system derate and why 0.75?
Derate accounts for real-world losses — inverter efficiency, wiring, soiling, temperature, and battery round-trip. Off-grid systems typically deliver ~75% of nameplate panel wattage as usable AC energy.
How many days of autonomy do I need?
2–3 days is standard for LiFePO4 systems. In cloudy or winter climates, size for 3 days and consider a backup generator. Lead-acid banks should avoid deep cycling, so add more capacity.
Can I add a generator for backup?
Yes. Many off-grid inverters (hybrid) auto-start a generator when the battery drops below a threshold, extending autonomy through long cloudy periods.