Free off-grid solar calculator & system simulator. Size solar panels, LiFePO4 battery bank, inverter, MPPT, and wire gauge in one click.
ℹ️ Note: Based on 82% net PV system efficiency and 15% thermal safety derating per NREL PVWatts standards.
Designing a standalone off-grid solar energy system requires strict mathematical balance between daily electrical consumption, local solar irradiance, battery autonomy reserve, pure sine wave inverter surge capacity, and conductor voltage drop.
Unlike grid-tied systems where utility power provides an infinite buffer, an off-grid electrical system is a closed microgrid. Underestimating winter solar deficits results in premature battery sulfation or lithium low-voltage cutoffs. Overestimating components inflates capital costs unnecessarily.
Our engineering calculation engine is informed by design principles from National Electrical Code (NEC 2023) Articles 690 & 706 and IEEE 1568 stand-alone photovoltaic design standards, computing exact PV array wattage, battery Amp-Hour storage, and conductor sizes in a unified workflow.
A modern off-grid cabin in the American Sunbelt consumes 5,000 Watt-hours (5 kWh) daily, operating a refrigerator, Starlink satellite terminal, LED lighting, and intermittent kitchen appliances.
PV Watts = (5,000 Wh) / (4.5 PSH × 0.82 Yield) × 1.15 Safety = 1,558 Watts
Dividing daily energy by 4.5 peak sun hours and accounting for 18% balance-of-system losses yields a minimum 1,558W array, met by four 400W commercial monocrystalline panels (1,600W total).
Storage kWh = (5,000 Wh × 2 Days Autonomy) / 0.80 DOD = 12,500 Wh (12.5 kWh)
Two days of reserve autonomy during heavy cloud cover requires 12.5 kWh of gross storage. At 24V DC, this equals 520 Amp-Hours (Ah), achieved via two 24V 200Ah + one 24V 100Ah LiFePO4 batteries in parallel.
Continuous Inverter = 1,850W Continuous Peak × 1.25 = 2,312W (Select 3,000W Inverter)
A 3,000W continuous / 6,000W surge pure sine wave inverter safely handles compressor inductive motor startup spikes without tripping overcurrent protection.
✅ Engineering Sizing Result: This balanced 5 kWh/day blueprint provides dependable year-round power with zero generator runtime in spring/summer and predictable 2-day autonomy during winter storms.
Aggregates all continuous and cyclic electrical loads over a standard 24-hour cycle.
Accounts for dirt/soiling (3%), thermal derating (8-10%), wiring resistance (2%), and inverter conversion losses (93% efficiency).
Protects battery longevity by restricting maximum discharge to 80% for LiFePO4 Lithium or 50% for Lead-Acid AGM.
| Daily Load (kWh) | System Bus Voltage | Recommended Solar Array | Battery Capacity (LiFePO4) | Target System Application |
|---|---|---|---|---|
| 1 kWh / day | 12V DC | 400W Array (1x 400W) | 208 Ah @ 12V (2.5 kWh, 2 Days) | RVs, Camper Vans, Small Sheds |
| 5 kWh / day | 24V DC | 1,600W Array (4x 400W) | 521 Ah @ 24V (12.5 kWh, 2 Days) | Off-Grid Cabins, Tiny Homes |
| 10 kWh / day | 48V DC | 3,200W Array (8x 400W) | 521 Ah @ 48V (25 kWh, 2 Days) | Full-Time Residential Homes |
| 20 kWh / day | 48V DC | 6,400W Array (16x 400W) | 1,042 Ah @ 48V (50 kWh, 2 Days) | Large Homesteads & Workshops |
Always start with your daily electrical consumption in Watt-hours (Wh) or Kilowatt-hours (kWh). Every other component—solar panel array, battery bank, inverter, charge controller, and wire gauge—is directly scaled from your load requirements.
Use 12V for portable or vehicle applications under 1,000W. Use 24V for small cabins and systems between 1,000W and 3,000W. Use 48V for systems exceeding 3,000W; higher voltage cuts conductor current by 75%, allowing much thinner wire and dramatically reducing resistive heat loss.
Most off-grid solar engineers recommend 2 days of autonomy for areas with reliable sunshine (Sunbelt, desert climates) and 3 to 4 days for northern, forested, or frequently overcast regions.
Itemize daily appliance wattages and identify continuous vs peak surge watts.
Next StepDetermine PV array wattage based on local peak sun hours.
Next StepCompute Amp-Hours and battery bank series/parallel wiring.
