Enter your location, seasonal loads and how many days of storage you want to get a preliminary solar array, battery bank and backup generator size.
Off-grid planning calculator
Planning a cabin or home without a grid connection? Enter your location and what you need to run in summer and winter. We size the solar array for your darkest month, the battery bank for the cloudy days you want to ride through, and an optional backup generator.
Assumptions and limits
- Solar production: NLR PVWatts v8 for your location, month by month, 14% losses. A ZIP uses the center of its 3-digit ZIP area (U.S. Census Bureau Gazetteer and Geocoder).
- Appliance watts: Honda wattage guide, Champion wattage chart, ENERGY STAR product data (fridge 363 kWh/yr, upright freezer 438 kWh/yr, TV 85 W, ceiling fan 30 W, 8,000 Btu window AC 533 W), ResMed AirSense 11 user guide (CPAP 56 W typical, 73 W peak). LED bulb 9 W, router + modem 20 W and laptop 65 W are typical label values. Hours per day are examples: change them to match your home. Your appliance labels beat any chart.
- Seasons: summer hours apply May–October, winter hours November–April. Panels face true south.
- Storage losses: we assume all solar energy passes through the battery and keep 85% of it (NREL’s NREL Annual Technology Baseline, 85% round trip). Conservative; some energy is used directly.
- Array size without a generator: big enough for the worst month. With a generator: big enough for the third-worst month; the generator covers the two darkest months (our design choice to keep the array affordable).
- Battery bank: worst daily load × days of autonomy ÷ usable depth ÷ 92% (inverter side, half of the 85% round trip). Usable depth: LiFePO4 80% (makers rate cycle life at 80% depth; some allow 90%), lead-acid 50% (Trojan Battery recommends 50% or less).
- Generator: at least the running load plus the biggest motor start, and enough to charge the bank at about 0.2 C (one fifth of its kWh per hour, our assumption; check the battery maker). Running hours a year = monthly shortfall ÷ charging power; real hours run higher in long cloudy spells.
- Wind and micro-hydro: wind is often strongest in winter when sun is weakest; small wind needs an average of about 9 mph or more (DOE Small Wind Guidebook). A stream that runs all year and drops in height can run micro-hydro day and night.
- Not included: wire sizing, charge controller and inverter selection, cold-weather battery heating, code and permits.
- This is an estimate, not a design. A licensed installer must confirm sizing, wiring and permits.
Learn more in our Off grid guide, or see all calculators.