Off-grid sizing workflow
How to size an off-grid solar system
Size the loads first, then storage, then solar. Starting with a panel kit or inverter rating usually leaves the daily energy question unanswered.
1. Build a daily load total
For every appliance, multiply watts by quantity and hours used per day. Add the rows in watt-hours. For cycling loads such as refrigerators, measured daily energy is better than nameplate power.
daily Wh = Σ(watts × quantity × hours)2. Choose autonomy and usable battery limits
Autonomy is the number of days the battery must cover without useful charging. Divide the delivered energy by depth of discharge, battery efficiency, and inverter efficiency for AC loads. Keep reserve explicit.
3. Convert the energy target into a real battery bank
Choose a nominal system voltage, convert required Wh to Ah, and round up to whole matching modules. Recalculate installed capacity from the final series-parallel layout.
4. Size solar from the daily load
Divide daily energy by peak sun hours and system efficiency. Then divide by panel watts and round upward. Check winter and poor-weather assumptions separately rather than hiding them in an annual average.
array W = daily Wh ÷ (peak sun hours × efficiency)5. Check the parts the calculators do not design
Verify controller voltage and current windows, cold-weather Voc, inverter surge, charging limits, cables, protection, grounding, structure, and local rules. The current estimate is not an equipment approval.
Use the linked calculators
Start with the load and backup calculator, confirm storage in the battery calculator, then size generation with the solar panel calculator.