Off-grid systems must be completely self-sufficient — the battery bank is the heart of the system. This guide covers the complete design methodology from load analysis to component selection.
Off-Grid System Architecture
- Solar panels: Charge batteries via MPPT charge controller
- Battery bank: Store all solar energy for nighttime and cloudy days
- Inverter: Convert DC battery power to AC for household loads
- Backup generator: Optional — for extended cloudy periods
The Critical Rule: Sizing for Worst Case
Never size an off-grid system for average conditions. Always design for the worst month of the year — typically December/January in the northern hemisphere or monsoon season in tropical regions.
Design for 3 consecutive cloudy days minimum.
Battery Bank Design
Bank Wh = Daily Load Wh x 3 (days autonomy) x 1.2 (safety margin)
For the example of 3,000Wh/day:
Bank = 3000 x 3 x 1.2 = 10,800Wh
At 48V: 10,800 / 48 = 225Ah rated
Use 4x CHISEN OPzV2-300 (2V 300Ah) = 48V 300Ah (allows 1.9 days at 100% DoD, or comfortable 1.5 days at 80% DoD)
With 3 cloudy days: requires 10,800Wh. Battery available: 48 x 300 x 0.80 = 11,520Wh — meets requirement with 1.07x margin
Generator Sizing for Backup
- Generator should recharge battery bank AND run loads simultaneously
- Minimum: 2x daily load in 4 hours of generator runtime
- Recommended generator: 2–3x inverter rated power
- For 5kW inverter: 10–15kVA generator
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