Designing an off-grid solar battery bank requires balancing competing priorities: enough capacity to meet daily energy needs, low enough Depth of Discharge to maximize cycle life, sufficient reserve for multi-day cloudy periods, and a budget that doesn’t break the project. Here is the complete design methodology.
Step 1: Calculate Daily Energy Requirement
List every electrical load and its daily energy consumption in Wh. Be honest and thorough — this is where most off-grid systems fail. Include lights, refrigeration, phone charging, water pump, inverter standby consumption, and any seasonal loads.
Step 2: Determine Required Capacity
Daily Ah requirement = Daily Wh consumption / System voltage / System efficiency factor (typically 0.85 for overall system losses).
Then size the battery bank: Battery Ah = Daily Ah requirement / Allowable DoD. For longest life, use 30% DoD. For moderate budget, 50% DoD is common.
Step 3: Size for Days of Autonomy
In areas with frequent cloudy weather, size the bank for 3-5 days of autonomy at the allowable DoD level. Multiply the daily Ah requirement by the number of backup days.
Step 4: Calculate Solar Recharging Requirement
The solar array must fully recharge the battery bank from its daily discharge AND have surplus to cover days of autonomy. A common rule: solar wattage = Daily Wh requirement x 1.3 / Peak sun hours x 0.8 (derating factor).
Step 5: Select Battery Chemistry and Voltage
- Small systems (<5kWh/day): 24V or 48V AGM system
- Medium systems (5-20kWh/day): 48V AGM or LFP
- Large systems (>20kWh/day): 48V LFP or higher voltage
For off-grid solar battery sizing support: sales@chisen.cn