Solar Battery Bank Sizing Calculator: Off-Grid and Hybrid Systems 2026

This guide provides a step-by-step battery bank sizing methodology used by professional solar engineers. Includes worksheets for both off-grid homes and hybrid grid-tie systems.

The Four Sizing Variables

1. Daily consumption (Wh): Total energy used per day from all appliances
2. System voltage: 12V, 24V, or 48V DC bus voltage
3. Depth of discharge: How much capacity you use each cycle
4. Days of autonomy: How many days the bank must supply power without solar input

Step 1: Calculate Daily Wh

Use an electricity meter or estimate from appliance nameplates:

• LED lighting (home, 10 x 10W, 5 hrs/day): 500Wh
• Refrigerator (A+ rated, 150W, 24hrs x 0.35 duty): 1,260Wh
• TV and entertainment: 300Wh
• Pumps and fans: 400Wh
• Mobile and laptop charging: 200Wh
• Total daily: 2,660Wh

Step 2: Battery Bank Ah

Bank Ah = (Daily Wh x Autonomy) / (System Voltage x DoD x 0.95)

Example: 48V system, 2,660Wh/day, 1-day autonomy, 80% DoD:

Bank Ah = (2660 x 1) / (48 x 0.80 x 0.95) = 69.3Ah

Use 4x CHISEN OPzV2-200 = 48V 200Ah (allows 3.2 days full backup)

Step 3: Solar Panel Oversizing

Design solar array to fully recharge the battery in 1 good day:

Panel Wp = (Daily Wh) / (Sun hours) x 1.3 (derating factor)

Example: 2,660Wh, 4 peak sun hours: (2660/4) x 1.3 = 865Wp minimum

Recommended: 1,200–1,500Wp panels for 48V 200Ah battery bank

Off-Grid vs Hybrid Sizing

• Off-grid: Size for 2–3 days autonomy. Higher battery cost, complete independence.
• Hybrid: Size for 1 day. Lower battery cost. Grid provides backup for extended cloudy periods.