Correctly sizing a solar battery bank prevents premature battery failure and ensures your system meets daily energy needs. This step-by-step guide covers the complete formula with worked examples for residential, commercial, and off-grid systems.
The Solar Battery Sizing Formula
Battery Bank (Ah) = Daily Wh / (System Voltage x DoD x Inverter Efficiency)
KEY STATISTICS
Step 1: Calculate Daily Energy Consumption
- LED lighting: 10 x 10W x 5 hrs = 500Wh
- Refrigerator: 150W x 24hrs x 0.4 duty cycle = 1,440Wh
- TV: 50W x 4 hrs = 200Wh
- Laptop: 30W x 5 hrs = 150Wh
- Total daily consumption: 2,290Wh/day
Step 2: Choose System Voltage
| System Size | Voltage | When to Use |
|---|---|---|
| < 3kWh/day | 12V | Small cabins, weekend use, minimal loads |
| 3–10kWh/day | 24V | Standard residential solar |
| > 10kWh/day | 48V | Commercial, industrial, large off-grid |
Sizing Examples
| Application | Daily Wh | Voltage | DoD | Days | Required Ah | CHISEN OPzV Config |
|---|---|---|---|---|---|---|
| Small cabin | 2,000Wh | 48V | 80% | 2 | 104Ah | 4x OPzV2-200 (200Ah) |
| Residential | 5,000Wh | 48V | 80% | 1 | 130Ah | 4x OPzV2-300 (300Ah) |
| Small biz | 10,000Wh | 48V | 80% | 2 | 547Ah | 4x OPzV2-300 x 4 strings |
| Large off-grid | 20,000Wh | 48V | 80% | 3 | 1,563Ah | 24x OPzV2-1000 |
Frequently Asked Questions
How many solar panels do I need to recharge a battery bank?
Solar panels should be sized at 1.2–1.3x daily battery discharge to achieve full recharge. Example: 5,000Wh daily use needs 6,000–6,500Wh of solar output. In practice, location, orientation, and temperature reduce output by 15–25%.
What happens if the battery bank is undersized?
An undersized bank discharged beyond design DoD daily dramatically reduces cycle life. A battery rated for 1,200 cycles at 50% DoD may deliver only 200–300 cycles if regularly discharged to 90%.
Can I add batteries to an existing bank later?
Yes, but only if new batteries are the same age, type, capacity, and manufacturer. Mixing old and new batteries causes imbalance that shortens all battery life.
Need a Reliable Battery Supplier?
CHISEN Battery — 8 global factories, 70M kVAh/year. OPzV tubular GEL, AGM VRLA, front terminal batteries. Trusted by distributors in 60+ countries.
| Factory | 8 global factories |
| Capacity | 70 million kVAh/year |
| Certifications | CE, ISO9001, ISO14001, TUV Rheinland |
| Tel | +86 131 2666 8999 |
| jack@chisen.cn | |
| Web | www.chisen.cn |