Solar Battery Bank Sizing

Battery Bank Capacity Formula:

\[ \text{Battery Bank Capacity (Ah)} = \frac{\text{Solar Daily Energy (Wh)} \times \text{Autonomy Days}}{\text{Voltage (V)} \times \text{Depth of Discharge}} \]

Solar Daily Energy:

Autonomy Days:

days

System Voltage:

Depth of Discharge:

decimal (0-1)

Battery Bank Capacity:

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is Solar Battery Bank Sizing?

Solar battery bank sizing determines the capacity needed for your battery storage system to meet your energy requirements during periods without sunlight, accounting for your daily energy usage, desired autonomy days, system voltage, and battery depth of discharge.

2. How Does the Calculator Work?

The calculator uses the following equation:

\[ \text{Battery Bank Capacity (Ah)} = \frac{\text{Solar Daily Energy (Wh)} \times \text{Autonomy Days}}{\text{Voltage (V)} \times \text{Depth of Discharge}} \]

Where:

Solar Daily Energy — Your daily energy consumption in watt-hours
Autonomy Days — Number of days you want the system to run without sun
Voltage — Your battery bank system voltage (typically 12V, 24V, or 48V)
Depth of Discharge — Fraction of battery capacity that can be used (typically 0.5 for lead-acid, 0.8 for lithium)

Explanation: The equation calculates the required battery capacity in amp-hours (Ah) to meet your energy needs for the specified autonomy period while respecting the battery's recommended depth of discharge.

3. Importance of Proper Battery Sizing

Details: Correct battery sizing ensures your solar system can meet your energy needs during cloudy periods while maximizing battery life by not over-discharging. Undersized batteries may not provide enough power, while oversized systems are unnecessarily expensive.

4. Using the Calculator

Tips:

Calculate your daily energy needs accurately by summing all loads
Typical autonomy days range from 2-5 depending on location and reliability needs
Use manufacturer-recommended depth of discharge values
For lead-acid batteries, common DoD is 50% (0.5)
For lithium batteries, common DoD is 80% (0.8)

5. Frequently Asked Questions (FAQ)

Q1: What's a typical depth of discharge for different battery types?
A: Lead-acid: 50% (0.5), Lithium-ion: 80% (0.8), Saltwater: 100% (1.0)

Q2: How do I calculate my daily energy needs?
A: Sum the watt-hours of all devices you'll power (Watts × Hours used per day)

Q3: What are typical autonomy days?
A: 2-3 days for most residential systems, up to 5 for critical loads or areas with frequent clouds

Q4: Should I round up the battery capacity?
A: Yes, always round up to the nearest standard battery size to ensure sufficient capacity

Q5: Does temperature affect battery capacity?
A: Yes, cold temperatures reduce capacity. Add 10-20% capacity in cold climates.