1. What is a Solar System Battery Calculator?

Definition: This calculator estimates the battery capacity needed for a solar power system based on daily energy consumption, desired autonomy days, system efficiency, and battery depth of discharge.

Purpose: It helps solar system designers and homeowners determine the appropriate battery bank size for off-grid or backup power systems.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• Battery — Required battery capacity (watt-hours)
• Daily Use — Daily energy consumption (watt-hours)
• Autonomy — Days of backup power needed
• Efficiency — System efficiency factor (0-1)
• DOD — Battery depth of discharge (0-1)

Explanation: The daily energy multiplied by autonomy days gives total needed energy, which is then adjusted for system losses and battery discharge limits.

3. Importance of Battery Sizing

Details: Proper battery sizing ensures reliable power availability, maximizes battery life, and prevents over-dimensioning which increases costs.

4. Using the Calculator

Tips: Enter your daily energy use in watt-hours, desired days of autonomy (default 3), system efficiency (default 0.85), and depth of discharge (default 0.5). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is Depth of Discharge (DOD)?
A: DOD is the percentage of battery capacity that can be safely used (e.g., 0.5 means only 50% of battery capacity should be used).

Q2: Why is system efficiency important?
A: Efficiency accounts for losses in inverters, wiring, and other components (typically 80-90% for most systems).

Q3: How do I determine my daily energy use?
A: Sum the watt-hours of all devices you'll power, multiplied by their daily usage hours.

Q4: What's a typical autonomy period?
A: For off-grid systems, 3-5 days is common to account for cloudy periods.

Q5: Should I add a safety margin?
A: Yes, consider adding 10-20% to the calculated capacity for aging and unexpected loads.