Sizing Battery For Solar System

Battery Capacity Formula:

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

System Daily Energy:

Days of Autonomy:

days

Battery Voltage:

Depth of Discharge:

(0-1)

Battery Efficiency:

(0-1)

Battery Capacity:

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is Battery Capacity Calculation?

The battery capacity calculation determines the required battery bank size (in amp-hours) for a solar power system based on energy needs, autonomy days, and system characteristics. Proper sizing ensures reliable power supply during periods without sunlight.

2. How Does the Calculator Work?

The calculator uses the following equation:

Where:

System Daily Energy — Total watt-hours consumed per day
Days of Autonomy — Number of days system should run without sun
Battery Voltage — System voltage (typically 12V, 24V, or 48V)
Depth of Discharge — Fraction of battery capacity that can be used (typically 0.5-0.8)
Battery Efficiency — Charge/discharge efficiency (typically 0.8-0.95)

Explanation: The equation accounts for total energy needed, battery system characteristics, and safety factors to prevent over-discharge.

3. Importance of Proper Battery Sizing

Details: Correct battery sizing prevents system failures, extends battery life, and ensures reliable power availability. Oversizing increases costs while undersizing reduces system reliability.

4. Using the Calculator

Tips: Enter daily energy consumption in watt-hours, desired autonomy days, battery bank voltage, depth of discharge (typically 0.5 for lead-acid, 0.8 for lithium), and round-trip efficiency (typically 0.85).

5. Frequently Asked Questions (FAQ)

Q1: What's a typical depth of discharge?
A: Lead-acid batteries: 50% (0.5), Lithium batteries: 80% (0.8). Deeper discharges reduce battery lifespan.

Q2: How many days of autonomy should I use?
A: Typically 2-5 days depending on location (sunny vs cloudy areas) and criticality of the load.

Q3: What's battery efficiency?
A: Typically 85% (0.85) for lead-acid, 95% (0.95) for lithium. This accounts for energy lost during charge/discharge cycles.

Q4: Should I add a safety factor?
A: Yes, consider multiplying result by 1.2-1.5 to account for battery aging and unexpected loads.

Q5: How does temperature affect capacity?
A: Battery capacity decreases in cold temperatures. For temperatures below 20°C (68°F), additional capacity may be needed.