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Battery Capacity Formula:
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The Inverter Battery Size Calculator helps determine the appropriate battery capacity (in ampere-hours) needed for a solar power system based on your inverter's output power, desired autonomy time, and system voltage.
The calculator uses the following formula:
Where:
Explanation: The formula calculates the total energy needed (watt-hours) and converts it to battery capacity (ampere-hours) based on your system voltage.
Details: Correct battery sizing ensures your solar system can meet power demands during periods without sunlight, prevents battery damage from over-discharge, and optimizes system cost and performance.
Tips: Enter your inverter's continuous output rating in watts, desired backup time in hours, and system voltage in volts. All values must be positive numbers.
Q1: Should I add a safety margin to the calculated battery size?
A: Yes, it's recommended to add 20-30% to account for battery aging, efficiency losses, and unexpected load increases.
Q2: What's the typical autonomy time for solar systems?
A: Most residential systems use 1-3 days autonomy. Off-grid systems may need 3-5 days, while grid-tied systems with backup may only need 0.5-1 day.
Q3: How does battery type affect the calculation?
A: Lead-acid batteries should only be discharged to 50% capacity, while lithium batteries can often discharge to 80-90%. Adjust your total capacity accordingly.
Q4: What if my system has multiple batteries?
A: This calculator gives total capacity needed. Divide by individual battery capacity to determine how many batteries you need in parallel.
Q5: Does temperature affect battery sizing?
A: Yes, cold temperatures reduce battery capacity. In cold climates, you may need to increase battery size by 10-20%.