Battery Size Formula:
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Definition: This calculator determines the required battery bank size for solar power systems based on your energy needs and system parameters.
Purpose: It helps solar installers and DIY enthusiasts properly size battery banks for off-grid or backup power systems.
The calculator uses the formula:
Where:
Explanation: The formula calculates how much battery capacity you need to power your loads for the specified days while respecting the battery's recommended discharge depth.
Details: Correct battery sizing ensures reliable power availability, prolongs battery life by preventing excessive discharge, and helps optimize system costs.
Tips: Enter your daily energy consumption in Wh, desired days of autonomy (typically 1-3), depth of discharge (0.5 for lead-acid, 0.8 for lithium), and system voltage. All values must be > 0.
Q1: What's a typical DOD value?
A: For lead-acid batteries use 0.5 (50% discharge), for lithium batteries use 0.8 (80% discharge).
Q2: How do I find my daily load in Wh?
A: Multiply appliance wattage by hours used per day, then sum all appliances.
Q3: What's a good days of autonomy value?
A: 1-3 days is typical. More days provide more backup but increase cost.
Q4: Should I round up the battery size?
A: Yes, always round up to the nearest standard battery size available.
Q5: Does this include efficiency losses?
A: No, consider multiplying the result by 1.1-1.2 to account for system inefficiencies.