Battery Bank Size Calculator
Determine the optimal battery bank capacity for your energy needs
Battery Bank Sizing
For Off-Grid and Backup Power Systems
Results:
Required Battery Bank Capacity (Ah): 0.00
How to Use the Calculator
Input Your Requirements
- Enter your daily Energy Demand in Watt-hours (Wh).
- Specify the number of Autonomy Days (how many days your system needs to run without charging).
- Input the Backup Hours per day your load will run.
Battery Parameters
- Set the desired Depth of Discharge (DoD) in percentage (e.g., 50% for lead-acid, 80-100% for lithium).
- Enter the nominal DC Voltage of your battery bank (e.g., 12V, 24V, 48V).
- Click "Calculate" to find the required Amp-hour (Ah) capacity.
Understanding DoD
- DoD is the percentage of battery capacity that has been discharged.
- Lower DoD extends battery lifespan.
- Always check your battery manufacturer's recommendations for optimal DoD.
Battery Sizing Fundamentals
Energy Demand
This is the total amount of energy your loads consume in a day, typically measured in Watt-hours (Wh). Accurate assessment is crucial for proper sizing.
Autonomy & Backup
Autonomy Days refer to how long your system can operate without any charging input (e.g., during cloudy days for solar). Backup Hours specify how long your load runs daily.
Depth of Discharge (DoD)
DoD is the percentage of the battery's capacity that has been used. For example, a 50% DoD means you've used half the battery's energy. Limiting DoD extends battery life.
DC Voltage
The nominal voltage of your battery bank (e.g., 12V, 24V, 48V). This affects the current draw and the number of batteries needed in series.
Key Formula:
Battery Capacity in Ah = (Energy Demand in Wh × Autonomy Days × Backup Hours) / (DoD in % × DC Voltage)
Calculation Formula
Battery Capacity in Ah:
Ah = (Wh × Days × Hours) / (DoD% × V)
Example Calculation
Let's calculate for a 900Wh daily load, 2 autonomy days, 3 backup hours, 50% DoD, and 12V DC system:
Energy Demand (Wh): 900 Wh
Autonomy Days: 2 Days
Backup Hours: 3 Hours
DoD: 50% (0.50)
DC Voltage: 12 Volts
Ah = (900 Wh × 2 Days × 3 Hours) / (0.50 × 12 Volts)
Ah = 5400 / 6 = 900 Ah
Required Battery Bank Capacity = 900 Ah
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