About the Solar Battery System Sizing Calculator
What is the Solar Battery System Sizing Calculator?
Off-grid and hybrid solar systems need batteries for nights and cloudy days. This solar battery sizing calculator works from your daily energy use and days of autonomy to the battery bank, the panels needed to recharge it and the charge controller.
Choose the system voltage – 24 V or 48 V suits most homes – and the battery type's usable depth of discharge.
How to use the Solar Battery System Sizing Calculator
- Daily Energy Use (Wh) (sample: 3,000)
- Days of Backup without Sun (sample: 1)
- System Voltage (sample: 24 V)
- Capacity of Each 12 V Battery (Ah) (sample: 150)
- Usable Depth of Discharge (%) (sample: 80)
- Inverter Efficiency (%) (sample: 90)
- Peak Sun Hours per Day (sample: 5)
- Panel Rating (Wp) (sample: 540)
- Press Size My Solar Battery System (results also refresh as you type). The result card shows the Battery Bank Needed, along with Batteries, Solar array needed, Panels and Charge controller rating.
Formula used
Battery bank (Ah) = Daily Wh × Days of autonomy ÷ (DoD × Inverter efficiency × System voltage)
- Solar array (Wp) = daily Wh ÷ (peak sun hours × 0.75)
- Charge controller (A) = array Wp ÷ system voltage × 1.25
Batteries in series add voltage; parallel strings add capacity.
Worked example
These are the sample values already filled in the calculator above, and the result it returns for them:
| Input | Sample value |
|---|---|
| Daily Energy Use (Wh) | 3,000 |
| Days of Backup without Sun | 1 |
| System Voltage | 24 V |
| Capacity of Each 12 V Battery (Ah) | 150 |
| Usable Depth of Discharge (%) | 80 |
| Inverter Efficiency (%) | 90 |
| Peak Sun Hours per Day | 5 |
| Panel Rating (Wp) | 540 |
| Result | Value |
|---|---|
| Battery Bank Needed | 174 Ah at 24 V |
| Batteries | 4 × 12 V 150 Ah (2 in series × 2 parallel) |
| Solar array needed | 800 Wp |
| Panels | 2 × 540 Wp |
| Charge controller rating | 56 A |
| Inverter size (for peak load) | Rate it for your highest simultaneous load plus 25% |
Tips for using the Solar Battery System Sizing Calculator
- Higher system voltages reduce current and cable size.
- MPPT charge controllers harvest 15–25% more energy than PWM controllers.