Solar Battery Storage Size Calculator
By Santaji GadepatilinUpdated October 27, 2026
A home battery stores solar energy for use at night or during power cuts. Its size depends on how much energy you use and how deeply the battery can be discharged. This free solar battery storage size calculator solves for whichever value you leave blank and shows the formula and steps.
How to use the solar battery storage size calculator
Enter the daily energy you want covered, days of autonomy, usable depth of discharge, round-trip efficiency and the battery bank voltage. Capacity in kWh and Ah is calculated.
Example
6 kWh a day, 1 day of backup, 90% DoD, 90% efficiency, 48 V bank:
- Capacity = 6 ÷ 0.81 = 7.4 kWh
- = 154 Ah at 48 V
Battery chemistries compared
| Chemistry | Usable depth of discharge | Cycle life (approx.) | Round-trip efficiency |
|---|---|---|---|
| Lead-acid (flooded) | 50% | 500–1,500 | 75–85% |
| AGM / gel lead-acid | 50–60% | 500–1,500 | 80–85% |
| Lithium iron phosphate (LFP) | 80–100% | 3,000–6,000+ | 90–95% |
| Lithium NMC | 80–90% | 1,000–3,000 | 90–95% |
LFP is now the most common choice for home solar storage because of its long life and safety.
Capacity by daily load
1 day of autonomy, 80% DoD, 90% efficiency:
| Daily load | Battery needed | At 48 V |
|---|---|---|
| 2 kWh | 2.8 kWh | 58 Ah |
| 4 kWh | 5.6 kWh | 116 Ah |
| 6 kWh | 8.3 kWh | 174 Ah |
| 10 kWh | 13.9 kWh | 289 Ah |
| 15 kWh | 20.8 kWh | 434 Ah |
| 20 kWh | 27.8 kWh | 579 Ah |
Essential loads only
For backup during outages, many homes size the battery for essential loads only: lights, fridge, internet, fans and a few sockets. This can cut the battery size by half or more.
Inverter size
The inverter must handle the highest power drawn at once, not the daily energy. A home with a 3 kW peak load needs at least a 3–4 kW inverter, with extra surge capacity for motor starts.
Battery life in years
Cycle life ÷ cycles per year gives a rough lifetime. An LFP battery rated for 6,000 cycles, used once a day, could last over 15 years, though calendar ageing also reduces capacity.
Frequently asked questions
How big a battery do I need?
Daily load × days of backup, divided by usable depth of discharge and efficiency.
What depth of discharge should I use?
About 80–95% for lithium iron phosphate (LFP) batteries and about 50% for lead-acid to protect battery life.
How do I convert kWh to Ah?
Ah = kWh × 1,000 ÷ battery voltage.
How many kWh battery do I need for my home?
Divide your daily energy need by DoD × efficiency. For 6 kWh a day with LFP (80% DoD, 90% efficiency), about 8.3 kWh.
How do I convert kWh to Ah?
Ah = kWh × 1,000 ÷ battery voltage. 10 kWh at 48 V is about 208 Ah.