Solar Panel Battery Calculator
Size a battery bank for your solar panel system. Compare lithium vs lead-acid batteries by capacity, cost, weight, and lifespan.
Lithium vs Lead-Acid Comparison
| Specification | Lithium (LiFePO4) | Lead-Acid (AGM) |
|---|---|---|
| Depth of Discharge | 80% | 50% |
| Usable Capacity Needed | 75 kWh | 120 kWh |
| Battery Bank (Ah) | 1,562 Ah @ 48V | 2,500 Ah @ 48V |
| Estimated Cost | $11,250 | $12,000 |
| Estimated Weight | 975 lbs | 6,600 lbs |
| Expected Lifespan | 10 years | 5 years |
| 10-Year Total Cost | $11,250 | $24,000 |
How It Works
This calculator determines the total battery bank capacity needed for your solar system based on your daily energy consumption, desired days of backup autonomy, and battery chemistry.
Battery Bank (kWh) = Daily Usage (kWh) x Days of Autonomy / Depth of Discharge. The Ah rating is then derived by dividing total watt-hours by the system voltage.
The comparison table shows side-by-side specs for lithium (LiFePO4) and lead-acid (AGM) batteries, including the 10-year total cost of ownership factoring in replacement cycles.
Frequently Asked Questions
How do I calculate the battery bank size for my solar system?
Multiply your daily energy usage (kWh) by the number of days of autonomy you want, then divide by the battery depth of discharge (DoD). For example, 30 kWh/day with 2 days of autonomy and 80% DoD lithium batteries requires 75 kWh of total battery capacity.
What is depth of discharge (DoD) and why does it matter?
Depth of discharge is the percentage of a battery's total capacity that can be safely used without damaging it. Lithium batteries can safely discharge to 80–90%, while lead-acid batteries should only be discharged to 50%. This means lead-acid batteries need roughly twice the total capacity to deliver the same usable energy.
Is lithium or lead-acid better for solar battery storage?
Lithium (LiFePO4) batteries are better for most solar installations. They have higher DoD (80% vs 50%), last 10+ years vs 5 years for lead-acid, weigh 75% less, and have a lower 10-year total cost despite higher upfront price. Lead-acid may still be suitable for budget-conscious projects or infrequent use.
Should I choose 12V, 24V, or 48V for my battery bank?
48V systems are recommended for most home solar installations. Higher voltage means lower current for the same power, which allows smaller wire sizes and reduces energy losses. 12V systems are suitable only for small setups like RVs or sheds. 24V works for medium off-grid cabins.