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Solar Battery Backup Calculator
Calculate the right battery bank size (kWh and Ah), number of batteries, configuration, and total cost for your solar system. Supports LiFePO4, Li-Ion, AGM and flooded lead-acid. Works for off-grid and hybrid setups in Bangladesh and globally.
Solar Battery Backup Calculator
Battery size (kWh · Ah) · Bank cost · Backup hours · Autonomy days
Average BD home: 3–8 kWh/day
Days of backup without solar charge
Default: ৳20,000/kWh (LiFePO4)
48V systems are most efficient for home solar in Bangladesh. LiFePO4 is the recommended chemistry — safer in BD heat, no maintenance, and lasts 10+ years. Lead-acid is cheaper but degrades faster in tropical heat.
How to Use
- 1Select battery chemistry (LiFePO4 recommended for BD).
- 2Enter your daily energy use in kWh.
- 3Set how many hours of backup you need.
- 4Set autonomy days (cloudy/no-sun days).
- 5Choose system voltage (48V recommended).
- 6Enter currency and battery price per kWh.
- 7Review battery count, Ah, bank size and total cost.
Example Calculation
- Daily usage: 5 kWh · Backup needed: 8 hrs
- Energy for backup: 5 ÷ 24 × 8 = 1.67 kWh
- LiFePO4 DoD 90%, efficiency 97%
- Required capacity: 1.67 ÷ (0.90 × 0.97) = 1.91 kWh
- 48V system: 1,910 ÷ 48 = ~40 Ah needed
Result: 1 × 100Ah LiFePO4 battery · 4.8 kWh bank · ~৳96,000
Formula Used
Energy for backup = (Daily kWh ÷ 24) × backup hours × autonomy days. Required capacity (kWh) = Energy ÷ (DoD × efficiency). Required Ah = Capacity × 1000 ÷ system voltage. Batteries in parallel = ceil(Required Ah ÷ battery Ah). Batteries in series = system voltage ÷ 12V. Total batteries = series × parallel.
Frequently Asked Questions
What battery size do I need for a 3 kWp solar system in Bangladesh?
For a 3 kWp hybrid system with 8 hours of backup and 5 kWh daily usage, you typically need a 10–15 kWh battery bank. Using LiFePO4 at 90% DoD and 48V, that means approximately 4 × 200Ah LiFePO4 batteries. This calculator gives exact numbers based on your actual load and backup hours.
LiFePO4 vs Lead-Acid — which is better for Bangladesh?
LiFePO4 (Lithium Iron Phosphate) is strongly recommended for Bangladesh. It handles high temperatures better than lead-acid, lasts 4,000+ cycles (10+ years), requires zero maintenance, and is much lighter. Lead-acid (AGM or flooded) is cheaper upfront but degrades faster in BD heat and needs regular maintenance. LiFePO4 total cost of ownership over 10 years is usually lower.
What is Depth of Discharge (DoD)?
DoD is the percentage of battery capacity you can safely use. LiFePO4 allows 90% DoD, meaning a 10 kWh battery gives 9 kWh usable energy. Lead-acid should only be discharged to 50% to avoid permanent damage. This calculator accounts for DoD automatically.
What voltage system should I use — 12V, 24V, or 48V?
48V is the most efficient for home solar systems in Bangladesh and is highly recommended. It reduces current (and therefore cable losses and heat) by 4× compared to 12V. Most modern inverters for 2–10 kW systems use 48V. Small portable systems under 500W can use 12V or 24V.
What is the price of LiFePO4 batteries in Bangladesh?
LiFePO4 batteries in Bangladesh (2025-26): approximately ৳15,000–25,000 per kWh depending on brand, capacity, and seller. A 10 kWh LiFePO4 bank costs ৳150,000–250,000. Chinese brands (CATL-cell based) are cheaper; branded systems (Pylontech, REPT, EVE) cost more but have better warranty.