New
Solar Panel Calculator
Panel count, wattage & cost for your home or business. BD & global.
CostNest Calculator
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, AGM and flooded lead-acid. No account needed — numbers update as you type.
Step By Step
How to Use the Solar Battery Backup Calculator
7 steps
- Select battery chemistry (LiFePO4 recommended for BD).
- Enter your daily energy use in kWh.
- Set how many hours of backup you need.
- Set autonomy days (cloudy/no-sun days).
- Choose system voltage (48V recommended).
- Enter currency and battery price per kWh.
- Review battery count, Ah, bank size and total cost.
Worked Example
Worked Example for Solar Battery Backup Calculator
Use this sample to sanity-check your inputs and understand what the final result represents.
- 1Daily usage: 5 kWh · Backup needed: 8 hrs
- 2Energy for backup: 5 ÷ 24 × 8 = 1.67 kWh
- 3LiFePO4 DoD 90%, efficiency 97%
- 4Required capacity: 1.67 ÷ (0.90 × 0.97) = 1.91 kWh
- 548V system: 1,910 ÷ 48 = ~40 Ah needed
Final Result
Result: 1 × 100Ah LiFePO4 battery · 4.8 kWh bank · ~৳96,000
Methodology
Solar Battery Backup Calculator Formula & Methodology
This section explains the calculation logic, assumptions, and source material used to make the result more trustworthy and easier to verify.
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.