Solar Battery Size Calculator 2026

Recommended battery bank

Total Ah @ System V

122 Ah

@ 48V bank

Battery Count

1 series × 2 parallel

Usable Capacity

8.64 kWh

Nominal 9.6 kWh

Estimated Cost

₹1,03,680

up to ₹1,55,520

Wiring summary

Required Energy

5 kWh

Per-battery Usable Ah

90 Ah

Series per string

Parallel strings

Prices are indicative for 2026 India market. Installation, charge controller, and cabling are extra.

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How to size a solar battery bank

Step-by-step guide to calculating battery Ah and bank configuration from load and backup requirements.

Calculate daily energy to backup

Use our appliance load calculator or pick essentials: fan (75W × 10h), fridge (150W × 24h), lights, router. Total kWh per day = energy to store.

Pick days of autonomy

1 day for grid-backup, 2-3 for off-grid cloudy reserve.

Choose system voltage

12V for small loads under 500W, 24V for 500-2000W, 48V for 2000W+. Higher voltage = thinner cables, better MPPT efficiency.

Choose battery chemistry

LiFePO₄ for longevity, tubular for daily cycling on a budget, lead-acid only for occasional backup.

Review wiring plan

Our calculator outputs series + parallel configuration. Avoid mixing old + new batteries in the same string.

Add a BMS and fusing

Every parallel string should have its own fuse. Lithium banks need a BMS for cell balancing.

The right way to size a solar battery bank

Battery sizing is the step where most home solar projects either lock in real cost savings or silently over-spend for years. The math is not hard — but the gotchas around depth of discharge (DoD), round-trip efficiency, battery chemistry, and parallel-string imbalance are where buyers get hurt. This calculator gives you a conservative, production-ready sizing plan in seconds.

The core equation is: Total Ah = (Daily kWh × days of autonomy × 1000) ÷ (System voltage × DoD × round-trip efficiency). For a 5 kWh daily load, 1 day autonomy, 48V lithium bank (DoD 0.9, η 0.95): 5000 ÷ (48 × 0.9 × 0.95) ≈ 122 Ah. On a 100 Ah per battery preset, that rounds up to 2 × 100Ah lithium batteries in a 48V 200Ah bank. Straightforward — until you add lead-acid or tubular, where DoD drops to 50-60% and your bank doubles in size for the same usable energy.

Chemistry cheat-sheet (2026 prices)

Chemistry	DoD	Cycles	₹ / Usable Wh	Best For
LiFePO₄ (Lithium)	90%	3,000-6,000	₹12-18	Long-life, daily cycling
Tubular	60%	1,500-2,000	₹7-10	Budget UPS cycling
Lead-Acid (Flooded)	50%	500-800	₹6-9	Occasional backup only

Once you've picked the bank, verify the rest of the off-grid chain: the inverter size matches the bank voltage, the backup hours align with your real load, and the DC cable size handles the full discharge current without voltage drop.

Series-parallel wiring basics

Batteries connect in series to multiply voltage (4 × 12V batteries = 48V bank) and in parallel to multiply capacity (2 strings of 100 Ah = 200 Ah bank). Our calculator shows the exact combination. A few rules:

Use identical batteries — same model, same age, same manufacture date.
Each parallel string gets its own fuse and balanced-length busbar runs.
Don't exceed 3-4 parallel strings without a monitor; imbalance shortens the bank's life.
Add a battery management system (BMS) for lithium — cell balancing and over-discharge protection are critical.
Keep batteries in a ventilated, temperature-controlled area (20-30°C is ideal).

Frequently Asked Questions

How do I calculate the battery size for solar?

Multiply your daily backup kWh by days of autonomy, then divide by (system voltage × depth of discharge × efficiency). For a 5 kWh daily load on a 48V lithium bank: 5000 Wh ÷ (48V × 0.9 × 0.95) ≈ 122 Ah. Our calculator rounds to the nearest commercial battery size and plans series/parallel wiring.

What is depth of discharge (DoD) and why does it matter?

DoD is the usable fraction of the battery's nominal capacity. Lithium = 90%, lead-acid = 50%, tubular = 60%. A 200 Ah lead-acid battery only gives you 100 Ah of real work; a 200 Ah LiFePO₄ gives you 180 Ah. That's why lithium is cheaper per usable kWh even though the sticker price is higher.

Lead-acid vs tubular vs lithium — which should I pick in 2026?

Lithium (LiFePO₄) has become the default for new systems — 8-10 year life, 90% DoD, no maintenance, ₹12-18/Wh usable. Tubular is still popular for UPS-style daily cycling (₹7-10/Wh usable). Lead-acid only makes sense for occasional backup (≤₹9/Wh but dies in 3 years).

How many batteries do I need in series vs parallel?

Series adds voltage (4 × 12V = 48V bank), parallel adds capacity (2 strings of 100 Ah = 200 Ah bank). Your calculator needs to hit both your system voltage and total Ah. Avoid more than 3-4 parallel strings — imbalance shortens lifespan.

Does days-of-autonomy really matter if I have solar panels?

For grid-tied systems with net metering, 1 day is enough (overnight backup). For pure off-grid, plan 2-3 days to cover cloudy weather. Fully autonomous systems (remote sites, no backup power) need 3-5 days. More autonomy = bigger bank = more money.

Do I need a battery management system (BMS) for lithium?

Yes — every lithium bank needs an integrated BMS that handles cell balancing, over-temperature, and over-discharge protection. Most modern LiFePO₄ batteries come with a built-in BMS, but verify with the seller before buying. Running lithium without a BMS is dangerous.

What is the cost of a 5 kWh battery bank in 2026?

5 kWh usable = 5000 Wh. At ₹14/Wh (lithium mid-range) = ~₹70,000. Lead-acid equivalent (needing 10 kWh nominal for 5 kWh usable) = ~₹60,000. Lithium wins over 2-3 cycles per day thanks to longer life.

How long will my battery bank last?

Lithium LiFePO₄: 3,000-6,000 cycles (8-10 years at 1 cycle/day). Tubular: 1,500-2,000 cycles (5-7 years). Lead-acid: 500-800 cycles (2-3 years). Depth of discharge, ambient temperature, and charging quality all affect real-world life.

Solar Battery Size Calculator

Step 1 — Backup requirements

Step 2 — Battery chemistry & size