Solar Battery Backup Calculator (2026)

Enter your AC, extra load and the backup hours you want, and get the battery bank size in kWh and Ah — with LiFePO4 and lead-acid options costed side by side for Indian homes.

Overnight power-cut sizing LiFePO4 vs lead-acid Free · no sign-up
Tonnage
Star rating
We use the AC's average overnight draw — an inverter AC holding a set temperature uses far less than its nameplate watts.
Fans, lights, Wi-Fi, fridge
200 W
A typical bedroom set is 150–300 W.
Hours of power cut to cover
8 h
Summer power cuts in much of India cluster overnight — 8 hours covers 10 PM to 6 AM.
Advanced
Ah figures below are quoted at this bank voltage. AC-capable inverters are usually 24 V or 48 V.

How does it work?

  1. You enter the AC you want to run, any other load, and how many hours of backup you need.
  2. The AC's running draw = cooling capacity ÷ its ISEER — holding a set temperature overnight draws well under its nameplate watts.
  3. Energy needed = (AC draw + other load) × backup hours ÷ 90% inverter efficiency.
  4. Bank size = that energy ÷ the chemistry's usable depth of discharge: ~80% for LiFePO4, ~50% for flooded lead-acid.
  5. That is why the same backup needs a much bigger, heavier lead-acid bank — and why LiFePO4 usually costs less per cycle despite the sticker premium.

Prices are 2026 India market ballparks for the battery alone, excluding the inverter or PCU.

More solar tools on TheDiscomBill

Solar Panel Size Calculator — panels, roof area and cost to run these loads in the daytime.  ·  Rooftop Solar Savings Calculator — PM Surya Ghar subsidy, monthly savings and payback.  ·  Electricity Cost Calculator — work out your full monthly consumption.

Before you size a battery

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