Calculator

Solar Battery Sizing Calculator

Battery adds a lot of cost and usually does not pay for itself. Buy it if you need backup during power cuts, not because you think it saves money. This shows both sides.

Backup requirement

Fans, lights, fridge, router — not the AC
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The formula

Battery Ah = (Load in watts x Backup hours) / (System voltage x DoD x Inverter efficiency) DoD = how much of the battery you can actually use Lead acid 0.50 Tubular 0.60 Lithium 0.80 to 0.90 Inverter efficiency 0.85 to 0.90 COST PER CYCLE Battery price / (Cycle life x DoD x Capacity in kWh) Lithium looks costlier but usually works out cheaper per cycle.

What this assumes

  • Assumes normal daily use. Deep discharge every day shortens battery life a lot.
  • Lead acid batteries need water topping up and proper ventilation.
  • Battery life depends heavily on temperature. Indian summers are hard on batteries.
  • Cycle life figures come from manufacturers and are usually best case.
  • A battery does not increase your solar savings. It only gives you backup.

Common questions

Do I need a battery with solar?

Honestly, most people do not. If your area has decent power supply, skip it. A battery roughly doubles your system cost and gives you backup, not savings. If you have long daily power cuts, then yes, it makes sense.

Lead acid or lithium?

Lithium costs about twice as much upfront but lasts three to four times longer, needs no maintenance and you can use more of its capacity. Work out cost per cycle, not sticker price. Lithium usually wins.

What size battery for my home?

Depends on what you want to run and for how long. Fans and lights for 4 hours needs far less than running an AC. Enter your actual load in the calculator.

Will a battery reduce my electricity bill?

Barely. Solar reduces your bill. The battery just stores it for when the grid is down. If your goal is a lower bill, spend the money on more panels instead.

Data last reviewed August 2026 Full methodology Disclaimer