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Updated July 2026

Solar Battery & Backup Calculators

Plan power-cut protection properly: size the battery bank for your backup loads, match the inverter rating and know how fast your panels can recharge it all.

Solar Battery Calculator Battery size in kWh and Ah for your backup load, lithium vs lead-acid compared. Solar Inverter Size Calculator The right inverter VA/kVA for your load and the right kW for your panels. Battery Charging Time Calculator How long a solar panel takes to charge any battery, with real derating.

Designing Backup That Actually Works

Backup fails for predictable reasons: the battery is sized to a price point instead of the load, the inverter cannot start the fridge compressor, or the panels cannot refill the bank between evening outages. The three calculators here attack exactly those failure points, in order:

  1. Battery: decide what must run in a cut and for how long; the solar battery calculator converts that into kWh and Ah for lithium or lead-acid.
  2. Inverter: the inverter size calculator checks the VA rating carries your simultaneous load with motor-start headroom.
  3. Recharge: the charging time calculator confirms your panel watts can refill the bank in a day.

Going fully off the grid? Work through the complete off grid solar system calculation guide.

The Backup Budget Rule of Thumb

Before detailed sizing, sanity-check the budget with one rule: essentials backup costs roughly ₹18,000 to ₹22,000 per hour of autonomy in lithium (an ~800W household list), while adding one 1.5 ton AC multiplies that by about three. So a 4-hour essentials setup lands near ₹80,000 in storage, and the same 4 hours with an AC nears ₹2.4 lakh before the inverter upgrade. If the quick number fits your budget, proceed to the battery calculator for the precise bank; if it does not, shorten the hours or trim the list before falling in love with a spec sheet.

Solar Battery Calculators: Frequently Asked Questions

What battery size do I need for home backup?+
Essentials (fans, lights, fridge, TV, Wi-Fi, about 800W) for 4 hours need roughly 4.4 kWh of lithium or 7.5 kWh of lead-acid. Add ACs and the numbers triple, which is why loads are chosen before chemistry.
Do I need all three calculators?+
For a hybrid or off-grid build, yes, in order: battery, then inverter, then charging check. For an on-grid system without storage you need none of them; on-grid inverter sizing is covered on the inverter page too.
Lithium or lead-acid for home solar backup?+
Lithium for daily cycling: longer life, more usable capacity and faster charging make it cheaper per delivered kWh. Lead-acid still suits rare-outage areas where upfront cost matters most.
Does a battery increase my solar savings?+
No, it adds cost and small losses; its job is reliability. If your grid is stable, an on-grid system saves more. Check both scenarios in the savings and payback calculator.
What does battery backup cost per hour of autonomy?+
For an essentials load around 800W, budget ₹18,000 to ₹22,000 of lithium per backed-up hour, or about half that in lead-acid upfront (with a shorter life). Adding an AC roughly triples the per-hour figure, which is why backup lists matter more than brands.

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