Free · Battery · Inverter · Backup
Solar Battery
& Inverter Calculator
Size your battery bank, inverter and recharge panels for backup power — in seconds.
Backup hours
LFP vs lead-acid
Solar recharge
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Your backup needs
Fridge + lights + internet ≈ 1–2 kW
Solar recharge (optional)
Recommended system
Usable energy needed
17.8 kWh
after inverter losses & depth of discharge
Batteries needed
2 × 5 kWh
Inverter size
3 kW
Panels to recharge / day
16 panels
Backup duration with 2 × 5 kWh
8.1 h
Calculations: energy = load × hours ÷ inverter efficiency (90%); capacity = energy ÷ DoD; batteries = ceil(capacity ÷ battery size); inverter = max(load × 1.25, 3 kW minimum); panels = energy ÷ (sun × panelW × 0.8).
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LFP is the new standard
Lithium iron phosphate batteries allow 90%+ depth of discharge and 5,000+ cycles. Lead-acid is cheaper upfront but only ~50% usable.
Backup ≠ whole house
Most homes run essential loads on battery — fridge, lights, internet. Whole-house backup needs 15+ kWh and a large inverter.
Pair with solar
A battery lets you store daytime solar for the evening and keeps you powered through outages. Size the solar array to recharge it in one good sun day.
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FAQ
Battery calculator FAQ
How big a battery do I need for backup power?
Multiply your backup load (kW) by the hours you want to cover, divide by the inverter efficiency, then divide by the usable depth of discharge. A 2 kW load for 8 hours needs about 2×8/0.9/0.9 ≈ 20 kWh usable — 2× LFP batteries.
What is depth of discharge (DoD)?
The usable percentage of a battery's capacity. LFP batteries allow ~90–100% DoD; lead-acid only ~50%. Using more than the DoD shortens battery life.
How many solar panels to recharge a battery in a day?
Divide the daily energy used by (peak sun hours × panel power × system efficiency). For 20 kWh/day at 4 sun hours and 400 W panels at 80% efficiency: 20/(4×0.4×0.8) ≈ 16 panels.
How big should my inverter be?
Your inverter must handle the peak backup load plus a safety margin (usually ×1.25), and at least match your solar array's output. A 5 kW inverter covers most homes.
LFP or lead-acid for solar storage?
LFP (lithium) is the modern choice: higher DoD, longer life (5,000+ cycles) and no maintenance. Lead-acid is cheaper upfront but only ~50% DoD and shorter-lived.
How long does a solar battery last?
Quality LFP batteries are rated for 5,000–6,000 cycles — roughly 10–15 years of daily cycling. Many carry a 10-year warranty.
Can a battery power my whole house?
Only with a large battery and inverter (10+ kWh and a big inverter). Most homes use a battery for essential loads — lights, fridge, internet — during an outage.
Should I oversize the battery for future EV charging?
If you plan to charge an EV at home, add ~10 kWh per day of EV use. It is usually cheaper to buy enough battery once than to expand later.
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