Pure sine wave inverters are the safe choice for fridges, pumps, electronics and anything with a motor or a sensitive power supply.
How the battery bank calculator works
BatteryBankCalc adds watts × hours × quantity for every load to get watt-hours per day. Battery watt-hours = daily Wh × days of autonomy ÷ (usable depth of discharge × inverter efficiency), and amp-hours = that ÷ system voltage. Batteries in series = system voltage ÷ battery voltage; strings in parallel = amp-hours needed ÷ battery amp-hours, rounded up. Inverter = sum of all load watts × (1 + headroom), rounded up to a standard size. Solar array = daily Wh ÷ inverter efficiency ÷ (peak sun hours × system efficiency); controller amps = installed panel watts ÷ system voltage × 1.25.
Usable capacity by battery type
| Battery | Typical usable depth of discharge | Usable Wh from 12 V 100 Ah |
|---|---|---|
| Lithium iron phosphate (LiFePO4) | 80% | 960 Wh |
| AGM / gel lead-acid | 50% | 600 Wh |
| Flooded lead-acid | 50% | 600 Wh |
Batteries in series for each system voltage
| System | 12 V batteries in series | Current for a 1,000 W load |
|---|---|---|
| 12 V | 1 | 83.3 A |
| 24 V | 2 | 41.7 A |
| 48 V | 4 | 20.8 A |
Depth of discharge, inverter efficiency (90%), solar system efficiency (80%) and the 1.25 controller factor are common planning figures, not product specifications; follow your battery, inverter and controller manuals, and size cables and fuses for the current. A licensed electrician should connect any system to house wiring. Results are estimates.
Frequently asked questions
What size inverter do I need?
The total watts of everything that can run at once plus about 25%. For loads totalling 480 W, a 600 W inverter.
Can a 1,000 W inverter run a fridge?
Usually, if it is a pure sine wave inverter with enough surge capacity for the compressor to start; check the fridge's data plate.
Does a bigger inverter waste power?
Every inverter draws some idle power, and larger ones usually draw more, so do not oversize it far beyond your loads.
Is BatteryBankCalc free?
Yes, with no sign-up or ads.
Are my loads saved?
Yes, in this browser only.