Solar Battery Backup Calculator

Work out how long a solar battery will run essential loads during an outage.

About Solar Battery Backup Calculator

Backup duration depends on the reduced essential load rather than normal consumption. With solar recharging during the day, a modest battery can sustain essentials indefinitely. Whole-home backup needs several times the battery of essential-circuit backup, which is why critical-load panels are standard practice.

Formula

Solar Battery Backup

Backup hours = usable kWh × 1,000 ÷ load in watts

essential load: Reduced load during an outage, not full household consumption

Worked example

With the default values below, Solar Battery Backup Calculator returns Backup Duration of 16.560. Change any input above and every figure here is recalculated in your browser.

Inputs used

Battery capacityminimum 0 kWh: 10 kWh
Usable depth of dischargeaccepts 0–100 %: 90 %
Essential loadminimum 1 W: 500 W
Inverter efficiencyaccepts 0–100 %: 92 %
Solar input during the outageminimum 0 kWh: 12 kWh

Results

Backup Duration: 16.560 h
Days of Cover With Solar Recharging: 999.000 days
Usable Energy: 8.280 kWh
Daily Essential Consumption: 12.000 kWh
Verdict: Solar covers the essential load indefinitely

Step by step

1Values used
2Solar Battery Backup
3Backup Duration= 16.560 h
4Days of Cover With Solar Recharging= 999.000 days
5Usable Energy= 8.280 kWh
6Daily Essential Consumption= 12.000 kWh
7Verdict= Solar covers the essential load indefinitely

Assumptions and limits

The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Solar Battery Backup calculated?

Backup hours = usable kWh × 1,000 ÷ load in watts Backup duration depends on the reduced essential load rather than normal consumption. With solar recharging during the day, a modest battery can sustain essentials indefinitely.

Why does Solar Battery Backup matter?

Whole-home backup needs several times the battery of essential-circuit backup, which is why critical-load panels are standard practice.

What values do I need to enter?

This calculator takes 5 inputs: Battery capacity, Usable depth of discharge, Essential load, Inverter efficiency, Solar input during the outage. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.