Blackout Runtime Calculator

List your critical loads and see how long the battery left at the start of a blackout keeps them running.

This estimates how long a home battery or power station keeps your critical loads running in a blackout, using the method in Solar Battery Backup: What Can You Run During a Blackout? The example rows are that guide's critical-load list, so edit or remove them. Everything is worked out in your browser. Nothing is saved or sent anywhere.

1. Critical loads

Enter watts and hours a day, or leave those blank and enter Wh a day directly, for example from an energy rating label (kWh a year × 1,000 ÷ 365).

2. Your battery

Not the battery's full size, unless it's full. If you keep a backup reserve, use that.
Inverter losses and the system's own use (0 to 50%).
From your inverter's specification. 0 to skip.
For example kettle plus microwave plus fridge. 0 to skip.

3. Results

How it was worked out

    Before you rely on it

    • A grid-connected system only runs in a blackout if it has a backup function and the backup output is wired to your circuits. Check what your system does, and which circuits are backed up.
    • This assumes the panels can't recharge the battery during the blackout. Some systems can. Ask your installer.
    • Big heating and cooling loads change the answer completely. Run big appliances one at a time.
    • If anyone relies on powered medical equipment, talk to the equipment provider and your electricity retailer about a plan. Don't rely on a home battery alone.
    • Never connect a power station or generator to your home's wiring through a power point or a home-made lead. It needs an approved inlet and changeover switch installed by a licensed electrician.
    • This is a planning estimate only, not a system design, wiring specification or safety assessment. Check the data sheets and manuals for your battery, inverter and charge controller.
    • Safety: in Australia, any work on 240V AC wiring, including connecting an inverter, battery or solar system to a home's switchboard or fixed wiring, must be done by a licensed electrician. Grid-connected systems also need approval from your electricity network.

    Next steps

    Read the full guide in Solar Battery Backup: What Can You Run During a Blackout? Planning a power station instead? Try the Power Station Runtime Calculator at Wired For The Wild.

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