Outage Simulator: How Long Will Your House Run?
Pick a battery, switch your loads on and off, and see how long the lights stay on. Turn off the air conditioner and watch the hours come back.
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How to use the simulator
Start by switching off everything you would not need in an outage, then add things back one at a time and watch the runtime. Two numbers matter, and they answer different questions:
- Energy (kWh per day) decides how long the battery lasts.
- Power (kW at once) decides whether the battery can run those loads at all, and whether it can start motors.
The appliance figures are typical values. If you know the real wattage from a nameplate or a plug-in meter, use the edit button on any row to replace ours.
What the simulator assumes
- The battery starts full and the outage begins at 6 pm, so solar has no chance to help until the next morning.
- Loads are spread evenly through the day. Real homes are lumpier, so treat the result as a planning number rather than a promise.
- Ninety percent of stored energy reaches your outlets after inverter losses, and a reserve is held back.
- Only one motor starts at a time.
Want the simulator loaded with your own appliances and usage?
Build My Power Plan →Common questions
It depends almost entirely on what you leave on. Essentials such as a refrigerator, lights, internet and a few outlets often use 4 to 8 kWh a day, which a 13.5 kWh battery can carry for a day or two. Add central air conditioning and the same battery may last well under half a day. Use the simulator above with your own loads.
A central air conditioner draws roughly 3 to 5 kW while running. A refrigerator averages well under a tenth of that. Over a hot day, cooling can use more energy than everything else in the house combined, so removing it often doubles or triples runtime.
Starting is a separate question from running. A compressor needs a brief surge several times its running power. If that surge is more than the inverter can deliver, the unit will not start even with a full battery. A soft-start device, a larger inverter or a second battery are the common fixes, and an installer should confirm which applies.
Only if the system is built for it. Standard grid-tied solar shuts off when the grid goes down. With a battery or other backup equipment designed to form its own grid, solar can keep running and recharge the battery. Output drops sharply in cloudy or stormy weather, which is why the simulator lets you choose the weather.