Path-Q Solar

How should I size a home battery and inverter for the circuits I want to keep running during an outage?

Answer

Size the inverter for the selected circuits' simultaneous and startup power, and size the battery for their energy use over the intended outage duration, allowing for usable-capacity limits and reserve. Solar or another recharge source is material if you want to support multi-day or repeated outages, but it is not necessarily required for a defined outage period that begins with a sufficiently charged battery.

Key points

  • Separate continuous power, peak power, and motor or compressor startup demand.
  • Battery kilowatt-hours determine duration; inverter kilowatts determine what can run at once.
  • Critical-load panels can avoid sizing backup equipment for the entire home.

What it depends on

  • Selected circuits and appliance loads
  • Startup characteristics of pumps, refrigerators, HVAC, and other motors
  • Desired outage duration and weather conditions
  • Battery usable capacity, inverter rating, and recharge capability

Risks and trade-offs

  • Including electric heating, cooking, or water heating can greatly increase required power and energy.
  • A system that supports one appliance individually may not support several simultaneously.

Information you may need

  • Circuit schedule and appliance power data
  • Required backup duration
  • Inverter surge rating and battery usable capacity
  • Installer's load calculation and backup wiring design

Your next step

What to do next

Create a critical-load list and ask for a written calculation showing continuous load, startup load, battery duration, and recharge assumptions.

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