Path-Q Solar

How much battery capacity is needed to keep essential appliances running overnight?

Answer

Estimate the energy used by the essential loads during the intended backup period, then allow for inverter and battery losses and a reserve. Capacity in kilowatt-hours determines duration, while inverter power in kilowatts determines whether the loads can run simultaneously or start successfully.

Key points

  • List each essential appliance's running watts, startup demand, hours of use, and duty cycle.
  • Calculate energy as power multiplied by operating time, then add a margin for uncertainty and conversion losses.
  • Separate continuous loads such as refrigeration or networking from occasional loads.
  • Check the battery's usable, not merely nominal, capacity and the inverter's continuous and surge ratings.

What it depends on

  • The appliances selected for backup
  • Their actual energy use and startup requirements
  • The desired outage duration and allowable reserve

Risks and trade-offs

  • Oversizing increases cost and may leave capacity unused during normal operation.
  • Undersizing can cause shutdowns or exclude appliances despite adequate energy capacity.
  • Heating, cooling, pumps, and electric water heating can dominate the calculation.

Information you may need

  • An appliance list with wattage or measured consumption
  • Desired hours of overnight backup
  • Battery usable capacity and inverter continuous and surge ratings

Your next step

What to do next

Create a load schedule for essential circuits and ask a qualified provider to size both usable kilowatt-hours and inverter power against that schedule.

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SQ01493