Path-Q Solar

What energy losses should I include when sizing a solar battery?

Answer

Include losses when charging the battery, discharging it, converting between AC and DC, and operating standby controls. Use the system's tested round-trip or delivered-efficiency data rather than assuming all solar energy reaches the loads.

Key points

  • Charging and discharging are not perfectly efficient.
  • Inverter, transformer, wiring, and battery-management electronics consume energy.
  • Standby consumption matters during long periods of backup or low demand.
  • Solar production may also be curtailed when the battery is full or charging power is limited.

What it depends on

  • Whether the system is AC-coupled or DC-coupled
  • Battery and inverter efficiency at the relevant power level
  • Standby consumption and operating mode
  • Charging limits, temperature, and expected solar surplus

Risks and trade-offs

  • Ignoring losses can lead to an undersized battery or unrealistic backup-duration estimate.
  • Oversizing to cover every loss can increase cost without improving useful resilience.
  • Short, high-power loads may be limited by power rating even when sufficient stored energy remains.

Information you may need

  • Battery usable capacity and round-trip efficiency
  • Inverter efficiency and standby consumption
  • Expected daily load, peak load, and desired backup duration
  • Whether solar will recharge the battery during an outage

Your next step

What to do next

Create an energy budget showing solar input, charging losses, storage, discharge losses, and load consumption under normal and outage operation.

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