The total active power of backup loads decides the maximum sustainability of the FHP system in backup mode.

The longest backup time required by the customer can be obtained by analyzing the total active power of the home backup loads.

For example, if the total active power of all backup loads is 3kW, then the maximum sustainable backup time for the household is 13.6kWh/3kW≈4.5h when the only FHP source is a single aPower X fully charged (SOC=100%). It can be seen that the smaller the total active power, the longer the backup time.