The battery bank installed in the main PV system has eight 12 V, 97.6 Ah batteries. This system is not designed to run major loads—such as the home’s air conditioner—during a power outage. But if the battery bank is cycled down to 20% state of charge (80% depth of discharge), it can provide about 6.7 kWh to the critical loads, assuming an inverter efficiency of 90%.
For example, during stormy weather, this could provide three days of backup for an energy-efficient refrigerator (1.2 kWh/day), plus a handful of compact fluorescent lights (5 x 15 W x 5 hrs./day = 375 Wh/day) and a TV (130 W x 5 hrs./day = 650 Wh/day). With sunny skies, their 2.8 kW PV (flat/north facing) system could increase the energy available by about 8.2 kWh per day.