This is an assumed one-day backup calculation, not measurements from a real home. Loads are explicit so the example can be recalculated.
Model loads
Assume communications at 20 W for 24 hours, ventilation at 40 W for 24 hours, lighting at 30 W for 5 hours and refrigeration at an assumed 0.8 kWh per day. Heating and hot water are excluded.
Energy balance
E = Σ(P × t)/1000 gives 0.48 + 0.96 + 0.15 + 0.80 = 2.39 kWh over 24 hours. Backup equipment self-consumption is excluded and must be added for actual selection.
Battery
Assuming efficiency 0.90 and usable fraction 0.80 gives 2.39/(0.90×0.80) = 3.32 kWh nominal. This is a preliminary scenario without ageing, temperature derating or extra margins.
Power and restoration
The refrigerator’s daily energy does not define its starting demand. Check inverter, BMS and peak simultaneity separately, plus charging time before the next outage.
Limits and application
PV is excluded, so sunny weather is not a hidden assumption. Real loads may include a pump or medical equipment with different requirements; this example does not cover them.
| Item | Parameter | Check / result |
|---|---|---|
| Communications + ventilation | 0.48 + 0.96 kWh | 1.44 kWh |
| Lighting + refrigerator | 0.15 + 0.80 kWh | 0.95 kWh |
| Total | 24 h | 2.39 kWh |
What this means for your project
Replace assumed loads with measurements and add system self-consumption. Final selection needs starting, protection and repeated-outage reserve checks.
Sources and scope of review
Related reading
- Heat Pumps in Low-Energy Homes
- How to Size a Home Battery
- How to Choose an Inverter for Backup Power
- PV plus Battery: How a Hybrid System Works