Measure daily energy first
A plug-in energy meter used over a representative full day gives a useful starting point. Warm rooms, frequent door opening, defrost cycles and loading warm food can increase consumption. An annual energy label gives an estimate, but your conditions may differ.
Convert kilowatt-hours to watt-hours by multiplying by 1,000. A refrigerator using 1.2kWh per day consumes about 1,200Wh per day, averaging 50W across its cycles.
Illustrative capacity budget
| Backup window | Load energy at 1.2kWh/day | Nominal battery at 85% efficiency, 20% reserve |
|---|---|---|
| 8 hours | 400Wh | About 588Wh |
| 12 hours | 600Wh | About 882Wh |
| 24 hours | 1,200Wh | About 1,765Wh |
| 48 hours | 2,400Wh | About 3,529Wh |
Check compressor startup
The starting requirement can be higher than the running demand. Check appliance documentation and power-station compatibility guidance. Where needed, use an appropriate inrush measurement by a competent person. A basic energy meter may not capture the short peak.
Also account for other devices already using the inverter when the compressor starts. Surge output is time-limited and is not a substitute for continuous output.
Add the other essentials
A router using 20W adds 480Wh over a day. Lights and charging add more. This is why a station that supports a refrigerator alone can fall short when used for an entire household’s essentials.
Use the calculator with average refrigerator watts for energy sizing. Enter running and startup power separately. Never use the 50W average from the example as the compressor’s startup requirement.
Choosing between battery sizes
A smaller unit can cover a short interruption if it starts the compressor. More capacity extends runtime, while compatible solar can replace part of the energy during daylight. Expansion batteries are useful only on supported systems.
The HomePower 3000 guide includes calculated examples for a 3,072Wh system. Treat those examples as estimates, not measured refrigerator tests.
Test the complete setup
Run a supervised trial with the exact refrigerator, cable and station before an outage. Confirm startup, repeated compressor cycles and any automatic shutdown behavior. Keep ventilation clear and follow both manuals. Food safety depends on actual refrigerator temperature, not the battery display alone.