Backup time is roughly the battery’s usable energy divided by the power your loads draw. A 5.12 kWh battery running 500 W of loads would last about 8 hours, if you plan on using about 80% of its capacity.
The simple formula
Hours of backup ≈ (battery kWh × usable share) ÷ load in kW
Planning with about 80% usable capacity leaves margin for inverter losses and battery protection. Your installer will use the exact figures for your equipment.
Worked examples with a 5.12 kWh Prime battery
| Load running | Approximate backup |
|---|---|
| 250 W | about 16 hours |
| 500 W | about 8 hours |
| 1,000 W (1 kW) | about 4 hours |
| 2,000 W (2 kW) | about 2 hours |
These are planning estimates. Real backup depends on what is switched on, battery temperature and age, and whether solar is charging at the same time.
How do I find my load?
Check the wattage on appliance labels for what you want to run during a cut, and add them up. Motors and compressors (pumps, fridges, air conditioners) draw more when starting; your installer checks the inverter can handle that.
Choose a size
Prime batteries come in 2.56, 5.12, 10.24 and 16.07 kWh. Use the Tenzor solar calculator’s Hybrid option for a suggested size.
FAQs
Does solar extend backup during the day?
Yes. With a hybrid inverter, solar can run loads and charge the battery while the grid is down.
Can I add batteries later?
Often yes, within the inverter and battery system’s limits. Plan this with your installer.