How to size a backup system without guessing

Start with the essential-loads list, then measure it. A clamp meter on the distribution board for a normal evening gives you a better number than any appliance table.

Second, decide the outage you are designing for. Four hours and four days produce very different systems; most residential customers need four hours, and most sales conversations quietly assume four days.

Third, check the surge. A borehole pump draws three to five times its rated current for under a second, and that number sets the inverter, not the battery.

Fourth, check the recharge path. If the grid returns for three hours a day, the charger must replace the nightly kWh in that window — otherwise the system degrades quietly over a week.