Most failed backup systems were sized by guesswork: an inverter that trips when the fridge starts, or a battery that runs flat an hour into an evening outage. Sizing correctly takes four numbers.
1. Running load (kW)
Add up the watts of everything you want on backup at the same time. Typical figures: LED bulb 10 W, TV 100 W, Wi-Fi router 15 W, laptop 65 W, fridge about 150 W while the compressor runs, 12,000 BTU inverter AC about 1,200 W.
2. Peak (surge) load
Motors and compressors draw several times their running power for a moment at start-up. A fridge or pump can surge to about three times its running watts. Your inverter must handle the largest single surge plus everything else already running. Deye's SG04LP1 series, for example, is rated for 2× its rated power for 10 seconds off-grid (Deye datasheet).
3. Energy for the outage (kWh)
Multiply your average load by the hours of backup you want. Appliances do not all run flat out, and fridges cycle on and off, so apply a realistic diversity. Then divide by the battery's usable fraction: for a battery with 95 % DoD, divide by 0.95.
Example: 700 W average evening load × 6 hours = 4.2 kWh. At 95 % DoD and about 95 % inverter efficiency, that is roughly 4.7 kWh nominal, so one 5.12 kWh module such as the Dyness DL5.0F or Deye SE-F5 Plus covers it with a little margin.
4. Solar array (kWp)
If you add panels, divide your daily energy by Uganda's effective sun hours (about 4.5 peak sun hours) and allow roughly 20–25 % for heat, dust, wiring and conversion losses. Keep within the inverter's maximum PV input power and voltage window.
Or let the configurator do it
Battery World's Find My System tool runs these calculations as you pick appliances, then recommends Deye, GoodWe and Dyness-based systems using compatibility published by the manufacturers.
Size your own system
Run Find My System with your appliances and get three matched options.