How big a system do I need?
Tick what you want to keep running in a power cut, adjust the numbers, and see a rough size for the inverter, the battery and the panels. It is a guide to start a conversation with an installer, not a design.
Rough size
How it works it out
- Inverter: everything ticked could run at once, plus 25% headroom, rounded up to a common size.
- Battery: each item runs for its daily hours or the backup time, whichever is shorter; a fridge runs about a third of the time. Lithium batteries are counted at 90% usable, in units of 5.12 kWh.
- Panels: daily use divided by about 5 sun hours (a fair South African average) and 80% for heat, dust and wiring losses, in panels of about 600 W.
- Leave out the geyser, stove, oven and air-conditioners: they need far bigger systems. A solar geyser or a gas stove is usually cheaper.
Watts are typical values; check the label on your appliance. Motors (pumps, fridges, compressors) draw more for a moment when they start, which the inverter's surge rating covers.