Inverter Size Calculator South Africa
Determine the right inverter size for your home or business
This calculator provides estimates. Consult a qualified solar installer for a proper assessment and SANS-compliant installation.
Frequently Asked Questions
What size inverter do I need?
Add up the running watts of all appliances you want to power during loadshedding, add 20% headroom, and ensure surge capacity for motor-driven appliances like fridges.
Do I need a hybrid or off-grid inverter?
Hybrid inverters connect to both the grid and batteries, charging from solar. Off-grid inverters work only with batteries and solar. Most SA homes need hybrid.
What is the difference between VA and Watts?
Watts = VA × power factor. For resistive loads (lights, heaters), VA ≈ Watts. For inductive loads (motors, fridges), VA can be 1.5-2x Watts. Always size by Watts.
This calculator provides estimates. Consult a qualified solar installer for a proper assessment and SANS-compliant installation.
How the inverter sizing calculator works
Two separate numbers decide the inverter. The **power rating** must exceed the peak load that runs at the same time — a kettle, a microwave and a geyser together are a different machine from lights and a router. The **battery** must hold the energy for the hours you want to run.
600 W for 4 hours needs 2400 Wh at the load, which at 90% efficiency is 2667 Wh of battery — and at 90% depth of discharge, a battery of 2963 Wh, or about 2.96 kWh.
The inverter itself should be rated above the peak: a 600 W steady load with a 2 000 W kettle starting means a 3 kW inverter, not a 1 kW one — unless the kettle is on a non-backed-up circuit.
What changes the answer in South Africa
In South Africa most household backup systems are 3 kW or 5 kW hybrid inverters with 5 kWh of lithium storage, because that is the size that runs lights, router, TV and fridge through a stage 4 slot. Geysers, stoves and pool pumps are usually left off the backup circuit — they are the reason systems are oversized and expensive.
Common questions about the inverter sizing calculator
Do I size the inverter on watts or on kWh?
Both, for different reasons: watts decide the inverter rating (peak simultaneous load), kWh decides the battery (energy over hours).
Can I run a geyser on an inverter?
Technically yes, practically no. A 4 kW element alone needs an inverter bigger than most household systems, and it will flatten the battery in under an hour.
What size inverter for a normal house?
3 kW covers lights, router, TV and a fridge; 5 kW adds a microwave and a few small appliances. Start from the 600 W measured load, not from the house size.