How to Size a Solar Inverter and Battery for Load Shedding
Please note: this guide was written with the help of AI and may contain mistakes or outdated information. It is general information only. Always do your own research (DYOR): check product specifications with the manufacturer, and use a qualified professional for any electrical, security or gate installation.
Buying an inverter and battery that are too small means lights that cut out the moment the kettle goes on. Buying too big means paying for capacity you never use. Sizing it properly takes four steps and a pen and paper.
Step 1: List what you want to keep running
Write down every appliance you want powered during a power cut, with its wattage (printed on the label or in the manual). Typical essentials are lights, the fridge, the Wi-Fi router, the TV and phone chargers. Heavy loads such as geysers, stoves, ovens and kettles use a lot of power, so decide honestly whether they need to run on batteries.
Step 2: Find your peak power (this sets the inverter size)
Add up the watts of everything that could run at the same time. That total is your peak load. Motors in fridges, freezers and pumps draw extra power for a moment when they start, so allow headroom. As a rule of thumb, choose an inverter whose continuous rating is comfortably above your peak load rather than just matching it.
Example only: lights 200 W + fridge 150 W + router and TV 150 W + laptop 100 W = about 600 W. A small home like this is looking at a hybrid inverter in the low-kilowatt range, while a house that adds a kettle or microwave needs a bigger one.
Step 3: Work out your energy use (this sets the battery size)
Multiply each appliance’s watts by the hours it will run to get watt-hours, and add them up. Then think about how long a typical outage lasts. If your essentials use 600 W and you want to cover a 4-hour outage, you need roughly 2,400 Wh, or 2.4 kWh, of usable battery.
Batteries are quoted in kWh, or in amp-hours at a voltage. To compare them, multiply volts by amp-hours and divide by 1,000. For example, a 48 V, 100 Ah battery stores about 4.8 kWh.
Step 4: Add a safety margin
Inverters and batteries lose some energy as heat, and you will not want to drain a battery completely every time. Add roughly 20% to your energy figure, and allow for growth if you may add appliances later. If you want to run more of the house, or cover longer outages, size up from here.
Don’t forget the rest of the system
- Solar panels: panels recharge the battery during the day. See our solar panels and roof mounting kits.
- Protection: fuses, breakers and DC combiner boxes protect the wiring and battery. Browse protection.
- Housing: battery cabinets and brackets keep lithium batteries neat and safe. See battery cabinets.
- Installation: have the system installed by a qualified installer and ask for the Certificate of Compliance (CoC).
Ready to choose?
Once you know your peak load and the energy you need, browse our inverters and solar batteries. If you are not sure, get in touch and we will help you check your numbers before you buy.
AI-assisted content. Please do your own research (DYOR) before you buy or install.