What size inverter and battery does your home need?
The inverter is sized by what runs at the same time, the battery by how long it must last. Work out both in three steps, with typical appliance loads and a battery table.
Updated 2 November 2026 · sources at the end of the page
The short answer
An inverter is sized by what must run at the same time, in kilowatts. A battery is sized by how long it must run, in kilowatt-hours. For most homes that want lights, the fridge, Wi-Fi, the TV and a few plugs on during an outage, a 5 kW hybrid inverter with 5 to 10 kWh of lithium battery is a common starting point. Add a borehole pump, a kettle or cooking and you are looking at 8 kW or more.
Outages have replaced load shedding
Load shedding came in announced two- and four-hour blocks, so people sized batteries for the length of a stage. Today's outages come from failed substations, cable theft and municipal faults. They arrive without a schedule and can last much longer.
South Africans have noticed. Google searches for "power outage" were 130% higher in the 13 weeks to 1 November 2026 than in the same weeks of 2025. Over the same 12 months, searches for "load shedding" fell 87% and searches for "inverter and battery" rose 60%. Size the battery for an outage of unknown length, with panels to refill it if you can.
Step 1: list what must stay on
Walk through the house and write down what you would miss in the first hour of an outage. These are typical ratings; the label on each appliance gives the real number.
| Appliance | Typical power draw |
|---|---|
| LED lights, 10 bulbs | 100 W |
| Fridge-freezer (running) | 100–200 W |
| Wi-Fi router and fibre box | 15–25 W |
| TV and decoder | 100–150 W |
| Laptop | 50–90 W |
| Alarm and gate motor (standby) | 20–50 W |
| Borehole pump | 750–1 500 W |
| Microwave | 900–1 200 W |
| Kettle | 2 000–2 400 W |
| Stove plate or oven | 1 500–3 000 W |
| Geyser element | 2 000–4 000 W |
Motors in fridges and pumps draw several times their running power for a moment when they start. The inverter has to handle that surge as well as the steady load.
Step 2: size the inverter
Add up the loads that could run together, then add about 25% headroom for start-up surges and the things people forget. That number in kilowatts is your minimum inverter size.
- Around 5 kW: lights, fridge, Wi-Fi, TV, laptops, alarm and gate. A common size for home backup.
- 8 kW and up: add a borehole pump, microwave or kettle, or a bigger household that runs more at once.
- Three-phase or more than one inverter: large homes, farms and workshops with three-phase supply.
A hybrid inverter is one unit that takes solar panels, a battery and the grid. It switches to the battery when the supply drops and lets you add panels later without replacing anything.
Step 3: size the battery
Battery size in kWh = average load in kW × hours of backup ÷ 0,9. The 0,9 allows for the roughly 10% of a lithium iron phosphate battery's capacity that is normally kept in reserve. The table shows the battery needed for three levels of load:
| Average load during an outage | 4 hours | 8 hours | 12 hours |
|---|---|---|---|
| 300 W (Lights, fridge, Wi-Fi) | 1,3 kWh | 2,7 kWh | 4,0 kWh |
| 500 W (Plus TV, laptops, alarm) | 2,2 kWh | 4,4 kWh | 6,7 kWh |
| 1 000 W (Plus a pump or more people at home) | 4,4 kWh | 8,9 kWh | 13,3 kWh |
Many lithium batteries come in modules of about 5 kWh that can be stacked, so you can start with one and add another later if the inverter supports it.
What to keep off the backup circuit
The geyser, stove, oven, kettle and pool pump draw kilowatts each. Putting them on the backup circuit means a much bigger inverter and battery for a few minutes of use. Most installations wire only the essential circuits to the inverter. For hot water, a solar geyser or heat pump takes the largest single load off the account. For cooking, gas covers the outage.
Backup only, or backup and savings?
A backup-only system charges its battery from the grid. It keeps you running but does not lower the bill. Add panels and the same system recharges from the sun, carries you through longer outages and cuts the account every sunny day. The savings calculator estimates the panel side from your bill.
We install equipment from brands such as Deye, Sunsynk and Freedom Won, chosen for the job. A grid-connected system also has to be registered with Eskom or your municipality; our registration guide explains what applies.
Sources
What size inverter do I need for my house?
Add up everything that must run at the same time during an outage and leave about 25% headroom. Lights, fridge, Wi-Fi, TV and a few plugs usually fit a 5 kW inverter. Add a borehole pump, kettle or oven and most homes need 8 kW or more.
How long will a 5 kWh battery last?
A lithium battery delivers roughly 90% of its rated capacity, so about 4,5 kWh. Running 500 W of essentials, that is about 9 hours. At 1 000 W it is about 4,5 hours.
Can an inverter and battery run my geyser?
It can, but it drains the battery fast because a geyser element draws 2 to 4 kW. Most homes keep the geyser off the backup circuit and heat water with a solar geyser or heat pump instead.
Do I need solar panels with my inverter and battery?
Not for backup alone, because the battery can charge from the grid. Panels recharge it during the day, carry you through longer outages and cut the electricity bill. A hybrid inverter lets you add them later.
Do I need to register an inverter and battery system?
If it is connected to your distribution board and the grid, NERSA says grid-connected systems up to 100 kW must be registered with Eskom or the municipality. See our guide to registering rooftop solar.
Get a backup system sized for your house
It opens as a WhatsApp message to Mari Louise with a reference number, so the first call is about your site instead of the basics.
Rather talk? Call the office on 017 004 0001 or WhatsApp 072 326 0268.