What Size Solar Battery Do I Need for Load Shedding?

Buy too small a battery and it runs flat halfway through load shedding. Buy too big and you have spent money you did not need to. Getting battery size right is about matching capacity to what you actually want to keep running, and for how long.

Step 1: List your backup loads

Decide what must stay on during an outage and find each appliance's power draw in watts:

• Lights, Wi-Fi router, TV and laptop chargers: usually 200 to 400 watts combined.
• Fridge and freezer: roughly 150 to 300 watts on average over time.
• Heavy appliances like kettles, microwaves, geysers and pool pumps: 1,500 to 3,000 watts each.

The essentials add up to far less than people expect. It is the high-draw appliances that drain a battery quickly.

Step 2: Multiply by the hours you need

Battery capacity is measured in kilowatt-hours (kWh), which is simply power multiplied by time. If your essential loads average 500 watts (0.5 kW) and you want four hours of backup, you need about 2 kWh of usable energy for that block. Most South Africans size for back-to-back stages, which is why 5 to 10 kWh is the common sweet spot.

Step 3: Allow for real-world losses

Add a margin for inverter losses and the fact that you should not run a battery completely flat every cycle. A practical rule is to size your usable capacity about 20 to 30 percent above your calculated need. Modern lithium batteries allow deep discharge, but a buffer extends their life.

A quick reference

• Just the essentials through normal load shedding: around 5 kWh.
• Essentials plus occasional heavy use across longer stages: around 10 kWh.
• Running most of a larger home overnight: 15 kWh or more.

Use our system size calculator to turn your own usage into a capacity estimate.

Remember the inverter and recharge time

Your inverter limits how much you can run at once, and your panel array determines how fast the battery refills between outages. All three need to be balanced. For a tailored design, get free quotes from verified installers.