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How Many Solar Panels and Batteries Does a House Need?

Panels and batteries are sized from your electricity use. This guide shows the simple calculation with a worked example. The Sun Pays has supplied solar equipment since 2007 and sells from Rayton, Pretoria.

For a longer South African home guide, read How Many Solar Panels Do I Need? and How Long Will a 5kWh Lithium Battery Last? Questions about sizing or the calculator? See the solar calculator FAQ.

Step 1: Find your daily use in kWh

Look at your electricity bill for your monthly kWh and divide by 30. For example, 600 kWh a month is about 20 kWh a day. Not on the bill? Add up each appliance's watts times the hours it runs.

Step 2: Size the solar panels

Much of South Africa gets roughly 5 to 6 hours of strong sun a day, and less in winter. A rough rule is: daily kWh divided by sun hours, then divided by 0.8 to allow for system losses. For 20 kWh a day at 5 sun hours: 20 / 5 / 0.8 = 5kW of panels. With 630W panels, that is about 8 panels (8 x 630W = 5.04kW). This is an example, so check your own numbers.

See the 630W Deichmann bifacial N-type solar panel and our solar panel range. Do not forget panel mountings.

Step 3: Size the batteries

Batteries cover what you use when the sun is down and during outages. Take the kWh you want to run from batteries, then allow for usable capacity. For example, to run 10 kWh overnight on lithium batteries you would want about 12 kWh of battery to leave a safety margin. One 51.2V 100Ah battery stores 5.12kWh, so that is about 2 to 3 batteries.

Browse lithium batteries, including the TheSunPays 51.2V 100Ah 5.12kWh battery.

Step 4: Match the inverter

The inverter must handle your peak load and be compatible with the battery voltage. Read What size solar inverter do I need?

Frequently asked questions

How many panels does an average home need?

It depends on use. Many homes fall between 4 and 12 panels. Work it out from your kWh using the steps above, or use the sizing calculator.

Do I need batteries?

Only if you want power at night or during outages. Without a battery, a system that depends on the grid will shut down when the grid fails.

Can I start small and expand?

Yes. Panels, batteries and some inverters can be added later. Choose parts that can be expanded, such as batteries that connect in parallel.