How to Size Your Solar System

Calculate exactly what size solar system you need. Avoid over-spending or under-sizing with this comprehensive guide.

Getting system size right is crucial - too small and you won't meet your needs, too large and you've wasted money. Here's how to calculate the perfect size for your home.

Step 1: Calculate Your Usage

Find your electricity consumption:

Check your Eskom/municipal bill for monthly kWh
Average SA home uses 800-1200 kWh/month
Identify high-use appliances: geyser (40%), pool pump (20%), AC
Note: You may not want to solar everything - prioritize
Calculate daily usage: monthly kWh ÷ 30

Step 2: Size Your Panels

daily Usage	system Size	panels
15-20 kWh	3-4 kW	6-8 x 550W
20-30 kWh	5-6 kW	10-12 x 550W
30-40 kWh	8 kW	14-16 x 550W
40-50 kWh	10+ kW	18-20+ x 550W

daily Usage15-20 kWh

system Size3-4 kW

panels6-8 x 550W

daily Usage20-30 kWh

system Size5-6 kW

panels10-12 x 550W

daily Usage30-40 kWh

system Size8 kW

panels14-16 x 550W

daily Usage40-50 kWh

system Size10+ kW

panels18-20+ x 550W

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Step 3: Size Your Inverter

Inverter sizing principles:

Inverter size = maximum simultaneous load you want to run
Add up wattage of appliances you'll use together
Include startup surge (fridges, pumps need 3x running watts)
Common sizes: 3kW (essentials), 5kW (average), 8kW (large), 10kW+ (full)
Tip: Buy slightly larger inverter for future expansion

Step 4: Size Your Battery

Battery sizing for load shedding:

Calculate backup load: what you need during outage (in watts)
Multiply by hours of backup needed (e.g., 4 hours for Stage 4)
Add 20% buffer (batteries shouldn't fully discharge)
Example: 1000W load × 4 hours = 4kWh × 1.2 = 4.8kWh minimum
Stage 6 areas: consider 10kWh+ for comfortable backup

Price Disclaimer: Prices shown were verified on 29 January 2026. Prices may change without notice. We earn affiliate commissions on qualifying purchases.

All prices are in South African Rand (ZAR) unless otherwise stated. Shipping costs may apply depending on your location.

Battery Sizing Beginner's Guide 5kW Systems

Solar System Sizing Guide FAQs

For a typical SA home (900 kWh/month): 8-10 panels (550W each) for meaningful impact. For essentials only: 6 panels. For full coverage including geyser: 14-18 panels. Calculate precisely using your bill and the sizing steps above.

Slightly oversizing panels (10-20%) is smart - they rarely produce rated output, and extra power feeds battery faster. Oversizing inverter allows future expansion. Oversizing battery gives more backup comfort. The only downside is higher upfront cost.

Major retailers: Builders Warehouse, Makro, Takealot. Solar specialists: SolarShop, Sustainable.co.za, The Solar Warehouse. Always compare prices and check warranty support before buying.

For grid-tied systems, yes - you need a qualified electrician with COC (Certificate of Compliance). For simple off-grid setups, DIY is possible but not recommended. Poor installation is the #1 cause of solar system failures.

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