How to Size a Solar System for Your Home, Farm or Business
The single biggest mistake in solar shopping is picking a system by budget instead of by usage. Buy too small and you’ll be back on the grid within a year, wondering why the “solar system” you paid for doesn’t cover your fridge and a kettle at the same time. Buy too big and you’ve paid for capacity you’ll never touch. Here’s how sizing actually works.
Start with your usage, not your roof
Your municipal or Eskom bill tells you roughly how many kWh you use per month. Divide that by 30 and you have a rough daily average. That number — not the size of your roof — is what determines the system you need. A large roof with light usage doesn’t need a 40kW system, and a small home with a borehole pump, pool pump and two aircons might need more than you’d expect.
Three things determine your system size
- Inverter size (kW) — how much power you can draw at once. This is what lets you run an aircon, a kettle and a geyser element simultaneously without tripping.
- Panel array (kW) — how much energy you generate per day. Sized too small, your battery never fully charges, even in good sun.
- Battery capacity (kWh) — how long you can run once the sun goes down or the grid goes out. This is a direct function of your daily usage and how much backup you want.
Home, farm or business changes the answer
A home is usually single-phase and geared around evening and morning peaks — geysers, kitchens, aircons. A farm often needs three-phase power for irrigation pumps and cold storage, plus enough storage to ride out a multi-day outage during harvest. A business needs to keep the doors open during trading hours, which usually means prioritising daytime generation and enough battery to bridge outages without a diesel generator.
The honest way to find your number
A quick calculation from your average bill will get you in the right range, but the only way to get an exact, fully-installed price is a short conversation about your property, your supply type and what you actually want to run during an outage. Use the sizing tool on our homepage for an instant estimate, or send us your latest bill on WhatsApp and we’ll size it properly.