How to Calculate What Size Solar System You Need for Your Home
Stop guessing. This step-by-step guide will tell you exactly how much solar power your home needs — and what it’ll cost.
One of the most common mistakes South Africans make when going solar is buying a system that’s too small (and being frustrated when it can’t handle the load) or too large (and overpaying unnecessarily).
The right system size is personal — it depends on your appliances, your habits, and your goals. This guide walks you through the calculation in plain language, no engineering degree required.
Step 1: List Your Appliances and Their Wattage
Start by writing down every appliance you want to power during load shedding or off-grid hours. Then find the wattage for each one (usually printed on the appliance or in the manual).
Here are typical wattages for common South African households:
| Appliance | Typical Wattage |
|---|---|
| LED bulb | 5–10W |
| CFL bulb | 15–25W |
| Ceiling fan | 50–75W |
| Wi-Fi router | 10–20W |
| Smart TV (43″) | 80–120W |
| DSTV decoder | 15–30W |
| Laptop | 45–90W |
| Desktop PC | 150–300W |
| Mini Hi-Fi / speakers | 30–100W |
| Bar fridge | 100–150W |
| Full-size fridge | 150–300W |
| Chest freezer | 100–250W |
| Microwave (900W) | 900–1200W |
| Electric kettle | 1500–2200W |
| Washing machine | 500–2000W |
| Air conditioner (1.5 ton) | 1200–2000W |
| Water pump | 500–1500W |
| Pool pump | 750–2000W |
Step 2: Calculate Your Daily Energy Usage
For each appliance, multiply the wattage by the number of hours you use it per day. This gives you Watt-hours (Wh).
Example household calculation:
| Appliance | Watts | Hours/Day | Daily Wh |
|---|---|---|---|
| 8 x LED bulbs | 60W total | 5 hrs | 300Wh |
| Wi-Fi router | 15W | 8 hrs | 120Wh |
| TV (43″) | 100W | 4 hrs | 400Wh |
| Fridge | 200W | 24 hrs* | 480Wh* |
| Laptop | 65W | 6 hrs | 390Wh |
| TOTAL | 1,690Wh/day |
*Fridges cycle on and off — they typically only run about 40% of the time, so a 200W fridge uses roughly 200W × 24hrs × 0.4 = 1,920Wh… but for simplicity above we used a daily average of 480Wh.
Your daily total in this example: ~1,700Wh or 1.7kWh
Step 3: Size Your Battery Bank
Your battery needs to store at least one full day’s usage (more if you want cloudy-day backup).
Formula:
Daily Wh ÷ Battery Voltage ÷ Usable Depth of Discharge = Amp-hours (Ah) needed
Using our example:
- Lithium battery at 24V, 85% usable: 1,700 ÷ 24 ÷ 0.85 = ~83Ah
- A 100Ah 24V lithium battery would cover this comfortably
For lead-acid at 50% usable: 1,700 ÷ 24 ÷ 0.5 = ~142Ah → you’d need at least a 150Ah lead-acid battery
Step 4: Size Your Solar Panels
Solar panels need to recharge your batteries within the available sun hours. South Africa gets approximately:
- Durban/KZN: ~4.5 peak sun hours/day
- Johannesburg/Gauteng: ~5.5 peak sun hours/day
- Cape Town: ~5.0 peak sun hours/day (less in winter)
- Northern Cape/Limpopo: ~6.0–6.5 peak sun hours/day
Formula:
Daily Wh needed ÷ Peak sun hours × 1.25 (efficiency factor) = Solar panel wattage needed
Using our example in Durban:
1,700 ÷ 4.5 × 1.25 = ~472W of solar panels
So two 250W panels or one 500W panel would cover this household’s needs on a sunny day.
Step 5: Size Your Inverter
Your inverter needs to handle the peak simultaneous load — i.e., everything running at the same time. This is usually higher than your daily average.
In our example, if you turned everything on at once: 60W + 15W + 100W + 200W + 65W = 440W peak
A 1000VA (1kVA) inverter handles this with headroom to spare.
Rule of thumb: Your inverter’s VA rating should be at least 20–25% higher than your peak load to avoid overloading it.
Quick System Sizing Summary
| Household Size | Typical Daily Usage | Recommended System |
|---|---|---|
| Small (lights, router, TV) | 500–1,000Wh | 1kVA inverter, 100Ah lithium, 2x200W panels |
| Medium (+ fridge, laptops) | 1,500–3,000Wh | 3kVA inverter, 200Ah lithium, 4x400W panels |
| Large (full home) | 5,000–10,000Wh | 5–8kVA inverter, 400–600Ah lithium, 8–12x400W panels |
What Will It Cost?
Here’s a rough guide for 2026 South African pricing:
| System Size | Approximate DIY Cost | Approximate Installed Cost |
|---|---|---|
| Small (1kVA) | R12,000 – R18,000 | R20,000 – R30,000 |
| Medium (3kVA) | R30,000 – R50,000 | R50,000 – R80,000 |
| Large (5kVA) | R60,000 – R90,000 | R90,000 – R140,000 |
Remember: the Section 12B solar tax incentive allows you to claim 25% back on panel costs (up to R15,000), reducing your effective spend.
Get Your Components at SunProfit
Now that you know what you need, browse our full range of solar components:
👉 Shop Solar Panels 👉 Shop Inverters 👉 Shop Batteries
Want us to do the calculation for you? Send us your monthly electricity bill on WhatsApp and we’ll size your ideal system for free.
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