Guide, updated August 2026
How many panels does a 3-bedroom flat need?
A worked example from real appliance load, with the panel count, battery size and inverter rating you actually need.
A standard three-bedroom flat in Lagos needs about 3.5kVA of inverter, 7kWh of usable battery and six 550W panels. Here is the arithmetic, so you can adjust it for your own load.
Step 1: list what actually runs
| Appliance | Watts | Hours/day | Wh/day |
|---|---|---|---|
| 12 LED lights | 108 | 6 | 648 |
| Fridge/freezer | 150 average | 24 cycling | 1,800 |
| 4 standing fans | 240 | 8 | 1,920 |
| TV and decoder | 120 | 5 | 600 |
| Laptops, phones, router | 150 | 6 | 900 |
| Water pump | 750 | 0.5 | 375 |
| One AC, 1HP inverter type | 750 | 6 | 4,500 |
That is roughly 10.7 kWh a day. Without the AC it is about 6.2 kWh, which is why the AC decision changes the system more than anything else on the list.
Step 2: size the panels
Lagos gives about 4.5 usable peak sun hours a day on an average annual basis. Allow 20 percent for temperature derating, soiling and conversion loss. To make 10.7 kWh you need about 10.7 ÷ 4.5 ÷ 0.8 = 3.0 kWp, which is six 550W panels at 3.3 kWp. That is roughly 12 square metres of roof.
Step 3: size the battery
You need to carry the evening and overnight load, which is typically 60 to 70 percent of daily consumption. That is about 7 kWh usable. On LiFePO4 at 90 percent depth of discharge, a 7kWh nameplate pack is right. Do not accept a lead-acid equivalent quoted at the same nameplate figure; usable capacity is roughly half.
Step 4: size the inverter
The inverter is sized on peak simultaneous load, not daily energy. Fridge compressor, pump start and AC start can coincide. 3.5kVA covers this flat comfortably. If you run two ACs you are at 5kVA and a bigger battery.
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