«How many panels do I need?» is everyone’s first question. Here is the three-action method — and the nuances usually forgotten.
Size from consumption, not roof area
- Annual consumption: sum 12 monthly bills. Example: 450 kWh/month → 5,400 kWh/year.
- System size: at ~1,250 kWh per kW per year in the south: 5,400 ÷ 1,250 ≈ 4.3 → take 4.5–5 kW.
- Panel count: with 650 W Kosmo Solar modules: 5,000 ÷ 650 ≈ 8 panels; with compact 450 W ones — 11.
Ready reference
| Home | kWh/year | System | 650 W panels | Roof, m² |
|---|---|---|---|---|
| 100 m² | 4,000–5,000 | 4 kW | 6–7 | ≈ 18 |
| 150 m² | 5,500–7,500 | 5–6 kW | 8–10 | ≈ 25 |
| 200 m² | 8,000–11,000 | 7–9 kW | 11–14 | ≈ 36 |
With an electric boiler or heat pump, multiply the system size by 1.5–2.
Also worth factoring in
- Orientation: south = 100%; SE/SW loses 5–8% — one extra panel compensates;
- an EV adds 2,000–4,000 kWh a year — size the inverter input for it now;
- storage answers «when», panels answer «how much»: for evening use add a battery like the 10 kWh in the P100.
Quick check: system size (kW) ≈ monthly consumption (kWh) ÷ 100. Using 500 kWh a month → about 5 kW.
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