Quick estimate mode — for battery storage, export tariffs, roof orientation and detailed ROI:
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Quick Solar Panel Calculator
Enter your annual electricity use and location to get system size, output and payback.
Your Home
Check your electricity bill. Average home: 3,000–5,000 kWh/year.
Peak sun hours per year for your region.
Your current rate. Check your bill.
Typical installed cost: £6,000–£12,000 for 10–16 panels.
Result
Panels needed
–
panels
Payback
–
years
Assumes 80% self-consumption. Export tariffs, battery storage and grants can improve payback further.
Need battery, export tariff and roof area?
Full calculator covers orientation, shading, battery sizing and detailed 25-year ROI.
How to calculate solar panel system size
The formula
System size (kW) = annual usage (kWh) ÷ peak sun hours. Panels = ⌈system kW × 1000 ÷ panel wattage⌉.
What are peak sun hours?
Peak sun hours represent the equivalent number of hours per year when solar irradiance averages 1,000 W/m². Northern Europe gets ~800–950 h, southern Europe ~1,300 h, and tropical regions up to 1,900 h.
How much roof space do I need?
A standard 400 W panel is roughly 1.7 m² × 1.0 m = 1.7 m². Ten panels need about 18–20 m² of clear roof area, ideally south-facing with less than 30° pitch.
Pro tip: Get at least three installer quotes — prices vary significantly. Check for government grants or feed-in tariffs in your country before committing to a system size.