Solar Panel System Sizing Calculator
Estimate the number of panels and system size needed to meet your electricity demand.
kWh/yr
UK average is ~3,100 kWh/year for a 3-bed home. Check your energy bill.
hr/day
UK average: ~3.0–3.5 hr/day. South-facing roof = 3.8, north = 2.5.
W
%
Accounts for inverter loss, shading, soiling. Typical: 75–85%.
%
% of solar energy used directly (not exported). Typical without battery: 30–50%.
p/kWh
p/kWh
System Estimate
Formulas
- Daily energy needed = Annual kWh / 365
- System kW = Daily kWh / (Peak sun hrs × Efficiency)
- Number of panels = System kW × 1000 / Panel wattage
- Annual generation = System kW × Peak sun hrs × 365 × Efficiency
- Annual saving = (Self-consumed kWh × tariff) + (Exported kWh × export rate)