Solar Panel Savings Estimator — UK Generation & Cost Savings

This estimator calculates how many solar panels can fit on your available roof area, the total system size in kWp, and the expected annual electricity generation based on your UK location and roof orientation.

The calculations

Number of panels = Available roof area ÷ Panel area (m²)

System size (kWp) = Number of panels × Panel wattage ÷ 1000

Annual generation = System kWp × Regional kWh/kWp × Orientation factor

This follows the MCS MIS 3002 method (annual generation = kWp × Kk × shading factor). The regional kWh/kWp (Kk) figures below are derived from MCS / PVGIS irradiance data and are already net of system losses — the standard performance ratio (~0.8, covering inverter, cabling, temperature and soiling losses) is built into the published yield, so no extra loss factor is applied.

UK generation figures (net kWh per kWp per year)

• South England: ~1,050 kWh per kWp per year
• Midlands & Wales: ~950 kWh per kWp per year
• North England: ~900 kWh per kWp per year
• Northern Ireland: ~880 kWh per kWp per year
• Scotland: ~850 kWh per kWp per year

Savings calculation

Your savings come from two sources: electricity you use directly from the panels (saving you the full retail electricity price), and excess electricity exported to the grid under the Smart Export Guarantee (SEG). The self-use percentage depends on your daytime electricity consumption and whether you have battery storage — typically 30-50% without a battery and 70-80% with one.

Smart Export Guarantee (SEG)

We use a default SEG rate of 12p/kWh for exported electricity, reflecting the best flat rates available in 2026 (Octopus Outgoing and OVO around 12p/kWh). Rates are supplier-set and not capped, ranging from around 1p up to about 30p/kWh on time-of-use export tariffs. Check the latest SEG rates from your energy supplier and adjust the rate above to refine your estimate.