How many solar panels do I need for a typical UK home?

A typical UK household uses around 3,500-4,000 kWh per year. With a south-facing roof in southern England, a 4 kWp system (10 x 400W panels) would generate roughly 4,000-4,400 kWh annually. Homes with higher usage or less optimal orientations may need more panels.

What is the best roof orientation for solar panels in the UK?

Due south is optimal, generating the maximum annual output. South-east and south-west orientations lose only about 5% output. East or west-facing roofs lose around 20%. North-facing roofs are generally not recommended as they lose 40-50% of potential output.

What is self-consumption and why does it matter?

Self-consumption is the percentage of solar generation you use directly rather than exporting. Since you save the full electricity rate (around 24.5p/kWh) on self-consumed energy but only receive the export tariff (around 5.5p/kWh) for exported energy, higher self-consumption significantly improves financial returns. Battery storage and smart scheduling can increase self-consumption from a typical 30-50% to 70-90%.

How much roof area do solar panels need?

A standard 400W panel is approximately 1.75 m² (about 1.0m x 1.75m). A typical 4 kWp system of 10 panels needs around 17.5 m² of usable roof space. You also need to account for obstructions like chimneys, roof windows, and ventilation pipes.

What is the Smart Export Guarantee (SEG) rate?

The Smart Export Guarantee requires licensed electricity suppliers with 150,000+ customers to offer a tariff for exported solar electricity. Rates vary by supplier and tariff type, typically ranging from 3p to 15p per kWh. Some suppliers offer time-of-use export rates paying more during peak demand periods.

Solar Panel Sizing Calculator — Domestic PV System Design

How We Calculate This

This calculator estimates the optimal solar PV system size for your property based on your annual electricity consumption and roof characteristics. It uses UK-specific solar irradiance data adjusted for orientation, pitch, and regional location.

Calculation methodology

Base irradiance: UK regional solar irradiance ranges from 900 kWh/kWp/year in Scotland to 1,100 kWh/kWp/year in southern England
Orientation factor: Adjusts output based on roof compass direction (south=100%, east/west=80%, north=55%)
Pitch factor: Optimal tilt is 30-40 degrees for UK latitude; steeper or flatter roofs lose some output
System sizing: Divides annual usage by effective irradiance to find the ideal system size in kWp

Financial returns

Savings come from two sources: avoiding grid electricity purchases (self-consumption) and income from exporting surplus to the grid under the Smart Export Guarantee. Self-consumed electricity saves at the full retail tariff rate, making higher self-consumption the key to better returns.