Solar irradiation is the time-integral of irradiance: the total solar energy that arrives at a surface over a defined period. Annual plane-of-array irradiation at the panel tilt and orientation is the primary determinant of annual energy yield for a given system size. In the UK, south-facing tilted surfaces receive approximately 1,000 to 1,200 kWh/m²/year of total irradiation depending on location.
Solar irradiation data for UK sites is typically sourced from PVGIS (JRC Photovoltaic Geographical Information System), Meteonorm, or site-measured data where available. Energy yield modelling tools use hourly irradiation data alongside module and inverter specifications to predict annual generation, informing PPA pricing, ROI calculations, and project finance models.