Solindfald

Solindfald is a term used in Danish and Norwegian daylighting and solar energy contexts to describe the incidence of sunlight on a surface. It refers to the angle at which solar rays strike the surface, typically defined as the angle between the surface normal and the sun's rays. The solindfald influences the amount of direct solar irradiance received by the surface, as well as daylight quality and thermal gain. Factors include the surface orientation (tilt and azimuth), the sun’s position through the day and year (solar altitude and solar azimuth), and atmospheric conditions such as cloud cover and scattering.

In practical terms, solindfald is used to assess solar gains for buildings, shading design, and photovoltaic layouts. The direct component of irradiance on a tilted surface is affected by the cosine of the incidence angle, while diffuse and reflected components depend less directly on the solindfald. The concept is central to predicting daylighting performance, glare, and thermal behavior in built environments.

Calculation and modelling of solindfald rely on standard solar geometry. The incidence angle is determined from the sun’s position and the surface’s orientation, and is often computed with equations or simulated by energy modelling software. On-site measurements, using instruments such as pyranometers or sun photometers, can validate models or provide real-time data about solar incidence.

See also: solar geometry, solar altitude, solar azimuth, solar irradiance, daylighting.