Total solar irradiance
Competence frameworks for the built environment – Core criteria for sustainability competence - Code of practice , Version 3, published by the Edge for the Construction Industry Council in February 2025, defines total solar irradiance (TSI) as: “The total amount of solar radiation in watts per square metre received outside the Earth’s atmosphere on a surface normal to the incident radiation and at the Earth’s mean distance from the Sun. Reliable measurements of solar radiation can only be made from space, and the precise record extends back only to 1978. Variations of a few tenths of a percent are common, usually associated with the passage of sunspots across the solar disk. The solar cycle variation of TSI is of the order of 0.1%.“
See also: Insolation.
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