Solar irradiance

Solar irradiance is the Sun’s radiant power received per unit area, measured in watts per square metre. Its value depends on location, orientation, distance, and atmospheric conditions.

Solar constant: The mean solar irradiance at Earth’s average distance from the Sun, measured on a surface perpendicular to incoming sunlight outside the atmosphere. It gives the reference value for solar irradiance at the top of Earth’s atmosphere.
Radiant flux: The rate at which electromagnetic radiation carries energy, measured in watts. Irradiance is radiant flux received per unit area.
Photovoltaics: The conversion of light into electrical energy using semiconductor materials. Incident solar irradiance sets the available light input for photovoltaic power generation.
Total solar irradiance: The solar radiant power received per unit area at Earth’s mean orbital distance, integrated across wavelengths outside the atmosphere. It tracks the Sun’s total energy input before atmospheric filtering.
Inverse-square law: A physical law stating that a point source’s intensity decreases in proportion to the square of distance. It explains how solar irradiance changes as the distance from the Sun changes.
Radiant exposure: The radiant energy received per unit area over a specified time, measured in joules per square metre. It is irradiance accumulated over time, rather than an instantaneous power density.
Solar thermal energy: The use of sunlight to produce heat for practical or electrical applications. Solar irradiance determines the heat a collector can capture.
Solar spectral irradiance: The Sun’s irradiance at Earth distributed across wavelength or frequency outside or within the atmosphere. Its spectrum shows how solar power is apportioned across wavelengths.
Atmospheric extinction: The reduction of radiation passing through an atmosphere by absorption and scattering. It accounts for sunlight lost between the top of the atmosphere and the ground.
Radiance: Radiant power emitted, reflected, transmitted, or received in a specified direction per unit projected area and solid angle. Unlike irradiance, radiance retains information about the direction of incoming light.

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