Solarrelative

Solarrelative is a proposed term used in solar energy and atmospheric science to describe a dimensionless index that expresses the relative intensity of solar radiation reaching a surface in comparison with a chosen reference value. The concept is not tied to a single, universally adopted definition, but it commonly appears in discussions of solar resource assessment and performance modeling as a normalized measure of irradiance.

Definition and variants

Solarrelative can be defined in several ways depending on the reference. A common formulation is the ratio of the actual irradiance on a surface, G, to a reference irradiance, G_ref, such as the extraterrestrial normal irradiance (theoretical maximum solar input outside Earth's atmosphere) or a modeled clear-sky irradiance for the same location and time. Thus solarrelative = G / G_ref. Variants may use different reference geometries (plane perpendicular to the sun, horizontal plane) or reference conditions (clear sky, standard atmosphere). When the reference is extraterrestrial, solarrelative values typically lie below 1, reflecting atmospheric attenuation; when the reference is a clear-sky model, values near 1 indicate good clearing conditions.

Calculation and data sources

Solarrelative can be computed from ground-based measurements (pyranometers, radiometers) or from satellite-derived irradiance estimates. It is often used in conjunction with other indices, such as solar angles, cloud cover, and aerosol optical depth, to characterize temporal variability and spatial patterns in solar resources. The calculation requires careful calibration and consistent reference choices to remain comparable across sites and studies.

Applications and limitations

Used in solar resource assessment, photovoltaic system design, performance forecasting, and climatological studies, solarrelative helps compare conditions over time or between locations. Its interpretation depends on the chosen reference, and results are sensitive to measurement quality, shading, and local atmospheric conditions.

See also

Solar irradiance, Clear-sky index, Photovoltaic performance, Solar resource mapping.