Solar / Global Radiation

Solar radiation, or global radiation, is the total shortwave energy arriving from the sun on a horizontal surface, measured in watts per square meter (W/m²). It is the sum of two parts: the direct beam coming straight from the sun's disc, and the diffuse radiation scattered across the whole sky by cloud, air, and aerosols. Reported as global horizontal irradiance, it rises and falls through the day with the sun's angle and is cut by cloud, haze, and shading. It covers the shortwave band (ultraviolet, visible, and near-infrared) that carries the sun's energy to the ground, and it is distinct from the narrower band of photosynthetically active radiation that plants use.

Solar radiation is the primary energy input to the surface, driving temperature, evaporation, plant growth, and power generation alike, which makes it a cornerstone measurement in energy, agriculture, and meteorology.

For solar-energy projects, irradiance is the fuel: it determines how much a photovoltaic array or thermal collector can produce, so measured radiation underpins yield prediction, performance monitoring, and the detection of soiling or faults. In agriculture it drives photosynthesis and, together with temperature and humidity, the evapotranspiration that governs crop water demand and irrigation scheduling. In meteorology and building science it feeds energy-balance and climate models and informs the design of shading, daylighting, and cooling loads.

Across all of these, solar radiation is a supplied energy that everything else responds to, so measuring it accurately turns qualitative expectations about sun and cloud into quantitative inputs for design and control.

Global radiation is measured with a pyranometer, a sensor with a horizontal, upward-facing element under one or two glass domes that admit the full shortwave band while excluding longwave heat. Two technologies dominate: thermopile pyranometers, which sense the heat absorbed by a black surface and offer a flat spectral response classified under ISO 9060; and silicon-photodiode sensors, which are lower cost but respond over a narrower band. As a professional meteorological sensor rather than a built-in reading, a pyranometer is connected to a Thiamis gateway for continuous irradiance logging, and its glass dome must be kept clean and free of dew, frost, and dust to stay accurate.