globaalisäteily

Globaalisäteily, known in English as global solar radiation or global horizontal irradiance (GHI), is the total amount of short‑wave solar energy received per unit area on a horizontal surface. It is measured in watts per square metre (W/m²) and represents the sum of direct beam radiation from the sun and diffuse radiation scattered by the Earth's atmosphere. GHI is a key parameter in solar energy forecasting, climatology, and agricultural planning, as it directly influences the performance of photovoltaic systems, solar thermal collectors, and the natural light environment for plants.

The measurement of globaalisäteily is typically carried out using pyranometers, instruments that capture solar irradiance over a 180‑degree view of the sky. Data from pyranometers are integrated over time to produce hourly, daily, or monthly averages, which are then used in building climate databases and informing renewable‑energy models. Advanced satellite‑based algorithms now complement ground measurements, providing global coverage and temporal resolution that enable large‑scale assessment of solar resource potential.

Globaalisäteily varies with geographic location, altitude, cloud cover, atmospheric composition, and the angle of the sun in the sky. At the equator during clear‑sky conditions, GHI can exceed 1,000 W/m², whereas polar regions may see values near zero during winter months. Air pollution and aerosol loading can reduce GHI by scattering and absorption, whereas dust‑laden environments may occasionally increase diffuse components.

Applications of globaalisäteily extend beyond power generation. It is used to calibrate climate models, assess risk from solar ultraviolet exposure in public health, and inform the design of daylighting systems in architecture. Continued improvements in measurement technology and data assimilation are enhancing the accuracy of GHI predictions, thereby supporting the expansion of solar energy infrastructure worldwide.