Sensors should be calibrated regularly.Measurements should be performed at least every hour.Only high quality measurement sensors should be used.But to be useful, these measurements should fulfill a number of conditions: There is little doubt that the very best way to measure solar radiation is to use high-quality sensors on the ground. 1.1 Estimating the solar radiation intensity The data provided by PVGIS contains both irradiance and irradiation values. While irradiation is the amount of solar energy received per unit area during a period of time, therefore energy and it is expressed in Wh/m 2. Irradiance is the solar power falling into a surface per unit area and unit time. Concepts like irradiance and irradiation should be clarified. Through the pages of PVGIS web, we talk about solar radiation and use it in a generic way but we also use other terms that should be explained. This value is normally modelled and is used as input data for other models applied for the estimation of the solar radiation at normal atmospheric conditions. Solar radiation under clear sky conditions (without clouds) and clean and dry atmosphere is a very important parameter as it provides information about the maximum radiation available at any location. The beam component is only available when the solar disc is not blocked by clouds, while the diffuse component is always available, being the only radiation available whenever clouds block the solar disc. The third component, not always taken into account, is the reflected radiation from the ground surface or nearby obstacles. The second part or diffuse is the solar radiation that reaches the ground after being reflected or scattered by the atmosphere and is considered to arrive from the whole sky dome. The first one, named beam or direct radiation, is the fraction of the solar radiation that reaches the ground without being attenuated by the atmosphere and can be modelled as coming directly from the solar disc. The solar radiation received at ground level, known as global radiation is sum of three components. Not only the broadband value is different, but also these processes of absorption and attenuation affect differently the wavelengths of solar radiation, so the spectral distribution of the solar radiation at ground level differs from the extraterrestrial one. ![]() However, the main source of attenuation is the cloud cover. These are due to the atmosphere components, such as ozone or CO 2, and solid and liquid particles in suspension like aerosols or water vapour. ![]() The solar radiation that reaches the top of the atmosphere on a perpendicular plane to the rays, known as solar constant, has an average value of 1361-1362 W/m 2 which varies somewhat depending on the position of the Earth in its elliptical orbit.Īs the solar radiation goes through the atmosphere it suffers different processes of absorption, dispersion or scattering that result in lower levels of solar radiation being received at the Earth's surface.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |