Diffuse Radiation

In photovoltaics, diffuse radiation refers to the portion of sunlight that does not directly reach a surface but is scattered in the atmosphere first. This scattering occurs due to interactions with air molecules, water droplets (clouds), and other particles. Unlike direct radiation, which reaches the Earth as a parallel beam of energy, diffuse radiation is irregularly distributed and comes from all directions in the sky.

Formation and Influencing Factors:

  • Scattering: The main cause of diffuse radiation is Rayleigh scattering by air molecules. It is particularly strong at shorter wavelengths (blue light) and gives the sky its blue color.
  • Clouds: Clouds reflect and scatter a large portion of sunlight. The denser the cloud cover, the greater the proportion of diffuse radiation.
  • Aerosols: Dust, soot, and other particles in the atmosphere can also contribute to scattering.
  • Season and Time of Day: The amount of diffuse radiation varies depending on the season and time of day. In winter and under overcast skies, diffuse radiation predominates, while in summer with clear skies, direct radiation is dominant.

Importance for Photovoltaics:

  • Impact on Yield: Diffuse radiation significantly contributes to the total yield of a photovoltaic system. It is especially important under overcast skies or in regions with high air pollution where the proportion of diffuse radiation is high.
  • Orientation and Inclination: Unlike direct radiation, which is highly dependent on the orientation and tilt of solar modules, diffuse radiation is less direction-sensitive.
  • Module Characteristics: Modern solar modules are capable of converting both direct and diffuse radiation.

Measurement and Calculation:

Diffuse radiation is measured using pyranometers, which capture all radiation reaching a horizontal surface. Pyrheliometers, on the other hand, only measure direct radiation. To calculate diffuse radiation, direct radiation is subtracted from the global radiation (the total of direct and diffuse radiation).

Summary:

Diffuse radiation is a crucial factor for the performance of photovoltaic systems. It ensures that solar modules can generate electricity even under cloudy skies or during morning and evening hours. To optimize the yield of a photovoltaic system, it is important to consider both direct and diffuse radiation.

Additional Keywords: Global Radiation, Direct Radiation, Rayleigh Scattering, Solar Module, Photovoltaic Yield