Diffuse radiation is the scattered form of sunlight from the Sun, which does not have a single directional source. This radiation is scattered by particles in the atmosphere (such as dust grains, water droplets, or molecules) before reaching the Earth's surface or solar panels.
What is diffuse radiation?
Features:
- Diffuse radiation comes from all directions and not directly from the Sun.
- It is responsible for the "diffuse" illumination of the sky, which means light that is visible even in cloudy weather or in shady places, for example.
Sources:
- Atmosphere: The scattering of sunlight by particles in the atmosphere.
- Reflections: Sunlight reflected from the ground, buildings, or other objects.
Diffuse radiation and solar systems
Diffuse radiation is particularly important for solar systems, as solar panels can utilize not only direct solar radiation, but also diffuse radiation.
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Energy production in cloudy weather:
On cloudy days, when direct radiation decreases, diffuse radiation ensures that solar systems continue to produce energy.
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Local factors:
In shady locations, such as densely built-up urban environments, diffuse radiation plays a significant role in the energy production of solar cells.
- Efficiency: Solar cells that utilize diffuse radiation, such as panels made with thin-film technology, are particularly efficient in diffuse light.
What affects diffuse radiation?
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Cloud cover:
The greater the cloud cover, the more light is scattered in the atmosphere, increasing the ratio of diffuse radiation to direct radiation.
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Air pollution:
Pollutant particles in the air (such as dust, smoke) increase the degree of scattering, and thus the amount of diffuse radiation.
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Humidity:
At high humidity, water particles scatter light, which increases the intensity of diffuse radiation.
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Sun angle: During lower sun positions (e.g. morning or late afternoon), light travels a longer path through the atmosphere, resulting in more scattering.
- Latitude: The proportion of diffuse radiation compared to direct radiation may be greater at higher latitudes, where sunlight is more likely to be scattered by atmospheric conditions.
Comparison of diffuse and direct radiation
| Property | Diffuse radiation | Direct radiation |
|---|---|---|
| Source | Diffused light | Light coming directly from the Sun |
| Direction | From all directions | From one direction |
| Significance for solar panels | Important in cloudy or shady weather | Dominant in clear weather |
| Dependence on sunlight | Depends less | It strongly depends on the intensity of sunlight |
Summary
Diffuse radiation plays a significant role in the performance of solar PV systems, especially in cloudy or shady conditions. Although direct radiation is more dominant on clear days, diffuse radiation ensures that solar panels can produce energy under varying conditions. By considering local environmental factors and selecting appropriate technologies, diffuse radiation can be effectively utilized in the design and operation of solar PV systems.