Solar radiation spectrum - What type of radiation does the sun produce. The sunlight that we know has its origin in the nuclear fusion process that takes place in the interior of the sun. The sun is 'fired' by this process to an active surface temperature of around 5500 ° C and emits radiation as a result of this temperature, the sunlight.
If we disassemble the sunshine with a prism (think of a rainbow), we see that the sunlight consists of a large number of colours. To be precise, we see high-energy (a short wavelength) purple up to low energy (a long wavelength) red. About 45% of the light emitted by the sun consists of the visible light that we can perceive with our eyes.
The sun behaves broadly like a black beam. This means that the distribution of the emitted light is almost purely dependent on the temperature of the sun, according to the laws of Planck and Wien. It is through this assumption that we can estimate the temperature of the sun surface at about 5500 ° C using the spectrum. Points on which the sun deviates are the so-called 'absorption lines'. Places where the sunlight shows holes in the colour range due to absorption by specific components.
What also stands out is the fact that the sunlight that reaches us (the red part of the graph) looks very different again. This has to do with the atmosphere of the Earth. In our atmosphere, there are all kinds of gases, each of which absorbs a specific part of the sunlight. Consider, for example, ozone, which absorbs ultraviolet light and water vapour, which is responsible for the filtering of about 70% of the infrared. Water is not blue in large quantities for nothing, the red light is more absorbed! Without this protective effect of our atmosphere, we would quickly fall prey to the carcinogenic ultraviolet radiation.
As can be read in the article on photovoltaic cells, specific semiconductors have a material-specific band gap. If the semiconductor sunlight is applied with just the right energy (understand: wavelength), an electron can jump from the valence to the conduction band. However, the power of the sunlight must meet the requirement set by the material. If the energy is too high, the radiation is reflected or converted into heat. If the power is too low, the radiation is transmitted or converted into heat.
It is for this reason that a PV panel becomes warm when it is put in the sun. Sunlight that is not used is partially converted into heat. The blue colour is at this moment also explained. Because the bandgap of the commonly used silicon corresponds to the red and green part of the visible light, the blue light is dismissed as too energetic.
Back to the main article