Solar rays can be distinguished according to their wavelengths, which determine visible light, infrared and ultraviolet radiation.
Visible light constitutes about 40% of the radiated energy, infrared 50% and ultraviolet the remaining 10%.
Most of the infrareds are “near infrared” or “short-wave infrared” rays, with wavelengths shorter than 3 000 nanometres, so they are not considered “thermal radiation”.
The sun’s primary benefit for most people is light, the use of which can be improved in buildings to reduce energy consumption.
This area of development, called day lighting, is one of the avenues to reducing energy consumption in buildings.
Solar irradiative energy is easily transformed into heat through absorption by gaseous, liquid or solid materials.
Heat can then be used for comfort, in sanitary water heating or pool water heating, for evaporating water and drying things (notably crops and food), and in space heating, which is a major driver of energy consumption.
Heat can also be transformed into mechanical work or electricity, and it can run or facilitate chemical or physical transformations and thus industrial processes or the manufacture of various energy vectors or fuels, notably hydrogen.
However, solar radiation can also be viewed as a flux of electromagnetic particles or photons.
Photons from the sun are highly energetic, and can promote photoreactions such as in photosynthesis and generate conduction of electrons in semiconductors, enabling the photovoltaic conversion of sunlight into electricity.
Other photoreactions are also being used, for example photocatalytic water detoxification.
Note that there are many reasons for capturing solar and deploying solar energy while fossil fuels still dominate the global economy’s energy balance.
Thus, from the two basic ways of capturing the sun’s energy, apart from day lighting, i.e. heat and photo-reaction, we distinguish four main domains of applications: photovoltaic electricity, heating (and cooling), solar thermal electricity, and solar fuel manufacture.