air mass (AM)
Inphotovoltaics, solar radiation is affected by the azimuth of the sun. The more obliquely the sunlight falls, the more atmosphere it must pass through, which attenuates it. The air mass is called Air Mass( AM).
In photovoltaics, the Air Mass is a dimensionless value that results from the angle of incidence at our latitudes to the perpendicular incidence at the equator. At perpendicular irradiation at the equator, the Air Mass is 1. At our latitudes, the value for the Air Mass changes with the seasons.
In summer, the angle of inc idence for sunlight is up to 60°, which corresponds to an Air Mass of 1.15. At an angle of incidence of 41.8°, the Air Mass is 1.5. In winter, the angle of incidence is very shallow and is up to 15°. The Air Mass is then 14. The Air Mass is then 14. The light must pass through an atmosphere 14 times thicker than with an Air Mass of 1.