Air mass

Air mass (AM) is a relative measure of length in astronomy. It plays a role in energy generation through photovoltaics to calculate the efficiency of a photovoltaic system. It applies that the radiation power is highest in space and decreases as soon as the light penetrates the atmosphere (e.g. Earth's atmosphere). The same applies to the angle of incidence: if it is vertical, the output is highest. As the angle of incidence increases, the power decreases.
AM is calculated by dividing the path length of the light by the minimum length achieved with perpendicular irradiation. In space, the Air Mass is 0. For perpendicular irradiation on the Earth's surface, AM is 1. This value increases with the angle of inclination.