Air Mass (solar Energy) - Cases

Cases

• AM0

The spectrum outside the atmosphere, the 5,800 K black body, is referred to as "AM0", meaning "zero atmospheres". Solar cells used for space power applications, like those on communications satellites are generally characterized using AM0.

• AM1

The spectrum after travelling through the atmosphere to sea level with the sun directly overhead is referred to, by definition, as "AM1". This means "one atmosphere". AM1 (=0°) to AM1.1 (=25°) is a useful range for estimating performance of solar cells in equatorial and tropical regions.

• AM1.5

Solar panels do not generally operate under exactly one atmosphere's thickness: if the sun is at an angle to the Earth's surface the effective thickness will be greater. Many of the world's major population centres, and hence solar installations and industry, across Europe, China, Japan, the United States of America and elsewhere (including northern India, southern Africa and Australia) lie in temperate latitudes. An AM number representing the spectrum at mid-latitudes is therefore much more common.

"AM1.5", 1.5 atmosphere thickness, corresponds to a solar zenith angle of =48.2°. While the summertime AM number for mid-latitudes during the middle parts of the day is less than 1.5, higher figures apply in the morning and evening and at other times of the year. Therefore AM1.5 is useful to represent the overall yearly average for mid-latitudes. Consequently, the solar industry uses AM1.5 for all standardized testing of terrestrial solar panels.

• AM2~3

AM2 (=60°) to AM3 (=70°) is a useful range for estimating the overall average performance of solar cells installed at high latitudes such as in northern Europe. Similarly AM2 to AM3 is useful to estimate wintertime performance in temperate latitudes, e.g. airmass coefficient is greater than 2 at all hours of the day in winter at latitudes as low as 37°.

• AM38

AM38 is generally regarded as being the airmass in the horizontal direction (=90°) at sea level. However, in practice there is a high degree of variability in the solar intensity received at angles close to the horizon as described in the next section Solar intensity.

• At higher altitudes

Airmass coefficient reduces with increasing altitude above sea level. Therefore solar panels installed at high altitudes, e.g. in an Altiplano region, would use lower AM numbers than for the corresponding latitude at sea level: AM numbers less than 1 towards the equator, and correspondingly lower numbers than listed above for other latitudes.