10 Module Deployment and Energy Rating
257
(a)
(b)
Fig. 10.5 a Spectral response (as external quantum efficiency, EQE, in electrons per incident
photon) of c-Si and CdTe modules, and of a pyranometer, compared with the AM1.5 spectrum;
b Comparison between AM1.5 spectral irradiance and real, field measurements. Measured spectra
have been recorded at zero tilt in Gonghe, China (latitude φ = 36 ◦ 17 N, horizontal irradiance,
fixed installation), on the 2nd May 2018 at 9:30 in the morning and at solar noon
• and the spectral irradiance measured again in Gonghe at zero tilt, but at solar
noon.
Both spectra were recorded in clear-sky conditions and at zero tilt, but not surprisingly, the measurement in the morning shows a larger difference from the AM1.5
spectrum, both in terms of absolute values and shape of the spectrum. The reason
is the wider angle of incidence in the morning (hence, a lower irradiance due to the
cosine effect) and a higher diffuse component than the direct one (hence a larger blue
content in the spectral irradiance).