Among the various methods of measuring diffuse solar irradiance, shadowing devices are ones of the
most commonly used in solar research all over the world. These instruments work with a basic pyranometer,
properly calibrated for the measurement of solar irradiance, with a shadowing element, which
can be a disk or a band (Drummond’s shadow-band), that prevents the direct incidence of solar beam
irradiance on the sensor. This method is capable of precise measurements, but sensor outputs have to
be corrected, so as to quantify the amount of diffuse irradiance that the band blocks from reaching the
sensor. Several authors have advanced different expressions for this correction factor, most of which only
apply to horizontal and equator-oriented tilting pyranometers. In this work, we present a general
approach to calculate the geometrical correction factor for a tilted sensor, oriented towards all possible
azimuth and zenith angles, which permits the measurement of solar diffuse irradiance on any tilted and
oriented surfaces. Furthermore, five total correction models are adapted for measurement in any given
direction and evaluated on vertical walls pointing the four cardinal directions. Our results show that geometrical
correction improves the Mean Bias Difference (MBD), the Root Mean Squared Difference (RMSD)
and the l0:99 statistics by 60%, 62% and 56%, respectively, in contrast with the raw data. The LeBaron et al.
model gives the most accurate figure for total correction according to MBD, RMSD and l0:99 statistics,
with promising average performances of 97%, 91%, and 96%, respectively
