Measurement and modeling of diffuse irradiance masking on tilted planes for solar engineering applications

Photovoltaic and solar thermal projects require accurate solar irradiance data and models for the design, assessment, and forecasting of power output. For panels and solar collectors installed in arrays, the view toward the sky and ground is restricted by the surrounding rows. This paper analyzes the impact of view obstructions on the diffuse irradiance distribution in fixed-tilt arrays, addressing the insufficient research coverage to date.

Irradiance was measured using high-precision pyranometers placed at ten positions throughout an experimental solar collector array for 3.5 and 6 m row spacings and 30º , 37.5º , and 45º tilt angles (relative row spacings between 0.68 and 1.51). A novel anisotropic transposition model was developed to calculate the diffuse tilted irradiance along the collector height, accounting for diffuse irradiance masking due to view obstructions.

The model was also solved inversely, obtaining local global horizontal irradiance from global tilted irradiance. The validation showed that the model accurately captures the distinct shape of the diffuse irradiance distribution. Results indicate a strong effect of view obstructions for narrow row spacings and steep tilt angles.

For the most extreme configuration (3.5 m row spacing, 45º tilt angle, 1.67 relative row spacing), the diffuse irradiance was reduced to 64% at the bottom and 89% on average, relative to the top of the collector. As a consequence, measurements at the top can result in biased performance assessments.