Abstract
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 30°, 37.5°, and 45° 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, 45° 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.
Highlights
A major task in solar energy projects is the measurement and modeling of the incident solar irradiance on the collecting surfaces
For the most extreme configuration (3.5 m row spacing, 45◦ 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
For the wider row spacings (CC #4-6), the model performances are similar, as view obstructions only have a minor effect and the average global tilted irradiance is nearly uniform along the collector height
Summary
A major task in solar energy projects is the measurement and modeling of the incident solar irradiance on the collecting surfaces. The total diffuse irradiance is calculated as the sum of a background isotropic component and one or two anisotropic components representing the circumsolar region and/or horizon band These models are all designed for unobstructed tilted surfaces and only few studies are available for diffuse irradiance masking of collector arrays. The most elaborate approach for collector arrays is by Varga and Mayer (2021), which propose a modified version of the Hay transposition model Their model considers the impact of view obstructions of the front collector row separately for the isotropic and circumsolar diffuse irradiance part. A modified version of the anisotropic Hay-andDavies transposition model is developed which considers view obstructions in fixed-tilt collector arrays. This model is applied in the inverse direction. This section describes the original Hay transposition model, its limitations for collector arrays, and the novel transposition model
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