Soiling, cleaning frequency, and oversizing of pole-mounted photovoltaic configurations in arid climates

This paper presents an experimental assessment of soiling effects, cleaning requirements, and design implications for pole-integrated off-grid photovoltaic systems in arid environments, with emphasis on low-maintainability installations, where cleaning is impractical and soiling is a major concern. This study is based on a one-year field measurement campaign at the Qatar Environment and Energy Research Institute's Outdoor Test Facility in Doha, Qatar. Five photovoltaic configurations are evaluated simultaneously under identical conditions: 22°-tilted back-contact, 22°-tilted bifacial, vertical back-contact, vertical bifacial, and octagonal Vertical Photovoltaic Tube modules. The key metrics are the effective soiling loss, the threshold-based cleaning frequency, and the capacity oversizing factor that compensates soiling when cleaning is not possible. Since optical sensor-based instrumental soiling data exists only for the tilted reference plane, image-based scaling factors are applied to estimate the soiling in the other configurations. The results show a geometry-dependent soiling hierarchy. Tilted configurations require approximately 19 threshold-triggered cleanings per year; if they are never cleaned, they need 1.7% (best month) to 66.4% (worst month, reconstructed) additional capacity, and 14.2% under typical (campaign-mean) conditions. Vertical configurations require one to two cleanings per year and 0.3–6.4% additional capacity. The Vertical Photovoltaic Tube triggered no cleaning in the observed year and has an estimated 0.1–2.0% additional capacity (soiling estimated from image-based factors). These findings indicate that soiling resilience is a principal design advantage of the Vertical Photovoltaic Tube for remote, low-maintenance deployments, and they provide design guidance on module geometry, cleaning strategy, and system sizing in hot-arid climates.