Influence of Varying Wind Speeds, Installation Heights, Orientation and Tilt Angles on Solar PV Modules and Design of Automated PV Surface Cleaning System

Abstract

Solar photovoltaic (PV) is one of the emerging technologies widely acknowledged as a potential solution to energy poverty. This is because of its high reliability, long life, and automatic operation with minimal maintenance requirements, despite its low conversion efficiency and high capital costs. Studies have been conducted on mechanisms of improving the power conversion efficiencies (η) of field deployed PV modules which tend to degrade with time. For instance, dust, dust accumulation, shadowing, birds dropping, water droplets, and wind speeds have been independently investigated. Much focus is laid on the effect of dust accumulation, with little attention on correlation between wind speeds, relative humidity and module orientation on dust deposition rates and characteristics, on PV modules which form the basis of soiling. This study looked at how wind profiles, relative humidity, and module placement affected dust deposition on the surfaces of photovoltaic modules, and thus their overall performance in an outdoor setup. The analysis of dust deposits on five photovoltaic (PV) systems installed at five study sites within Machakos County was done. The selection of the study sites was informed by the environmental conditions, location, topography and the soil types. The effect of module installation height, tilt angle, and orientation on the rate of dust deposition on the surfaces of PV modules was investigated. As a result, the effect of various dust categories on Pmax and η was quantified. During the study, the rate of dust deposition was noted and the elemental concentration of the dust deposits identified and used to classify the dust into biogenic, geogenic and anthropogenic origin. Effect of the dust deposits on the performance of mono-crystalline silicon (m-Si) solar modules exposed to ambient conditions was investigated. Correlation between adhesive forces of the dust deposits to the resuspension forces required to naturally dislodge the adhered dust particles on PV surfaces was probed. Thereafter, an automated scalable PV module cleaning system utilizing air and water jets fitted in a bi-directional motor was fabricated and tested on a dusty module. Solar PV modules installed at the five study sites showed a monthly average decrease in η of 2.60%, 3.48%, 8.1%, 5.5%, and 2.76% at sites 1, 2, 3, 4 and 5, respectively. Similarly, leeward-facing module surfaces exhibited higher deposition rates as compared to the windward facing modules in southerly winds. In addition, sites with traces of anthropogenic particles on dust samples collected from PV surfaces show a greater decrease in efficiency, while sites with biogenic and geogenic particles show minimal effects. An abundance of anthropogenic dust particles, combined with a mild tilt and leeward orientation, resulted in a faster degradation rate of maximum power and efficiency. Similarly, the monthly modules peak power (Pmax) degradation rate was observed to be higher (8.8%) for sites experiencing a higher temperature coefficient (Tc) for VMPP due to temperature effects of soiling, lower wind speeds, and a higher relative humidity. Lower deposition rates were observed in locations with higher wind speeds and a higher module tilt angle, resulting in a lower effect on the reduction of current and voltage parameters. Similarly, the average wind speeds at each site were insufficient for complete particulate resuspension of small particles (less than 500 µm) adhering to the PV module surface. As a result, dust accumulations on the surface of PV modules had a significant negative impact on current and voltage xvii parameters. Therefore, an automated self-cleaning system was designed, fabricated and tested based on the study findings to counter-act the effects of soiling observed on the PV modules. The study findings revealed a 12.26% increase in η of the dusty solar PV module after cleaning using the automated system as compared to its performance before exposure to dust. From the study findings and existing challenge of inability to incorporate self-cleaning mechanism at the design stage of solar PV modules, we recommend incorporation of the automated self-cleaning model in the design of PV module frames. This is contrary to the existence of the automated self cleaning system as a separate entity incorporated at the installation stage. This remedy provides a tailor-made solution to soiling hence averting the deleterious effects of soiling on PV modules