oa Performance of Antisoiling Coatings for Enhancement of PV Panel Performance in Doha

Severe temperature, humidity and dust characteristic of the desert region are major challenges in power generation efficiency of photovoltaic (PV) systems in the gulf region. Soiling can lead to daily average energy loss of up to 4% [1], necessitating frequent cleaning which adds to the cost. One of the solutions to the problem is to use anti-soil coatings, where hydrophilic or hydrophobic coatings with spectral characteristics suitable for PV applications are added to the outer layer of PV glass. However, it has been shown that the effectiveness of the coatings in reducing accumulation of dust in PV panels is dependent on climatic conditions [2-4]. Since coatings add to the cost of solar panels, it is imperative that the coatings are tested for suitability at the intended location or similar weather conditions prior to large scale application. In this work, anti-soil coatings on PV glass were tested outdoor in order to assess the effectiveness of the coatings as remedy for PV performance degradation upon exposure to environmental conditions of the Gulf region. Industrial anti-dust coatings on solar glass and uncoated solar glass; sample size ∼2.5 cm ×  2.5 cm, were tested outdoor at Qatar Foundation's solar test facility (STF) in Doha. The coatings were hydrophobic (contact angle pre-exposure 83-90 degrees), while uncoated samples were hydrophilic (contact angle pre-exposure 34 -47 degrees). Measurements were taken pre-exposure (as received) and periodically upon exposure. The measurements were repeated after cleaning, which includes 3 day rain (Rain Clean), wash with free-running deionized (DI) water (DI-Clean), and wash with DI water with scrubbing (DI+S). The main test parameter of interest was radiant energy transmission properties. The impact of wind and humidity on energy transmission and the morphology and composition of the dust particles on samples were also analyzed. The following is a summary of the findings. Performance degradation due to dust is very high. Energy transmission loss of up to 37% was recorded during 13 weeks (week 8-week 20) of exposure, without dust storms (Fig. 1, 2).The advantage of coatings (over uncoated samples) is only marginal. Example, the average periodic energy transmission during week 8 –week 20 is < 1.5% higher for coated samples. Therefore, the tested anti-soil coatings seem not to offer significant remedy to performance degradation due to dust in Qatar. Patterned glass has better transmittance than plain glass, irrespective of coating type. Example, the average periodic energy transmission during week 8 –week 20 of exposure is ∼6% higher for patterned glass. The highest impact of dust in energy transmission is in the wave length range below 500 nm. This appears to be due to the high concentration of small (submicron) dust particles (see SEM images in Fig. 3).Cleaning recovers transmission to pre-exposure levels, except for shorter wavelengths (below 500 nm). This may suggest that smaller dust particles are difficult to remove. In-addition, presence of surface contaminants (non-dust-related) may require aggressive cleaning to remove.Dry wind appears to give a cleaning effect. Example, during W10 –W11, (Fig. 1) a period of fast winds (>2.5 m/s) and low humidity ( < 27%), energy transmission improved (instead of decreasing or remaining un-changed) for most of the samples. The morphology (Fig. 3) and compositions of dust on samples (Fig. 4) appear to be the constituents of the desert dust [5, 6]. However, dust particles exceptionally rich in Carbon (>30%), Iron (2%), Aluminium (>;4%) and Sulfur (>5%) have been observed. These may suggest existence of contribution from environmental activities such as transport and construction [7]. Dust particles with elevated amounts of Chlorine (3%) and Sodium (4%) have also been observed. These may indicate a contribution of salts from the sea [6, 7]. References [1] S. Semaoui, A. H. Arab, E. K. Boudjelthia, S. Bacha, and H. Zeraia, «Dust Effect on Optical Transmittance of Photovoltaic Module Glazing in a Desert Region,» Energy Procedia, vol. 74, pp. 1347-1357, 8// 2015. [2] Z. Abrams, P. Gonsalves, B. Brophy, and J. Posbic, «Field and Lab Verification of Hydrophobic Anti-Reflective and Anti-Soiling Coatings on Photovoltaic Glass,» Proceedings of the 29th EUPVSEC, pp. 2759-2764, 2014. [3] E. Klimm, T. Lorenz, and K. Weiss, «Can anti-soiling coating on solar glass influence the degree of performance loss over time of PV modules drastically?,» the 28th EUPVSEC, 2011. [4] E. Klimm, L. Ost, B. Spiegelhalter, and K. A. Weiss, «Tests of functional coatings on glass adapted to extreme - arid and maritime - climatic conditions for solar energy systems,» in Photovoltaic Specialist Conference (PVSC), 2015 IEEE 42nd, 2015, pp. 1-5. [5] T. Sarver, A. Al-Qaraghuli, and L. L. Kazmerski, «A comprehensive review of the impact of dust on the use of solar energy: History, investigations, results, literature, and mitigation approaches,» Renewable and Sustainable Energy Reviews, vol. 22, pp. 698-733, 6// 2013. [6] B. S. Yilbas, H. Ali, M. M. Khaled, N. Al-Aqeeli, N. Abu-Dheir, and K. K. Varanasi, «Influence of dust and mud on the optical, chemical, and mechanical properties of a pv protective glass,» Scientific Reports, vol. 5, p. 15833, 10/30/online 2015. [7] H. K. Elminir, A. E. Ghitas, R. H. Hamid, F. El-Hussainy, M. M. Beheary, and K. M. Abdel-Moneim, «Effect of dust on the transparent cover of solar collectors,» Energy Conversion and Management, vol. 47, pp. 3192-3203, 11// 2006.