Dust and Staining

Following the research study conducted by a research team in Minya (Capital of the Minya Governorate in Upper Egypt) with relation to the degradation in solar transmittance of various tilted glass plates over the period of exposure to outdoor climate, it was found that an increase in dust accumulation contributed to air pollution, vehicular movements and wind would result in lower transmission of PV panels (Maghami, et al., 2016). We can conclude that solar irradiation received by the PV panels are largely affected by the accumulation of dust and stains, which eventually, lead to lower efficiency of the BIPV (Maghami, et al., 2016).

Figure 1. Degradation in Solar Transmittance of the Various Tilted Glass Plates Versus the Days of Exposure to Atmospheric Dust (Photo Credit: Maghami, et al., 2016)

As illustrated in Figure 1, it is observed that the efficiency of vertical PV panels is less likely to be affected by dust. The transmittance dust factor for 90° tilt angle caused a 3% decrease over the period of one month and thus, this indicated that the performance 90° tilt angle PV panels is not compromised by the external weather conditions – i.e. rain, wind and dust. On the other hand, if these same panels were to be integrated into the roof structures which has a tilt angle of 10-20°, the transmittance factor of the PV glass could reduce by up to 28%. This is rather a significant amount. Therefore, we can conclude that the efficiency of PV panel on vertical façade would not be as affected as compared to placing the panels on roofs and would produce the most efficient results.

The performance of the PV panels not only affected by the transmittance factor but also the type of deposition dust onto the surface. In this case, Figure 2 shows the cause of dust accumulation, type of dust as well as the factors causing dust to accumulate.

Figure 2. Cause of Dust Accumulation

Upon further research, Maghami and his team discovered that the transmittance reduction positively correlates to the dust deposition density as shown in Figure 3.

Figure 3. Observed Dust Deposition

According to research conducted in Poland, the efficiency of the PV panels decreased by 0.15% for every 0.1g/m² of dust deposition density (Klugmann-Radziemska, 2015). We conclude that the efficiency of the PV panels will decrease approximately 2% for vertically-installed PV, and approximately 10% for 20° tilted panel, for the dust accumulation over the one-month period. To add one, contamination by ash and pollution particles will lead to a doubled decrease in efficiency (Klugmann-Radziemska, 2015). Hence, we must take note of the potential decrease in efficiency of PV panels during the haze situation in Singapore as it is estimated to have 24% reduction in efficiency.

According to Building Maintenance and Strata Management Act 2004, high-rise buildings in Singapore are required to undergo cleaning process periodically twice a year. It is a standard requirement that forced building owners to maintain a clean building façade. Statistically, the dust accumulation on high-rise building can last up to 6 months in which would result in lower efficiency for the PV panels (if it is integrated into the vertical façade).

The dust intensity of different regions around the world is shown in Figure 4. The darker regions of the map indicate the higher level of dust. In the context of Singapore, we are in Zone 2 where the level of dust generated is around 30-44. This is relatively average as compared to other zones. Due to Singapore is located near the equator, we have a hot and humid climate, as well as abundant rainfall (National Climate Change Secretariat, 2016).

Figure 4. Dust Intensity Around the World

From the field study conducted by Maghami (2016), at least 20mm of rainfall is required to clean the surface of PV panel and therefore, Singapore is in a favourable position as we have an annual rate of 2331.2mm (Meteorological Service Singapore, 2016) – enough to clean regardless of hot or monsoon seasons.

However, despite the high rainfall, dust accumulation cannot be eradicated entirely as dust and stains may stick to the joints and corners of the PV panels. Furthermore, accumulation of dust at the corners of the PV panel can lead to a significant temperature increase of the panel itself. The temperature increase can rise up to a 10°C increase from its original surface temperature and thus, the efficiency of the solar cell decreases significantly (Pandian, Bansal, Thiruvadigal, & Sakthivel, 2016). If the panels are uncleaned for a long period of time, the accumulation of dust will lead to overheating of the PV panels, leading to long-term or permanent failure and requires to be replaced (Dorobantu, Popescu, Popescu, & Craciu, 2011).

Figure 5. P@rk Cafeteria

With reference to our case study on P@rk Cafeteria, stains from dust and dirt are visible in Figure 5. Not only it lowers the efficiency of the PV panels, it also degrades the aesthetic value of the cafeteria. As seen in Figure 6, the accumulation of dust and staining is seen in the joints of the structure.

Figure 6. Staining at Roof of P@rk Cafeteria