As conventional energy sources decrease and worldwide power demand grows, the appeal of photovoltaic (PV) systems as sustainable and ecofriendly energy sources has grown. PV system installation is influenced by geographical location, orientation, and inclination angle. Dust is a collection of tiny particles composed of microscopic solid inorganic and organic particles such as soil particles, ash (including pollutants from factories, vehicles, and firewood), bacteria, and so on, that has a diameter smaller than that of the air 500–1000 µm. These particles vary in size, volume, chemical concentration, and shape. Dust properties, such as size, shape, chemical composition, transmittance, absorption, reflection, thermal conductivity, and emissivity, can all affect the thermal and electrical behavior of PV systems. It is essential to consider that dust properties can vary depending on the location and environmental conditions.
1. Dust Light Absorption
Absorption is the ability of dust particles to absorb light. Dust particles that can absorb light can reduce the light that arrives at the PV cells, lowering the PV system’s efficiency
[1][2]. Dust can absorb heat and sunlight, raising the PV module’s temperature
[3]. This can cause thermal stress on the PV cells, leading to decreased performance and potential damage over time. The amount and chemical composition of dust can significantly impact dust light absorption properties
[4]. Dust composed of large particles and/or with a high absorption coefficient has a higher absorption rate than those with small particles and/or absorption coefficients
[2].
Various parameters, including dust particle diameter, morphology, and elemental composition, can influence dust light absorption on PV
[5]. For example, dust particles that are smaller in size are more likely to scatter light and have lower absorption rates, while larger particles are more likely to absorb and reflect light. A study by
[5] used a spectrum optical absorption measurement device to measure the absorption coefficients in the wavelength’s spectrum from 300 to 800 nm with an accuracy of 50 nm. For particle sizes greater than 0.5 m, the dust light absorption coefficient was shown to be associated with particle number concentration, although the correlation was weaker for smaller particles. Similarly, dust particles with irregular shapes are more likely to scatter light and have lower absorption rates than regular shapes
[1]. Limestone, carbon-based soot, and red soil with oxidized iron are three common air contaminants with elevated light-absorption coefficients
[2].
The chemical composition of dust particles can also affect their absorption rate, with metallic particles having a higher absorption rate than nonmetallic particles
[1]. In general, dust composed of large particles and/or has a high absorption coefficient has a higher absorption rate than dust consisting of small particles and/or has a low absorption coefficient. This is why dust composed mainly of iron oxide (Fe
2O
3) has a higher absorption rate compared to dust composed mainly of silica (SiO
2)
[6]. To summarize, understanding the impact of dust amount and chemical composition on the dust light absorption property is essential for investigating the impact of dust on PV performance and thermal behavior.
2. Dust Transmittance
The dust accumulation on the PV cell considerably impacts the incident solar light transmittance
[7]. The transmittance of dust on PV is the ability of dust particles to allow light to pass through them. Low transmittance of dust particles can decrease the amount of light that arrives at the PV modules and reduces the efficiency of the PV system
[8]. The amount and chemical composition of dust can alter how well light passes through the dust layer. The amount of dust on a surface can affect the transmittance by decreasing it as the dust layer becomes thicker
[9]. This is because more dust particles scatter and absorb the light, reducing the amount of light that can pass through. The authors of
[10] discovered that addition of one gram of dust per square meter reduced light transmittance by 4.1%, while
[11] examined total transmission for various weights per unit area and discovered that the entire transmission reduces linearly with dust mass per unit area. In addition, the study found that the transmittance is affected by the size and shape of the dust particles, with smaller particles having a more significant impact on the transmittance. The study also found that smaller spherical and cubic particles have a more substantial effect on the transmittance than larger particles because they are more equally distributed throughout the surface of the mirror and lessen the amount of light that passes through spaces between the particles. The chemical composition of the dust can also affect the transmittance, with different elements and compounds having different optical properties.
Overall, the transmittance of dust on PV can significantly impact PV system performance, and it is essential to consider the numerous factors that impact the dust particles’ transmittance rate when investigating the impact of dust on PV performance.
3. Dust Reflection
Dust reflection refers to light reflected by dust particles accumulated on PV surfaces and other optical surfaces. The amount of light that may travel through or be reflected by these surfaces can be greatly reduced by dust particles, which lowers the effectiveness and performance of the affected systems
[12]. Dust reflection can be affected by numerous factors, such as the dust particles’ size, shape, and composition, and the amount of dust accumulation on the surface
[13]. The density of the dust deposited on the PV module significantly impacts reflection
[14]. When the density of dust-deposited mass is between 0 and 65 g/m
2, reflectance rises roughly linearly with mass density, from 10.8% to 25.6%. Reflectance stays the same once the mass density exceeds 65 g/m
2.
When dust particles accumulate on a surface, they can create a diffused, scattered reflection of light, reducing the amount of light that can pass through the surface. This is known as “diffuse reflection”. This can happen when dust particles are smaller than 2 mm and accumulate on the surface of the PV module, making it difficult for the light to pass through
[13]. Overall, dust reflection can significantly impact the performance of systems that rely on optical surfaces, and it is vital to consider the numerous factors that affect dust reflection when investigating the effect of dust on PV effectiveness and developing dust mitigation strategies.
4. Dust Emissivity
Emissivity is the ability of dust particles to emit thermal radiation, which can impact the temperature of PV cells. Understanding how dust emissivity affects the thermal behavior of the PV systems is still extremely limited within the current state of knowledge.
The impact of dust emissivity on the thermal behavior of PV has yet to acquire much interest; on the other hand, the impact of dust emissivity on the thermal behavior of building roofs has been investigated. For example, Ref.
[15] discussed the impact of dust accumulation on the thermal performance and heat-gain of building roofs in hot, dry climates, where dust accumulation on building roofs can impact the thermal behavior of the building by affecting the roof’s solar absorptivity and thermal emissivity. In addition, the amount of dust on a surface can also impact the emissivity of dust. As the dust layer thickness increases, the dust particles’ emissivity also increases. Ref.
[16] explained how dust accumulation on a horizontal radiant barrier can affect the thermal performance and stated that insignificant amounts of dust can cause significant increases in the emissivity of radiant barriers. The test results showed that dust levels of 0.34 and 0.74 mg/cm
2 resulted in emissivity values of 0.125 and 0.185, respectively. This occurs because the increased presence of dust particles scatters and absorbs more light, changing the surface thermal properties of the underlying surface.
This entry is adapted from the peer-reviewed paper 10.3390/en16083401