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As energy demands continue to rise around the world, there is an ever-greater need for an alternative power source to take the place of finite fossil fuels. A new generation of renewable energy technologies has emerged to address this need. Solar power is one of the most popular choices, offering a clean and sustainable solution that can be put in place almost anywhere.

Solar power systems are found everywhere in the world, and solar modules represent a significant part of the landscape. However, soiling is an important issue for these surfaces as well. Soiling causes a drop in energy yield, especially under high insolation and water shortage conditions. In out-and-out soiling locations, sufficient steps to control it could overly offset the remarkable progress made over the past few decades in solar cell efficiency in some circumstances.

What is Soiling?

Solar panels are an integral part of solar systems that must be mounted correctly and free of environmental problems. However, one environmental problem should not be ignored – the accumulation of atmospheric dust on their surfaces. The efficiency of solar panels decreases significantly as this dust accumulates on their surfaces. This accumulation is referred to as soiling.

Soiling in Solar Panels – Reasons

Soiling blocks or scatters incident light, leading to a reduction in power output. It is generally composed only of common substances like mineral dust, bird droppings – fungi, lichen, and pollen. Light soiling is the most widespread form and it affects many different kinds of solar power systems, including conventional photovoltaics, concentrated photovoltaics, and concentrated solar (thermal) power. The accumulation of soil and dust–known as soiling–formed a film (and this is now visible) that covers the solar modules’ surface.

3 Factors Affecting Solar Panel Soiling

Soiling, the accumulation of dirt on solar panels, reduces their efficiency. So, it is therefore necessary to clean them thoroughly in order to achieve flawless, or peak performance, as dirt accumulation reduces the light intensity of solar radiation falling on their surfaces and this results in power being taken out of them.

Here are 3 factors that affect the solar panel performance,

Climatic Conditions

Local climatic conditions, in conjunction with the geographical location of the solar power plant, significantly affect soiling. Extremely dry or humid conditions, coupled with continuous wind, lead to the deposition of soil and dust particles on solar modules. Over time, these particles may accumulate along the module frame, a phenomenon known as cementing. Cemented dust particles are mostly irremovable and cause a fixed reduction in power output, further damaging the module permanently.

Tilt Angle of Modules

The tilt angle of the module is essential to the production of a PV power plant. The optimum tilt angle is usually the location latitude, however, practical constraints often result in lower tilt angles. Lower tilt angles, sometimes as low as 5º, lead to increased deposition of dust. During the design phase, soiling losses are generally 3-5%. However, decreases in tilt angle can give rise to power losses that are as much as 10-12%.

Type of Liquid Used for Cleaning

The type of liquid used in cleaning is going to have either a directly beneficial or harmful effect on the solar module glass surface. When the cleaning liquid evaporates, its residue on the solar glass remains. Evidently, transmittance through the glass decreases as a result. The chemical composition of the cleaning liquid may react with the glass surface, causing dust to stick and settle on the glass.

Potential Solutions to Soiling Losses in Solar Systems

One of the significant solutions that can likely solve solar panel soiling is a larger inclination angle that can lead to less soiling accumulation and a higher likelihood of rain having a cleaning effect.

Here are five potential solutions to soiling losses in solar systems.

Site Selection and System Design

During site selection and system design careful planning can help mitigate soiling effects. Large differences in soiling deposition rates can exist within a region, mainly influenced by proximity to roads, agriculture, industry, and the direction of the prominent wind. The inclination angle of the solar panels also plays a crucial role, with larger inclination angles leading to less soiling accumulation and a higher likelihood of rain having a cleaning effect. Solar panels can be designed to minimise the impact of soiling by using smaller solar cells, panels without frames, or alternative electrical configurations.

Solar Panel Design

Solar panels can be designed not to be laden down with soiling. Options include using smaller solar cells (e.g., half-cells), panelless solar panels to avoid dirt collecting at the edges, or employing alternative electrical configurations (e.g., more bypass diodes). Wet-chemically etched nanowires and hydrophobic coatings have been shown to remove 98% of dust particles.

Cleaning

Regular cleaning is the most popular way to prevent soiling losses. Manual cleaning is done by people using brushes or mops. Semi-automatic cleaning requires machines, usually a tractor equipped with revolving brushes. Fully automatic cleaning means robots come out at night to clean the solar panels. Water is usually used for cleaning, but dry-cleaning methods are also used. Dry cleaning is preferable in places where water is scarce or expensive.

Anti-soiling Coatings

Anti-soiling coatings can be applied to the surface of solar panels or mirrors to reduce the adhesion of dust and dirt to them. Some coatings are designed to add self-cleaning properties, increasing the probability that the surface will be cleaned by rain. However, as of 2019, no particular anti-soiling technology had been universally adopted because of a lack of durability.

Electrodynamic Screens

In fact, electrodynamic screens are uniform networks of conducting wires woven into the structure of solar panels or mirrors. To move them off the surface, the grid is traversed by alternating voltages that set up intense electromagnetic fields which interact with the cultivated particles. Though this technology has been demonstrated in the laboratory, it still needs to be shown in practice.

Soiling Losses – Impact on the Performance of Photovoltaic Power Plants

On a global scale, soiling of solar photovoltaic (PV) systems from dust and snow–and the resulting loss in energy yield–is the second most influential factor affecting system yield after irradiation level. With large utility PV plants, soiling may have adverse effects in arid regions, so some means to alleviate such problems must be designed and implemented in mass. This international switch to collective cleaning results in reduced earnings because both expenditures on maintenance are higher (which were only unnecessary costs up till now); and capital investment must be made for anti-soiling coatings, as well as cleaning robots and their upkeep.

Solar Soiling Loss Calculations

The soiling ratio (SR), as defined in the technical standard IEC 61724-1, is one measure of the level of soiling in a photovoltaic system. A distinct standard of the soiling ratio generalises the power ratio that is used in solar cell calculations and adds an important soiling parameter.

SR = Actual power output/ Expected power output if clean

When,

• SR=1, there is no soiling energy which is similar to that of the clean surface as output
• SR=0, there is so much soiling that no electricity is output.

The soiling deposition rate (or soiling rate) may colloquially be seen as the speed with which soiling loss changes over time, measured in percentage by day. Note that many sources define the soiling rate as being positive when periods are characterised by increasing soiling losses; however, some authorities use the opposite sign.

Finally, in order to fully tap the potential of solar power to meet world energy demands and employ it as a tool for achieving carbon neutrality or even negative emissions it is necessary to miniaturise PV systems. Soiling affects the efficiency of the solar system by cutting down on the irradiation getting to panels and by raising cell temperature leading to low power output. Regular cleaning, and monitoring through soiling stations, considering environmental factors are just as important for solar-powered systems to be ready for managing their own maintenance feasibly from the ground up.