Photovoltaic power generation is the most common new energy method nowadays, which has brought great convenience to the development of society. However, dust can have a significant impact on the energy conversion of photovoltaic panels. Starting from the types of dust that affect photovoltaic power generation, this article introduces the principle of dust affecting power generation, dust cleaning methods, etc. in order to provide reference for relevant researchers.
The energy issue is a key issue related to the development of the world. The traditional power generation method is mainly based on thermal power generation, but it will bring corresponding pollution and energy waste. However, water conservancy and wind power generation also have their limitations, requiring certain geographical conditions to ensure the need for electricity in production and life. As an efficient and clean renewable energy, solar energy can be fully utilized throughout the world. According to the latest data, as of June 18, 2021, the installed capacity of solar power generation in China was 260 million kilowatts, a year-on-year increase of 24.7%; In the power supply projects of major power generation enterprises in China, solar power generation is 11.7 billion yuan, an increase of 8.9% year-on-year. Therefore, the position of solar power generation in China’s energy industry is increasing day by day. Dust is one of the key factors affecting the efficiency of solar power generation, which not only hinders the absorption of solar energy by photovoltaic panels, but also damages solar power generation facilities in serious cases. If the impact of dust on power stations is estimated to be more than 5% based on the global installed capacity of 500GW, the annual loss caused by dust affecting photovoltaic power generation systems will be as high as $5 billion, and the loss will become increasingly serious as the installed capacity of power stations increases. Regular cleaning of photovoltaic power generation components is a necessary measure to effectively reduce the impact of dust.
1. Source and characteristics of dust
1.1 Source of dust
Dust is a small particle that is unevenly dispersed in the air, mainly composed of powdered substances such as soil foam, industrial dust, combustion smoke, insect eggs, and so on, which poses significant harm to human health. Generally, when the dust is less than 10 μ M can have an impact on human health; When dust is less than 2.5 μ M (PM2.5) can pass through the human alveoli directly to the blood, causing damage to human tissues and organs. According to the source, dust can be divided into natural dust and man-made dust. Natural dust is caused by the formation of small particles of soil, rock, etc. through natural long-term weathering and corrosion, and then transmitted to various regions of the world through natural atmospheric movement; Anthropogenic dust refers to small particles generated by human daily production activities, such as cement, limestone, and other dust in the construction industry, dust caused by exhaust emissions from transportation vehicles, and dust caused by exhaust emissions from industrial production.
1.2 Properties of dust
The properties of dust are mainly divided into physical and chemical properties, both of which can have an impact on solar panels. Its physical properties include thermal conductivity, water absorption, and friction. Thermal conductivity refers to the ability of dust to conduct solar energy heat. According to different properties of dust, it can be divided into strong thermal conductivity dust and weak thermal conductivity dust; Water absorption refers to the ability of dust to absorb moisture in the air. Dust with poor water absorption is easier to remove, while dust with good water absorption is more difficult to remove; Frictionality refers to the friction that the appearance of dust affects the dust movement process, thereby affecting its removal effect. The chemical properties of dust are mainly reflected in its acidity and alkalinity. Due to the adsorption effect of dust, it can adsorb substances in the air to itself, thereby reflecting its acidity and alkalinity. Due to its different acidity and alkalinity, the corrosion effect on photovoltaic panels is also different, so the cleaning methods for different dust are also different.
2. Impact principle of dust on photovoltaic power generation
2.1 Occlusion effect
The shielding effect refers to the fact that dust covers the photovoltaic panel and blocks its absorption and conversion of solar energy, mainly affected by the particle size of dust. Firstly, the larger the particle size, the stronger the resistance to sunlight, and the less basic energy that solar energy radiates onto photovoltaic panels; Secondly, dust not only has a blocking effect on light, but also, due to the reflection and scattering effects of dust between the gaps of dust particles, it once again disperses the incident light source, thereby affecting the conversion of photoelectric effects. According to relevant research, the output power of clean solar panels is 15% higher than that of ash deposited solar panels, and the higher the amount of ash deposited, the stronger the impact on the output power.
2.2 Temperature effect
The impact of dust on solar panels is also reflected in its impact on the thermal balance. For a clean solar panel, its entire light receiving surface is uniform, so it can achieve balance. If dust, leaves, or even bird droppings are stored on the surface of the solar panel, the heat dissipation of the solar panel at the sheltered area will be hindered and its thermal balance will be damaged. Over time, the temperature at the sheltered area will be higher than that at the unshielded area, and some parts will have dark and burnt spots due to excessive temperature – hot spots. This not only leads to the melting of solar cells’ solder joints, aging of packaging materials, and affecting the battery’s service life, but also brings potential safety hazards in serious cases.
2.3 Corrosion Effects
The outer surface of solar panels is usually made of silicon based materials, and most of the welding points are made of metal materials, which are prone to corrosion by acid and alkali substances. When dust is deposited on the solar cell panel, it can adsorb other impurities in the air and become acidic and alkaline, causing damage to the surface of the solar cell and affecting its service life. In addition, after the surface of the solar cell is corroded, there will be pits and pits, making it easier for dust to accumulate, which creates a vicious cycle and further affects the conversion between photoelectricity. When external light impinges on uneven areas of the solar panel, diffuse reflection occurs, leading to the destruction of the uniformity of light transmission in the medium. The rougher the solar panel, the smaller the energy refracted by the light, and the smaller the electrical energy generated by the final conversion, resulting in a reduction in the amount of power generated by the solar cell.
3. Cleaning principle of dust on solar cells
The main reason why dust can accumulate on solar panels is due to the existence of gravity, friction, and van der Waals forces. There are not only interactions between dust and solar panels, but also interactions between dust and dust. Therefore, when removing dust, it is necessary to choose the direction with the smallest force as much as possible. We can synthesize and decompose the forces exerted on the dust on the solar panel to obtain normal and tangential adhesion forces, which can generally be ignored if they are small. When using water to clean solar cells, dust can be easily separated from the solar panel due to its buoyancy effect, which can offset its gravity and van der Waals force. At this time, it is necessary to avoid tangential movement between dust and the solar panel to increase its friction. If you want to speed up the cleaning process, you can also add surfactants to the water to create a strong electrostatic attraction that separates dust from solar panels.
4. Specific measures for cleaning solar panels
4.1 Manual cleaning
Manual cleaning is the most primitive cleaning measure, but due to its long manual operation cycle, low efficiency, and high consumption of human and material resources, it is not suitable for large photovoltaic power plants. Specific manual cleaning methods can be divided into manual dry cleaning and manual water cleaning.
Manual dry cleaning refers to a method in which operators use a mop with a long handle and a special cleaning agent to handle dust. Due to the surfactant contained in the cleaning agent, it can increase the electrostatic attraction between the mop and dust, effectively adsorbing dust, and avoiding the phenomenon of dust flying during cleaning. However, when cleaning, the operator may cause damage to the surface of the solar cell due to improper force.
Manual water cleaning refers to the use of water pipes or sprinklers on a waterwheel by operators to spray water onto the surface of solar cells to clean dust. Compared to manual dry cleaning, it has improved efficiency, but can waste a large amount of water resources; In addition, when water jet is applied, a stress will be applied to the surface of the solar cell, causing the phenomenon of hidden cracks inside it. If ignored, it may cause a short circuit in local areas, affecting photoelectric conversion; When using water for cleaning, improper handling can cause water stains on the solar panel, affecting light penetration. If cleaning in winter, ice can also occur, which can also affect light penetration. Therefore, it is not recommended to use.
4.2 Semiautomatic cleaning
The semi-automatic cleaning is mainly operated by specialized engineering vehicles. Compared to manual cleaning, it relies less on water and has a uniform force, which does not lead to cracking of the solar cell; However, semi-automatic cleaning has strict requirements for the height, width, and array spacing of photovoltaic modules, so its use is limited.
4.3 Fully automatic cleaning
Fully automatic cleaning is the process of installing cleaning components onto the array of photovoltaic modules and completing the cleaning of solar cells through program control. Intelligent cleaning robots have emerged in China, which can complete the cleaning of solar cells under relatively difficult conditions. They have the advantages of intelligence, automation, water free, and uniformity, but they have the disadvantages of being expensive and not suitable for handling when faults occur.
5. Summary
With the development of technology, new dust removal methods such as ultrasonic cleaning, pneumatic cleaning, electrostatic cleaning, and laser cleaning have also been applied to photovoltaic power plants. Therefore, the power station management personnel should choose a suitable cleaning method for their own power station to maximize the economic benefits of the power station.
