As the global consensus on green development strengthens, the demand for energy has reached unprecedented levels. To mitigate environmental pollution caused by traditional fossil fuels, the development of new energy technologies and low-carbon economies has become a widespread priority worldwide. Solar energy, as an abundant, widely distributed, and inexhaustible green resource, is recognized as a crucial solution to the global energy crisis and reducing greenhouse effects. In recent years, global solar power installation capacity has been rising steadily, with solar energy rapidly capturing a larger share of the renewable energy market. According to statistics from the International Renewable Energy Agency (IRENA), the global solar capacity added 346 GW in 2023, a 74% increase year-on-year, bringing the total installed capacity to nearly 1419 GW by the end of 2023. This growth is particularly prominent in regions with high solar radiation intensity, such as Asia, North America, Europe, and South America. Asia leads in total installed capacity, with China, Japan, and India accounting for over 90% of the region’s capacity. Europe follows, with Germany, Spain, and Italy as key contributors, while North America is dominated by the United States. South America, Oceania, and the Middle East, though with smaller capacities, are experiencing rapid growth, driven by countries like Brazil, Australia, and the United Arab Emirates.
Solar panels are often exposed to harsh outdoor environments, where they accumulate dust, bird droppings, and other contaminants, leading to a significant drop in transmittance and adversely affecting power generation efficiency and panel lifespan. Regular cleaning of solar panels is a mainstream practice to enhance photoelectric conversion efficiency. With the rapid expansion of the photovoltaic industry and varying geographical conditions, new cleaning technologies are being developed. In this article, I will review the current state of solar panel cleaning technologies, discuss mainstream methods and their principles, and analyze their development trajectories, advantages, disadvantages, and applicability. The future of solar panel cleaning technology should emphasize unmanned operation, high efficiency, excellent cleaning quality, safety, and strong adaptability. Key trends include mechanization, intelligence, customization, and integration.
Contaminant coverage on solar panels has been extensively studied globally. The most common cleaning method is manual cleaning, but as photovoltaic power plants scale up and panel sizes increase, issues like poor cleaning effectiveness and rising costs become apparent. Thus, specialized cleaning devices are becoming the mainstream solution. Popular approaches include large-scale cleaning machinery or robots, followed by methods integrated directly with solar panels, such as electrostatic dust removal and self-cleaning films. Researchers have also investigated various water-soluble reagents for cleaning, including water, detergents, liquid soap, sodium-based cleaners, and deep eutectic solvents, to address different types of contaminants. These studies highlight the importance of optimizing cleaning agents for specific environmental conditions.
To address maintenance challenges in the rapidly growing photovoltaic industry, new cleaning technologies are emerging. I will summarize the research status of solar panel cleaning technologies, explain the principles behind current methods, and provide a comparative analysis. The cleaning of solar panels typically involves the removal of contaminants through water, wind, brushes, vibration, or other means. Main cleaning methods can be categorized into natural cleaning, manual cleaning, semi-automatic cleaning, and automatic cleaning.
Natural Cleaning
Natural cleaning relies on environmental factors like rainfall and wind to clean solar panels. However, the effectiveness depends on variables such as wind speed, direction, rainfall intensity, and the tilt angle of the solar panels. For instance, studies in desert photovoltaic parks have shown that wind can improve power generation efficiency by blowing off dust and reducing panel surface temperature. However, research indicates that wind is less effective at removing particles smaller than 50 µm, and for particles below 10 µm, wind speeds below 25 m/s are insufficient due to strong adhesion forces between particles and the air. The relationship between wind speed and particle removal can be described by the following equation for critical wind velocity: $$ v_c = \sqrt{\frac{2mg}{\rho A C_d}} $$ where ( v_c ) is the critical wind velocity, ( m ) is particle mass, ( g ) is gravity, ( \rho ) is air density, ( A ) is cross-sectional area, and ( C_d ) is drag coefficient. This illustrates the challenges in relying solely on natural elements for cleaning solar panels.
Manual Cleaning
Manual cleaning is one of the earliest methods and is still widely used in many photovoltaic plants worldwide. It involves workers using high-pressure water guns or cleaning brushes to remove contaminants from solar panels. This approach offers advantages such as low equipment costs, simplicity, and minimal environmental pollution. However, it has significant drawbacks: it requires a large workforce, leading to high labor costs; it consumes substantial water resources, making it unsuitable for water-scarce regions; and it poses safety risks in hazardous environments where solar panels are installed. The efficiency of manual cleaning can be expressed in terms of cleaning rate: $$ E_{\text{manual}} = \frac{A_{\text{cleaned}}}{t \cdot N} $$ where ( E_{\text{manual}} ) is cleaning efficiency, ( A_{\text{cleaned}} ) is area cleaned, ( t ) is time, and ( N ) is number of workers. This highlights the inefficiency for large-scale solar farms.
Semi-Automatic Cleaning
Semi-automatic cleaning builds on manual methods by incorporating advanced equipment, such as vehicle-mounted solar panel cleaning machines. These systems typically consist of a mobile chassis with hydraulic arms equipped with rotating brushes. Operators control the arms via joysticks to clean the panels. This method reduces labor requirements and provides good cleaning quality but is limited by terrain constraints and high energy consumption. The cleaning effectiveness can be modeled as: $$ C_{\text{semi}} = k \cdot B \cdot V $$ where ( C_{\text{semi}} ) is cleaning capacity, ( k ) is a constant, ( B ) is brush rotation speed, and ( V ) is vehicle speed. Despite improvements, semi-automatic systems are not ideal for all environments, particularly those with complex layouts.
Automatic Cleaning
Automatic cleaning technologies aim to reduce human intervention and increase efficiency. They can be divided into robotic automatic cleaning, electric curtain self-cleaning, and nano-film self-cleaning.
Robotic Automatic Cleaning
Cleaning robots come in two types: rail-guided and autonomous mobile robots. Rail-guided robots require pre-installed rails on solar panel frames, where drive wheels move along the rails while brushes clean the surface. Although effective, the installation process is labor-intensive and costly. An improved version eliminates the need for external rails by adjusting the robot’s wheelbase to fit directly onto panel frames, enabling cleaning of single rows in photovoltaic arrays. These robots typically operate without water, making them suitable for arid regions. Autonomous mobile robots do not require additional rails or connections; they are placed directly on solar panels and clean automatically. To prevent slipping on tilted surfaces, they use treads or suction cups. For example, some robots can adhere to panels with inclines up to 70° and achieve cleaning efficiencies of 35 m² per hour. The motion dynamics can be described by: $$ F_{\text{adhesion}} = \mu \cdot N $$ where ( F_{\text{adhesion}} ) is adhesive force, ( \mu ) is friction coefficient, and ( N ) is normal force. This ensures stability during operation.
Electric Curtain Self-Cleaning
Electric curtain self-cleaning, also known as electrostatic dust removal, was initially proposed for space applications. The principle involves charging an electrodynamic screen (EDS) membrane, which causes charge transfer between charged atoms and dust particles. Positively charged atoms and negatively charged dust particles interact with an alternating electric field generated by electrodes on the solar panel, lifting particles into the air and away from the surface. Recent advancements use alternating current to create electric fields, improving efficiency and reducing costs. For instance, a system with embedded wire electrodes and a high-voltage power supply generates alternating electrostatic fields that produce standing waves, causing dust particles to flip and roll off due to gravity. The electric field strength ( E ) required for particle removal is given by: $$ E = \frac{F_e}{q} $$ where ( F_e ) is electrostatic force and ( q ) is particle charge. However, this method is less effective on wet contaminants and is best suited for dry, desert environments.
Nano-Film Self-Cleaning
Nano-film self-cleaning involves applying a coating to solar panels that enables self-cleaning without additional energy input. Two types are prevalent: super-hydrophilic and super-hydrophobic films. The self-cleaning capability depends on the contact angle ( \theta ) formed at the interface between liquid droplets, the film surface, and dust particles. Super-hydrophilic films exhibit photocatalysis, decomposing contaminants under sunlight, inspired by photosynthesis. Super-hydrophobic films mimic the “lotus effect,” where microstructures on surfaces like lotus leaves cause water droplets to bead up and roll off, carrying dirt away. The contact angle is defined by Young’s equation: $$ \cos \theta = \frac{\gamma_{SV} – \gamma_{SL}}{\gamma_{LV}} $$ where ( \gamma_{SV} ), ( \gamma_{SL} ), and ( \gamma_{LV} ) are solid-vapor, solid-liquid, and liquid-vapor surface tensions, respectively. For super-hydrophobicity, ( \theta > 150^\circ ), and for super-hydrophilicity, ( \theta < 10^\circ ). While these films offer high cleaning efficiency, challenges include durability in harsh environments and the need to balance optimal panel tilt for light absorption with self-cleaning effectiveness.
Comparison of Cleaning Technologies
To provide a clear overview, I have compiled a comparative table of existing solar panel cleaning technologies based on cost, advantages, disadvantages, and cleaning efficiency. This analysis highlights the evolution toward unmanned and efficient solutions.
| Cleaning Technology | Cost | Advantages | Disadvantages | Cleaning Efficiency |
|---|---|---|---|---|
| Natural Cleaning | None | No cost involved | Highly unpredictable | Variable |
| Manual Cleaning | Low | Low cost, simple operation, good quality | High labor and water consumption | Low |
| Semi-Automatic Cleaning | Medium | Reduced labor, good quality | Terrain-dependent, energy-intensive | Medium |
| Robotic Cleaning (Rail-guided) | High | Minimal labor, no water needed | Requires rail installation | High |
| Robotic Cleaning (Autonomous) | High | Minimal labor, low water use | High R&D costs, need for docking | High |
| Electric Curtain Self-Cleaning | High | No labor or water, fast and effective | High installation cost, requires electricity | High |
| Nano-Film Self-Cleaning | High | No labor, water, or energy needed | High material cost, weak self-cleaning, low light transmittance | High |
From this table, it is evident that cleaning technologies are advancing toward unmanned and efficient operations. Electric curtain and nano-film methods offer the highest efficiency but face cost and applicability challenges. Robotic cleaning strikes a balance between cost and efficiency, with potential for widespread adoption if technology matures. Current methods lack specificity for different contaminants, with semi-automatic and electric curtain cleaning suited for arid areas, and nano-films for humid regions. Manual and semi-automatic methods, while common, require improvements in cost and resource usage.
Future Trends and Development Directions
As the global photovoltaic industry expands, effective dust removal from solar panels is crucial to maintain power generation efficiency and overall plant performance. Based on current research and maintenance needs, future solar panel cleaning technologies should embody four key characteristics: unmanned efficient operation, high cleaning quality, safety, and strong adaptability. I will now describe an intelligent cleaning system that aligns with these trends, incorporating drones, robots, and cloud management for optimized performance.
In this proposed solar panel intelligent cleaning system, drones equipped with cameras capture images of solar panel surfaces to detect contaminants using advanced algorithms. The system classifies pollutants and dispatches cleaning robots to targeted areas. Cleaning robots, equipped with brushes and water tanks, perform tailored cleaning based on contaminant type and send completion signals to a cloud management platform. The platform generates electronic maps of the photovoltaic plant, tracks the positions of drones and robots in real-time, and coordinates their movements. For instance, after cleaning, the platform directs the nearest drone to retrieve and redeploy the robot to the next panel. To address energy and water needs, an intelligent charging and water pumping system is integrated, allowing drones to autonomously recharge and robots to refill water supplies as needed. This system achieves pollutant detection, targeted cleaning, and fully automated operations, representing the future of solar panel maintenance.
Looking ahead, the main development trends for solar panel cleaning technology include mechanization, intelligence, customization, and integration. Mechanization will replace manual methods with robotic systems to meet the demands of large-scale plants. Intelligence will involve three aspects: smart decision-making before cleaning, such as analyzing contamination levels and scheduling cleaning cycles; real-time control during cleaning, using environmental sensing and positioning to optimize parameters; and post-cleaning evaluation through surface assessment and performance monitoring. Customization will address the diverse structures and environments of photovoltaic plants, requiring tailored solutions developed through collaborations between research institutions and enterprises. Integration will encompass multidisciplinary research combining materials, energy, and information technologies; incorporating cleaning requirements into plant design; and embedding cleaning protocols into maintenance standards for holistic plant management.
In conclusion, the advancement of solar panel cleaning technologies is essential for sustaining the growth of the photovoltaic industry. By embracing mechanization, intelligence, customization, and integration, we can overcome current limitations and ensure efficient, safe, and adaptable cleaning solutions. Continued innovation in this field will play a vital role in maximizing the potential of solar energy as a cornerstone of global renewable energy strategies.