Maintaining the cleanliness of solar panels is crucial for their efficiency and longevity. Dust, dirt, and other contaminants can significantly reduce their ability to generate electricity, making regular cleaning essential.

While the primary method for cleaning solar panels is the wet cleaning (cleaning with demineralized water), the dry cleaning is a method of choice in desertic regions or where water access is limited. While each has its pros and cons, an hybrid approach that combines both methods are gaining popularity. This article explores the benefits and drawbacks of wet and dry cleaning, the factors to consider when choosing a method, and how a hybrid approach can be the best solution.

Wet Cleaning

Wet cleaning involves using demineralized water, sometimes mixed with the appropriate cleaning solutions, to clean the surface of solar panels.

Important note: wet cleaning is approved and recommended by all PV manufacturers.

 Advantages of Wet Cleaning:

• Thorough Cleaning: Water combined with cleaning solutions effectively removes all types of contaminants, including bird droppings, sticky residues, and fine dust.
• Enhanced Efficiency: Ensures that panels are thoroughly cleaned, maintaining optimal efficiency.
• Longer cleaning intervals: a more thorough cleaning will allow the extension of the time between cleanings.
• Reduced Abrasion: Water acts as a lubricant, minimizing the abrasion on the modules. This is specially important on PV modules where the antireflective coating (ARC) is less resistant to abrasion.

Disadvantages of Wet Cleaning:

• Logistical Challenges: Managing water logistics on and off-site can be complex and costly.
• High Water Usage: Depending on the contaminant found and the cleaning tool used (e.g. manual brush or robot) this method can consume significant amounts of water, which is a concern in areas facing water scarcity.
• Increased Costs: Costs related to water usage, transportation, manpower and possibly specialized cleaning agents can add up.

Dry Cleaning

Dry cleaning is simply brushing the surface of the PV modules with a brush without adding water.

Important note: before deciding to opt for dry cleaning, check the O&M manual of your manual to check if the manufacturer approves this cleaning method. Three of the Top 10 PV manufacturers do not recommend or allow dry cleaning. For more information check this article.

 Advantages of Dry Cleaning:

• Water Conservation: Ideal for arid regions where water is scarce, as no water is used.
• Cost-Effective: Eliminates the cost of water and water transportation, and speeds up the cleaning since there is no need for hose management or frequent refills of the tractor.
• Simplified Logistics: Easier to manage logistics on and off-site.

 Disadvantages of Dry Cleaning:

• Manufacturer Restrictions: Not allowed by several PV manufacturers due to the risk of abrasion damages.
• Higher Abrasion: Lack of water lubrication can lead to higher abrasion on the modules and faster degradation of surfaces, particularly the anti-reflective coating (ARC).
• Effectiveness: Less effective in removing stubborn soiling, bird droppings, sticky residues or harsh soiling. Particularly ineffective against cemented soiling.
• Frequent Cleaning Needed: May require more frequent cleaning as it is not as thorough as wet cleaning.

Choosing the Right Method

When deciding between wet and dry cleaning, several factors should be considered:

• Location and Climate: In arid regions with limited water availability, dry cleaning may be more practical and beneficial. On the other hand, areas with heavy pollution or significant bird activity might benefit more from wet cleaning's thoroughness.
• Panel Type and Installation: Some panels have coatings that could be sensitive to certain cleaning methods. The angle and accessibility of the panels also play a role in determining the best cleaning approach.

Hybrid Cleaning: The Best of Both Worlds?

Hybrid cleaning combines the strengths of both wet and dry methods to optimize solar panel maintenance. This method consists of adding one or two wet cleanings on sites that are dry cleaned several times per year.

This approach addresses the limitations of using either method alone and maximizes the benefits by combining them.

 Advantages of Hybrid Cleaning:

• Enhanced Effectiveness: By using both methods, hybrid cleaning ensures a thorough removal of all contaminants, from loose dust to hardened residues.
• Water Efficiency: While wet cleaning handles stubborn soiling, regular dry cleaning reduces the overall frequency of water use.
• Cost Efficiency: Balancing dry and wet cleaning helps manage costs related to water logistics and consumption.
• Adaptability: This method can be tailored to different environmental conditions and contamination levels, providing flexibility.

Tackling Cemented Soiling with Hybrid Cleaning

Cemented soiling occurs when contaminants adhere strongly to the panel surface, forming a hardened layer that dry cleaning alone cannot remove. This is usually the result of environmental factors such as the combination of dust and dew, bird droppings and industrial pollutants such as cement or stone dust hardened by the moisture from the dew. Once these have dried on the surface of the panel, dry cleaning them becomes an almost impossible mission.

Role of Wet Cleaning in Hybrid Approach:

• Effectiveness: Wet cleaning is crucial for dissolving and removing hardened soiling and residues. Water, in these cases combined with appropriated cleaning agents, breaks down these contaminants effectively. Make sure that the solutions used are approved by the manufacturers and formulated for solar panels.
• Implementation: After several dry-cleaning sessions, a wet cleaning session can ensure that any remaining stubborn dirt is thoroughly removed, preventing the build-up of cemented soiling and maintaining panel efficiency.

Enhancing Cleaning with Soiling Mitigation (Anti-Soiling) Coatings

Applying a soiling mitigation coating, besides reducing the buildup, will specially help reduce the adhesion of the soiling to the panel. Using a coating that is applied during the wet cleaning, such as the Antistatic Solar Armor from Chemitek Solar, insures that there are no costs of application nor the need for specialized labor.

The antiadherent properties of this protective barrier will enhance the quality of dry cleaning by keeping the soiling looser on the surface and thus easier to remove.

Conclusion

Both dry and wet cleaning methods have their own advantages and challenges. The choice between the two largely depends on specific circumstances, including geographical location, environmental conditions, and cost considerations. For many O&M teams, Asset owners, or Managers a combination of both methods is the most effective approach. A combination of both methods – hybrid cleaning – often proves to be the most effective approach. This strategy allows for regular maintenance with minimal resource use while ensuring that stubborn contaminants are adequately addressed. By understanding the specific needs of their solar installations and environmental conditions, stakeholders can optimize the performance and longevity of their solar energy systems.

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