Abstract
This study explores the impact of surface contamination—namely mud, vegetation, and bio-organic matter like slugs—on the energy performance of photovoltaic (PV) panels. Using consistent environmental conditions and controlled measurement protocols, we compare the output of solar modules before and after cleaning. The results reveal a notable increase in performance once panels are cleaned, reinforcing the importance of maintenance in real-world deployments.

1. Introduction
The effectiveness of photovoltaic panels is highly sensitive to the cleanliness of their surface. Contaminants can significantly reduce the amount of sunlight reaching the solar cells, thereby decreasing power output. This issue is especially pronounced in agricultural or wooded areas, where natural soiling agents are abundant.In this field investigation, modules were affected by multiple soiling types including mud splatter, plant matter, and slugs. We evaluated their performance before and after cleaning to quantify the loss caused by surface contamination.

2. Methodology
A total of 40 identical PV modules were tested as part of a field campaign using Solar Tester’s mobile testing lab. Each module was measured twice—once in its contaminated state, and once immediately after cleaning—under consistent environmental conditions to isolate the effect of soiling.

For this article, we selected a sample of 9 modules that reflect the overall trend observed in the broader dataset. These samples were chosen for clarity and to illustrate the range of impacts that surface contamination can have on panel performance.

3. Results
The following table presents the watt-peak (Wp) output of each of the 9 sampled modules before and after cleaning:

Sample Results – Solar Panel Performance Before & After Cleaning

Module 1 Dirty: 377.3 Wp Clean: 407.1 Wp Gain: +29.8 Wp
Module 2 Dirty: 354.2 Wp Clean: 408.3 Wp Gain: +54.1 Wp
Module 3 Dirty: 388.0 Wp Clean: 407.3 Wp Gain: +19.3 Wp
Module 4 Dirty: 362.0 Wp Clean: 407.1 Wp Gain: +45.1 Wp
Module 5 Dirty: 338.5 Wp Clean: 404.8 Wp Gain: +66.3 Wp
Module 6 Dirty: 382.0 Wp Clean: 408.7 Wp Gain: +26.7 Wp
Module 7 Dirty: 387.6 Wp Clean: 404.4 Wp Gain: +16.8 Wp
Module 8 Dirty: 351.3 Wp Clean: 404.5 Wp Gain: +53.2 Wp
Module 9 Dirty: 387.1 Wp Clean: 383.2 Wp Gain: -3.9 Wp

Average Dirty Output: 370.9 
Wp Average Clean Output: 403.4 Wp 
Average Gain: +32.5 Wp (~8.8%)

Cleaning improved average performance by +32.5 Wp, or +8.8%.

4. Discussion
The results highlight the significant impact of surface soiling on solar panel output. Across the sampled modules, the average gain in power after cleaning was 32.5 Wp, representing an 8.8% increase in performance.Notably, the lowest-performing panel in the dirty state (Module 5 at 338.5 Wp) showed a gain of 66.3 Wp upon cleaning—a 19.6% increase, emphasizing how variable and locally severe soiling can be.This demonstrates that in certain environmental conditions, even short-term surface contamination can cause meaningful losses in energy production.

5. Conclusion
Our controlled field test underscores the measurable performance loss caused by bio-organic and environmental soiling. Even in a small sample, the cleaning process resulted in consistent and significant power increases. This reinforces the necessity of regular inspection and cleaning, especially in installations located near vegetation, farmland, or damp conditions where slug activity is prevalent.

6. Recommendations
Routine Maintenance: Establish regular cleaning protocols for PV systems installed in high-risk soiling environments.
Preventive Design: Consider the use of anti-soiling coatings and mechanical barriers to limit exposure to mud and organic matter.
Comprehensive Diagnostics: Deploy mobile labs for detailed module-level performance testing before installation, and validate system health after installation using methods such as mobile testing.

These strategies provide critical insight into module condition and enable early detection of underperformance or defects that might be amplified by environmental soiling.

For more information about this research feel free to contact us through info@solartester.nl

Authors:  Selmir Avdic
Date: 18-04-2025
Location: Goirle, The Netherlands

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