How do you measure soiling?

Soiling Measurement in Photovoltaic Power Plants: Principles, Methods, and Importance 

What is Photovoltaics?  

Photovoltaics (PV) is a technology that directly converts solar energy into electricity through the photovoltaic effect. A typical photovoltaic system consists of solar panels, inverters, mounting structures, and monitoring systems. The silicon-based or other semiconductor materials in solar panels absorb sunlight, generating direct current (DC), which is converted into alternating current (AC) through the inverter for use in homes, industries, or power grids. 

Photovoltaic technology is a core part of renewable energy, widely used in residential rooftops, commercial buildings, and large-scale ground-mounted power stations. Its advantages include zero emissions, sustainability, and low operational costs, but its power generation efficiency can be significantly affected by environmental factors such as soiling.

Why Test Soiling in Photovoltaic Power Plants?  

Soiling refers to the deposition of pollutants like dust, sand, pollen, and bird droppings on the surface of solar panels, affecting their ability to absorb sunlight. The reasons for testing soiling include: 

1. Power Generation Loss: Soiling can cause a power loss of 5% to 30%, and in arid or highly polluted areas, this loss can be even higher.

2. Optimizing Cleaning Frequency: By monitoring the degree of dirt accumulation, a scientifically based cleaning schedule can be established to avoid unnecessary cleaning costs.

3. Reducing O&M Costs: It helps reduce water, electricity, and labor costs, while preventing long-term damage to the equipment from accumulated dirt.

4. Data-Driven Decision Making: Provides real-time data to support power plant managers in formulating scientific maintenance strategies.

5. Regional Environmental Analysis: Soiling characteristics vary by region, and testing helps create adaptive maintenance plans. 

In the highly competitive photovoltaic market, accurate pollution monitoring is key to ensuring the profitability of a power plant.

How to Measure Soiling? Common Tools and Methods 

1. Soiling Measurement Principles  

Soiling Ratio (SR) represents the cleanliness percentage of the solar panel surface (50% to 100%), reflecting the relationship between transmittance and power generation efficiency. For example, an SR of 80% means a 20% potential loss in power generation. 

2. Common Tools for Measuring Soiling   

2.1. Soiling Monitoring Sensors (Soiling Sensor)  

   - Principle: Uses optical infrared photodiodes to emit light and detect the reflected intensity, analyzing surface cleanliness.  

   - Features:  

     - Power Supply: DC 12V, approximately 1W power consumption  

     - Output: RS485 signal, supports MODBUS protocol, easy integration into management systems  

     - Accuracy: ±1% (90%-100%), ±3% (80%-90%), ±5% (50%-80%)  

     - Optional Function: Temperature measurement (-50℃ to +100℃, accuracy ±0.5℃)  

   - Advantages: Maintenance-free, easy installation, suitable for new or existing photovoltaic arrays   

2.2. Portable Soiling Meters  

   - Use: For temporary or sample tests, suitable for small power stations or on-site inspections  

   - Method: Measures surface transmittance optically or electrically, requires manual data recording   

2.3. Drones & Imaging Systems  

   - Application: Equipped with high-resolution cameras or infrared sensors to scan large photovoltaic arrays and identify polluted areas  

   - Applicable Scenarios: Large-scale power stations, but expensive and requires professional operation   

3. Main Soiling Testing Methods 

3.1. Reference Module Method  

   - Principle: Uses two identical photovoltaic modules, one kept clean (reference module) and the other naturally accumulating dust (test module)  

   - Measurement: Compare output power or current to calculate the Soiling Ratio  

   - Advantages: Reflects pollution impact under natural conditions, low cost, intuitive results

3.2. Optical/Imaging Method  

   - Principle: Uses laser scattering devices, cameras, or image processing technologies to analyze surface pollution levels  

   - Applicable Scenarios: Laboratory environments or high-precision monitoring

3.3. Transmittance Sensor Method  

   - Principle: Installed above the module to monitor the attenuation of sunlight through the pollution layer in real time  

   - Advantages: Can monitor online for extended periods, suitable for automated operations   

3.4. Soiling Station / Soiling Measurement Sensor  

   - Components: Integrated reference module, irradiance meter, thermometer, current/voltage collection module, etc.  

   - Connection: Connected to SCADA system for automated data collection and alerts  

4. Data Analysis and Application 

Based on the Soiling Ratio (SR), maintenance thresholds can be set:  

- SR ≥ 95%: No cleaning needed  

- SR 85%～95%: Cleaning can be considered based on cost-benefit analysis  

- SR < 85%: Immediate cleaning is recommended  

By analyzing the data, managers can optimize the cleaning plan, balancing power generation revenue with maintenance costs.

Conclusion 

Photovoltaic technology is a pillar of clean energy, but pollution on the surface of solar panels can significantly reduce power generation efficiency. Through pollution monitoring, photovoltaic power plants can achieve higher operational efficiency and economic benefits. 

Currently, the main pollution measurement methods include:  

- Reference Module Method (low cost, intuitive results)  

- Optical Sensor Method (high precision, automated)  

- Drone Remote Sensing (suitable for large-scale power stations) 

With technological advancements, more intelligent soiling monitoring solutions are being promoted. For photovoltaic power plant managers, investing in pollution monitoring systems is not only a technological upgrade but also a crucial step towards intelligent operations. Whether it's small rooftop systems or large ground-based power stations, accurate pollution measurement can help maximize power generation, reduce operating costs, and ensure long-term profitability. 

Explore the pollution monitoring solutions that suit you and help your photovoltaic power plant run efficiently!

NBL-W-PSS Soiling Sensor Data Sheet

NBL-W-PSS Soiling Sensor Photovoltaic Dust Monitoring Instrument Data Sheet.pdf